The Anatomy
                                _of the_
                             Domestic Fowl


                                  _By_
                      B. F. Kaupp, M. S., D. V. M.

 Poultry Investigator and Pathologist in the North Carolina Experiment
   Station, State Department of Agriculture, and the State College of
   Agriculture; Formerly Director of Anatomy Laboratory, Kansas City
                           Veterinary College


                              Illustrated


                       _Philadelphia and London_
                         W. B. Saunders Company
                                  1918




               Copyright, 1918, by W. B. Saunders Company


                           PRINTED IN AMERICA




                                   To
                    DAN T. GRAY, B. S., A. B., M. S.
            CHIEF, ANIMAL INDUSTRY DIVISION, NORTH CAROLINA
                           EXPERIMENT STATION
                AS A TOKEN OF RESPECT AND GRATITUDE THIS
                          VOLUME IS DEDICATED
                                   BY
                               THE AUTHOR




                                FOREWORD


Advanced work in the study of poultry husbandry is now being done in
this country, to a greater or less extent, at all the two score and more
Agricultural and other Colleges and Experiment Stations. From these
institutions comes the demand for a text-book on the Anatomy of the
Domestic Fowl. No complete text-book on the subject, up to the present,
has existed. It is with the hope of meeting the demand that this book is
published.

In supplementing the information gathered from the books and articles
listed in the bibliography, the author has spent much time and effort in
obtaining the matter here presented. As this, however, is the initial
complete text on the subject necessarily much remains to be added and
corrected. The author would welcome suggestions and corrections from any
one into whose hands the book may come.

                                                            B. F. KAUPP.

 THE NORTH CAROLINA STATE COLLEGE OF AGRICULTURE,
                 WEST RALEIGH, NORTH CAROLINA,
                       _September, 1918_.




                                CONTENTS


                               OSTEOLOGY

                                                                 PAGE
  OSSEOUS STRUCTURE                                                17
  CLASSIFICATION OF BONES                                          20
  COMPOSITION OF BONE                                              21
  SKELETON OF THE FOWL                                             21
      Axial Skeleton                                               23
          Cranium and Face                                         23
              Occipital                                            25
              Ethmoid                                              27
              Sphenoid                                             28
              Frontal                                              29
              Parietal                                             29
              Temporal                                             29
              Premaxilla                                           31
              Maxilla                                              32
              Nasal                                                32
              Lacrimal                                             32
              Palatine                                             33
              Pterygoid                                            33
              Zygomatic                                            33
              Vomer                                                33
              Jugal and Quadrato-jugal                             33
              Quadrate                                             34
              Inferior Maxilla                                     34
              Turbinate Bones                                      34
              Hyoid                                                35
          Vertebral Column                                         35
              Cervical Vertebræ                                    35
              Atlas                                                37
              Axis                                                 37
              Dorsal Vertebræ                                      39
              Lumbo-sacral Vertebræ                                39
              Coccygeal Vertebræ                                   41
              Ribs                                                 41
              Sternum                                              42
      Appendicular Skeleton                                        43
          Shoulder Girdle                                          43
          Fore Limb                                                44
          Pelvic Girdle                                            48
          Hind Limb                                                50

                              ARTHROLOGY
  KINDS OF JOINTS                                                  56
  MOVEMENTS OF JOINTS                                              56
  LIGAMENTOUS STRUCTURE                                            57
  LIGAMENTS OF:
      Ear                                                          58
      Jaw                                                          58
      Vertebræ                                                     58
      Ribs                                                         59
      Sternum                                                      59
      Shoulder-joint                                               61
      Elbow-joint                                                  61
      Carpal Joint                                                 62
      Finger                                                       64
      Pelvis                                                       65
      Hip-joint                                                    65
      Knee-joint                                                   65
      Tibio-metatarsal Joint                                       69
      Toes                                                         69

                                MYOLOGY
  KINDS AND STRUCTURE OF MUSCLES                                   70
  FASCIA                                                           71
  MUSCULAR NOMENCLATURE                                            71
      True Dermal Muscles                                          71
      Dermo-osseous Muscles                                        73
      Muscles of the Head                                          76
      Muscles of the Tongue                                        79
      Cervical Muscles                                             81
      Muscles of the Air Passages                                  86
          Superior Larynx                                          86
          Inferior Larynx                                          86
      Sternal Muscles                                              90
      Abdominal Muscles                                            90
      Dorsolumbar Muscles                                          92
      Coccygeal Muscles                                            93
      Costal Muscles                                               96
      Anterior Pectoral Muscles                                    99
      Pectoral Muscles                                            100
      Muscles of the Scapular Region                              101
      Muscles of the Brachial Region                              104
      Muscles of the Forearm and Hand                             105
      Digital Muscles                                             109
      Muscles of the Posterior Limb                               111
      Tibial Group of Muscles                                     117
      Muscles of the Eye                                          124
      Muscles of the Ear                                          128
  FUNCTIONS OF MUSCLES                                            128

                             SPLANCHNOLOGY
  DIGESTIVE APPARATUS                                             135
      Mouth                                                       135
      Tongue                                                      139
      Pharynx                                                     141
      Glands Adjacent to Mouth and Pharynx                        141
      Esophagus                                                   142
      Crop                                                        142
      Stomach                                                     143
          Proventriculus                                          143
          Gizzard                                                 145
      Small Intestine                                             147
      Large Intestine                                             150
      Cæca                                                        151
      Cloaca                                                      151
  COURSE OF THE FOOD                                              152
  ACCESSORY ORGANS OF DIGESTION                                   152
      Liver                                                       153
      Pancreas                                                    155
      Spleen                                                      155
  ABDOMINAL AND PELVIC CAVITIES                                   156
  PERITONEUM AND MESENTERY                                        156
  RELATIONS OF THE VISCERAL ORGANS OF THE DOMESTIC FOWL           158
  RELATIONS OF THE VISCERAL ORGANS OF THE BABY CHICK              165
  URO-GENITAL SYSTEM                                              169
      Urinary Apparatus                                           169
          Kidneys                                                 169
          Ureter                                                  174
      Male Generative Organs                                      175
          Testicles                                               175
          Vas Deferens                                            178
      Female Generative Organs                                    178
          Egg                                                     180
          Oviduct                                                 182
          Parts of the Oviduct                                    183
          Ligaments of the Oviduct                                188
  DUCTLESS GLANDS                                                 190
      Thyroid Gland                                               190
      Thymus Gland                                                190
      Adrenal Gland                                               191
  RESPIRATORY APPARATUS                                           193
      Nostrils and Nasal Chambers                                 193
      Pharynx and Superior Larynx                                 193
      Trachea                                                     194
      Inferior Larynx                                             194
      Bronchi and the Lungs                                       195
      Air-sacs                                                    199

                               ANGIOLOGY
  CIRCULATORY APPARATUS                                           206
      Heart                                                       206
          Structure of the Heart                                  207
      Blood-vessels                                               209
          Structure of the Capillaries and Arteries               209
          Structure of the Veins                                  211
      Arterial Trunks                                             211
      Branches of:
          Arteria Brachiocephalica                                213
          Arteria Carotis Cerebralis Interna                      214
          Arteria Carotis Externa                                 214
          Arteria Carotis Facialis                                214
          Aorta Posterior                                         224
      Venous Trunks                                               233
      Branches of:
          Venæ Cavæ Anteriores                                    234
          Vena Jugularis                                          237
          Vena Occipitalis Externa                                239
      Venous Sinuses of the Head                                  239
      Veins of the Brain Cavity                                   241
      Veins of the Neck                                           242
      Branches of the Vena Subclavia                              243
      Veins of the Dorsal Region                                  243
      Veins of the Thorax                                         244
      Veins of the Fore Limb                                      245
      Branches of the Iliaca                                      246
      Branches of the Vena Iliaca Interna                         247
      Posterior Vena Cava                                         247
      Veins of the Posterior Extremity                            248
      Branches of the Vena Cava Posterior                         248
      Veins of the Caudal Region and Pelvic Cavity                250
      Veins of the Truncus Vena Iliaca Communis                   252
      Visceral Veins of the Posterior Vena Cava                   252
      Lymphatic System                                            254
  BLOOD AND ITS FUNCTIONS                                         257
  FATE OF THE ERYTHROCYTE                                         261

                               NEUROLOGY
  NERVOUS SYSTEM                                                  264
      Cranial Nerves                                              265
          Olfactorius                                             265
          Opticus                                                 267
          Motoris Oculi                                           267
          Patheticus                                              268
          Trifacialis                                             268
          Abducentes                                              270
          Facialis and Acousticus                                 271
          Vagus Group                                             272
          Glosso-pharyngeus                                       272
          Vagus or Pneumogastricus                                273
          Accessorius Spinalis                                    274
          Hypoglossus                                             274
      Spinal Cord                                                 275
          Structure of the Cord                                   275
          Structure of the Nerve Trunks and Ganglia               277
          Spinal Nerves                                           281
          Brachial Plexus                                         282
          Lumbo-sacral or Crural Plexus                           285
      Brain                                                       288
          Coverings of the Brain                                  288
          Structure of the Brain                                  289
          Divisions of the Brain                                  290
      Sympathetic Nervous System                                  297
      Functions of the Nervous System                             300

                             ESTHESIOLOGY
  SENSE ORGANS                                                    303
      Sight                                                       303
      Hearing                                                     305
      Smell                                                       307
      Taste                                                       307
      Touch                                                       307
  STRUCTURE OF APPENDAGES                                         309

                              EMBRYOLOGY
  SPERMATOGENESIS                                                 318
  OÖGENESIS                                                       319
  FERTILIZATION                                                   319
  OUTLINE FOR LABORATORY STUDY OF THE CHICK                       330
      Living Embryo                                               330
      Preparation for Study of Entire Embryos and Sections        330
      Points to be Observed in the Study                          332
  DERIVATIVES OF THE GERM-LAYERS                                  342
  PREPARATION OF STRUCTURES FOR STUDY                             343
      Directions for Dissecting Muscles                           343
      Directions for Study of the Viscera                         344
      Directions for Study of the Arteries                        345
      Study of the Structure of Bones                             346
      Special Technic for Dissection of Cranial and Spinal
        Nerves                                                    347
      Directions for Study of Soft Structures                     347
      To Stain Sections of Liver for Study of Kupffer Cells       349
      To Prepare Anatomical Specimens for Museum                  349
      To Make Specimens Transparent                               350
  EQUIPMENT FOR THE DISSECTION LABORATORY                         351

  BIBLIOGRAPHY                                                    353
  ───────────────────────────────────────────────────────────────────
  INDEX                                                           355




                                ANATOMY
                                 OF THE
                             DOMESTIC FOWL




                               OSTEOLOGY


=Osseous Structure.=—Bone is structurally modified connective tissue
which has become hard by being impregnated with calcium salts.

_Kinds of Bone Tissue._—There are two kinds of bone tissue: substantia
compacta, or compact bone tissue; and substantia spongiosa, or spongy,
cancellous bone tissue.

_Compact Bone Tissue._—The compact bone tissue forms the hard outer
layer of all bones. It is thickest in the shaft and becomes thin toward
the extremities. Through the compact bone tissue approximately parallel
with the longitudinal axis of the bone, run canals called _Haversian
canals_, through which pass blood and lymph vessels for the nourishment
of the bone and nerves. The Haversian canals are surrounded by
_concentric lamellæ_. The spaces between the cylinders thus formed are
filled with _interstitial lamellæ_; and both the exterior surface of the
bone and the interior surface surrounding the medullary canal, are built
up of peripheral, or circumferential lamellæ. Between the lamellæ,
somewhat irregularly placed, are minute reservoirs, called _lacunæ_,
which contain bone corpuscles. From the lacunæ radiate minute canals, or
_canaliculi_, which maintain circulation through the bone substance, and
which communicate with the Haversian canals. Complex anastomoses exist
among the canaliculi. Still other channels for the passage of
blood-vessels are Volkmann’s canals which pierce the peripheral lamellæ,
thus allowing vessels to pass from the periosteum to the Haversian
canals. Similar channels afford communication between the inner
Haversian canals and the medullary cavity.

The entire structure composed of an Haversian canal, its surrounding
lamellæ, lacunæ, and canaliculi, with their contained vessels, is called
an _Haversian system_.

_Cancellous Bone Tissue._—The cancellous bone tissue forms the bulk of
the short, flat, and irregular bones and of the extremities of the long
bones. It consists of delicate bony plates and spicules, which
intercross in various directions. The spaces between these plates and
spicules, called _cancelli_, are occupied by marrow except in the bones
that are pneumatic. The blood-vessels, lymphatics, and nerves course
through this marrow but are not arranged in an Haversian system.

[Illustration:

  FIG. 1.—Longitudinal section of compact bone of the femur of the hen.
    1, Haversian canals. 2, Lacunæ with their canaliculi.
]

_The Periosteum._—Covering the surface of bone, except at the articular
surface where it is covered with cartilage, is a membrane, the
periosteum, which consists of two layers: an outer, fibrous, protective
layer, and an inner, cellular, osteogenic layer. The outer layer
consists principally of white fibrous tissue. The inner layer contains
many more connective-tissue cells, which gradually become more closely
aggregated as we proceed toward the osseous surface; but there is no
sharply defined line of demarcation between the two periosteal layers.

[Illustration:

  FIG. 2.—Transverse section of compact bone of the femur of the hen. 1,
    The lacunæ and canaliculi. 2, The periosteum.
]

[Illustration:

  FIG. 3.—Transverse section of compact bone of the femur of the hen
    showing the lacunæ and canaliculi under high magnification.
]

The periosteum is firmly attached to the bone by trabeculæ of fibrous
tissue, called the _fibers of Sharpey_. These fibers of Sharpey
penetrate the bone at right angles to its surface and carry
blood-vessels.

_Marrow._—There are two kinds of marrow: yellow, or medulla ossium
flava, and red, or medulla ossium rubra.

The _yellow marrow_ occurs in all bones except the femur and proximal
portion of the tibia of adult fowls. It is composed of a network of
fibrous tissue carrying blood-vessels, fat cells, and myelocytes, or
marrow cells.

The _red marrow_ is found throughout the femur and the proximal portion
of the tibia, and in a few of the pelvic bones and vertebræ in the adult
fowl, and in certain other bones of the baby chick. Red marrow consists
of a delicate network of connective tissue supporting a dense capillary
plexus, a small amount of fat, and numerous cells. The cellular elements
of red marrow consist of marrow cells which contain large nuclei and
possess ameboid movement, red blood cells, giant cells containing one or
more nuclei, and various kinds of leucocytes, including eosinophiles,
mast cells, and also osteoclasts.

_Growth of Bone._—In the baby chick, only the shaft and a portion of the
extremities of the long bones are thoroughly ossified, the extreme ends,
and of the femur most of the articular head, being cartilaginous. The
bones grow in length by an increase in the cartilage, the cartilage
gradually becoming ossified. Growth in diameter is accomplished by the
constant deposition of new layers of bone beneath the periosteum. During
this process the osteoclasts absorb the bone from within. The formation
of the marrow cavity is thus effected.


=Classification of Bones.=—The bones of the fowl are classified as long,
short, flat, and irregular.

_Long Bones._—The long bones occur in the legs and wings, where they
serve as levers to sustain weight and make locomotion possible. A long
bone consists of a shaft and two extremities. The superior is called the
_proximal_ and the inferior the _distal extremity_. The expanded
articular surfaces in forming joints with adjoining bones afford ample
space for the attachment of ligaments. The shaft is cylindrical and
hollow.

_Short Bones._—Short bones occur in the feet and in the wings. Their
structure is similar to that of the long bones.

_Flat Bones._—The flat bones occur where extensive protection is needed,
as in the cranial region; or where large surface for muscular
attachments is needed, as in the costal and pelvic regions. Flat bones
are made up of two thin layers of compact bone with a variable amount of
cancellous tissue interposed.

_Irregular Bones._—The irregular bones include the vertebræ, the
patellæ, and the carpal bones.


=Composition of Bone.=—Bone consists of organic and inorganic matter.
Organic matter gives toughness and elasticity to the bone, and inorganic
matter hardness. The organic substance of bone is called ossein. When
boiled in water ossein is resolved into gelatin. The following tables[1]
give the results of an analysis of the femur, fresh, of a mature hen.

Footnote 1:

  Grateful acknowledgment is hereby made to Dan M. McCarty, Chemist,
  Animal Industry Division, North Carolina Agricultural Experiment
  Station, for this analysis.

 Fresh femur:
        Water                                            18.23 per cent.
        Dry matter                                       81.77 per cent.
 Dry matter:
        Organic matter                                       63.09 parts
        Inorganic matter                                     18.68 parts
 Salts in dry matter:
        Calcium                                          6.970 per cent.
        Magnesium                                        0.283 per cent.
        Potassium                                        0.004 per cent.
        Sodium                                           0.276 per cent.
        Iron                                             0.020 per cent.
        Phosphorus                                       3.210 per cent.
        Sulphur                                          0.085 per cent.
        Chlorine                                         0.520 per cent.
        Carbon dioxid                                    0.550 per cent.

The inorganic matter of the femur of the hen consists of 18.68 parts or
22.84 per cent. of dry matter, and the organic matter of 77.16 per cent.
Stated in other words the femur, including its contained marrow,
consists of organic and inorganic matter in the ratio of 3.4,
approximately, to 1.


=The Skeleton of the Fowl.=—The skeleton of a bird is remarkable for the
rapidity of its ossification. It is worthy of note that other parts of
the bodies of adult birds also become ossified. Among such parts are the
tendons of the muscles of the legs, of the feet, and of the neck; the
plates of the corneal margin of the sclerotic tunic of the eye; and the
stapes of the ear. Ossification in birds at the attachments of the
semi-lunar valves of the aorta and of the pulmonary artery has been
reported by Owen.

The bony structure is compact, and the bones contain a greater
proportion of phosphate of lime than do the osseous structures of
mammals. Especially is this the case in those parts of the skeleton
which are permeated by air.


                     THE DIVISIONS OF THE SKELETON

                     ( The Skull ( Cranium
                     (           ( Face
  The Axial skeleton (                      ( Cervical region
                     (                      ( Dorsal region ( Ribs
                     ( The Vertebral column (               ( Sternum
                                            ( Lumbar region
                                            ( Sacral region
                                            ( Coccygeal region

                                              ( Scapula
                            ( Shoulder girdle ( Coracoid
                            (                 ( Clavicle
                            (
                            (           ( Arm ( Humerus
                            (           (
                            ( Fore limb ( Forearm ( Radius
                            (           (         ( Ulna
                            (           (
                            (           (      ( Carpus
  The Appendicular skeleton (           ( Hand ( Metacarpus
                            (                  ( Phalanges
                            (
                            ( Pelvic girdle ( Ilium
                            (  (Hip bone)   ( Ischium
                            (               ( Pubis
                            (
                            (           ( Thigh ( Femur
                            ( Hind limb (
                                        ( Leg ( Tibia
                                        (     ( Fibula
                                        (
                                        ( Foot ( Metatarsus
                                               ( Phalanges

The bodies of birds contain many air reservoirs to make them light that
flying may be more easy. Many bones have their weight in proportion to
size and strength thus greatly reduced. In very young birds the cavities
of bones contain, instead of air spaces, loosely arranged red marrow,
which is in most bones later absorbed. The air reservoirs in bones are
most capacious in the best flyers. In the non-flyers more of the bones
retain their red marrow.

The bones supplied with air spaces are relatively larger than in
mammals, and are provided with small transverse osseous columns which
cross in different directions and from side to side. These cross beams
give stability to the thin wall of the bone. The membranes lining these
cavities are very vascular.


                           THE AXIAL SKELETON


                               THE SKULL

The skull is divided into the cranial and facial portions. In these
parts we find present 31 bones: one occipital, two parietal, two
frontal, one ethmoid, one sphenoid, and two temporal; all of which
constitute the cranial group; two premaxillary, two maxillæ, two nasal,
two lacrimal, two palatine, two pterygoid, two zygomatic, one vomeral,
the two jugal, and two quadrato-jugal, which constitute the facial
group; two quadrati and one inferior maxillary, which constitute the
inferior jaw group.

The peculiarities of the skull are the long os incisivum and the single
condyle located on the occipital bone just below the foramen magnum. The
condyle articulates with the atlas.

The head of the bird is small in proportion to the size of the body, and
in front it is conical in shape.


                              THE CRANIUM

The cranial cavity, or cavum cranii, incloses the brain with its
membranes and vessels.

The dorsal wall, or roof, is formed by the frontal and the parietal
bones. In the median line of the cerebral portion is the internal
parietal crest. The roof of the cerebellar portion is marked centrally
by a groove.

The posterior wall of the cerebellum is formed by the occipital bone.

The lateral wall is formed chiefly by the temporal bone. It is marked by
a ridge which divides the cavity into the cerebral and cerebellar
compartments. The cerebral portion is marked by a depression which
receives the optic lobes. A crest divides this cavity from the optic
portion. The walls are marked by digitations and vascular grooves.

[Illustration:

  FIG. 4.—The skeleton of the domestic fowl. 1, Os incisivum. 2,
    External nasal opening. 3, Os nasale. 4, Os lachrymale. 5, Lamina
    perpendicularis. 6, Os dentale. 7, Os palatine. 8, Os
    quadrato-jugal. 9. Os pterygoideum. 10, Os quadratum. 11, Os
    articulare. 12, External auditory canal. 13, Atlas. 14, Os carpi
    radiale. 15, Radius. 16, First finger. 17, Os metacarpus. 18, Second
    finger. 19, Third finger. 20, Os carpi ulnare. 21, Ulna. 22,
    Humerus. 23, Thoracic vertebræ. 24, Scapula. 25, Os ilium. 26,
    Foramen ischiadicum. 27, Caudal vertebræ. 28, Pygostyle. 29, Foramen
    obturatum. 30, Os ischium. 31, Processus uncinatus. 32, Vertebral
    rib. 33, Os claviculum or furculum. 34, Os coracoideum. 35, Os
    femoris. 36, Os pubis. 37, Body of sternum. 38, Lateral internal
    process of sternum. 39, Costal process of sternum. 40, Sternal
    crest, cristi sterni, or keel of breast-bone. 41, Sternal rib. 42,
    Lateral external process of sternum. 43, Os fibula. 44, Xyphoid
    process of sternum. 45, Internal notch. 46, Os patella. 47, Os
    tibia. 48, Os metatarsus. 49, Second toe. 50, Fourth toe. 51, Os
    metatarsale. 52, First toe. 53, Second toe. 54, Second phalanx of
    second finger. 55, Os metacarpus. 56, Air opening in humerus. 57,
    Hypocledium. 58, External notch. 59, Cervical vertebræ. 60, Foramen
    oblongum.
]

The ventral wall, floor, or basis cranii interna, may be regarded as
forming five fossæ. These are: one anterior, one middle, one posterior,
and two lateral. The _anterior fossa_ supports the frontal and olfactory
parts of the cerebrum. It lies at a higher level than the middle fossa.
The _middle fossa_, or _fossa cranii media_, is circular in outline and
extends into the lateral fossæ which lodge the olfactory lobes. Just
back of the middle fossa is the sulla turcica, upon which rests the
pituitary body. The _posterior fossa_, or _fossa cranii posterior_,
lodges the medulla oblongata.


=Bones of the Cranium= (Figs. 4, 6, 7, and 8).—The bones of the cranium
fuse early in the chick’s life. The sutures uniting the bones can
usually be seen in the fetus or in the baby chick soon after it emerges
from the shell. The major portion of the cranial bones become entirely
fused. Each cranial and each facial bone ossifies from a distinct center
or centers.

The cavity for the cerebrum is much larger than the cavity for the
cerebellum. The cranial cavities in birds are relatively larger than in
mammals. The bones are designated as in mammals. There are three single
bones, the occipital, the ethmoid, and the sphenoid. Those in pairs are
the frontal, the parietal, and the temporal.


=The Occipital.= _Location._—The occipital bone or os occipitale, is
situated at the posterior part of the cranium, of which it forms the
posterior wall. This part is called the base of the cranium. The
occipital bone articulates with or touches inferiorly, the sphenoid,
laterally, the temporal, and superiorly, the parietal.

_Development._—The occipital bone is developed from four centers of
ossification; the dorsal, or os occipitale superius, two lateral, or
ossa occipitales laterales, and the ventral, or os occipitale inferius,
all of which may be seen distinct in the baby chick (Fig. 5, Part II,
No. 1).

[Illustration:

  FIG. 5.—Bones of the head and vertebra.

  Part I.—1, The cranium. 2, The skull cap. 3, The ethmoid bone. 4, The
    inferior maxilla. 5, The palatine bone. 6, The quadrato-jugal. 7,
    The jugal. 8, The superior maxilla. 9, The premaxilla. 10, The horny
    covering for the premaxilla. 11, The horny covering for the os
    dentale. 12, The os quadratum. 13, The nasal bone. 14, The
    pterygoid.

  Part II.—1, The os occipitale (1, dorsal; 2, two lateral; 3, ventral
    portions and 4, foramen magnum). 2, The fourteen cervical vertebræ.
    (1, atlas; 2, axis). 3, The seven dorsal vertebræ. 4, The fourteen
    lumbo-sacral vertebræ. 5, The seven coccygeal vertebræ. 6, The
    pelvis (1, ilium; 2, ischium; 3, pubis; 4, cotyloid cavity or
    acetabulum). 7, The vertebral column complete from the baby chick.
    8, The parietal bone. 9, The temporal bone. 10, The frontal bone.
]

_Description._—In the center of the occipital bone is the _foramen
magnum_. Through this foramen the spinal cord extends into the cranial
cavity and connects with the medulla oblongata. The occipital bone has a
single condyle, which is located just below the foramen magnum and
articulates with the atlas. At the base of the condyle a small
_subcondyloid fossa_ receives the body of the atlas during extreme
flexion of the head. In the center of the lateral wing of the occipital
bone there is a small foramen through which passes the hypoglossal
nerve. Somewhat laterally from this foramen there is an opening through
which the vagus, or pneumogastric nerve passes. Laterally from these is
the _canalis caroticus et jugularis_. Between the os occipitale
superius, or dorsal portion, and the ossa parietalia is a space to which
ligaments are attached, called the fontanel.

[Illustration:

  FIG. 6.—View of the frontal region of the skull of a hen. 1, Parietal.
    2, Frontal. 3, Nasal. 4, Premaxilla. 5, Temporal. 6, Inferior jaw.
    7, Jugal bone.
]


=The Ethmoid.= _Location._—The ethmoid, or os ethmoidale, forms the
anterior wall of the cranium, and the orbital septum. It is related
anteriorly with the vomeral, superiorly with the nasal and frontal,
posteriorly with the temporal, and inferiorly with the sphenoid, and
palatine.

_Description._—The ethmoid consists of a perpendicular and a horizontal
lamina. The perpendicular lamina, located between the orbital cavities,
is called the _septum interorbitale_. On each side of the septum
interorbitale and near the superior orbital roof are two foramina for
the passage of the olfactory nerves. In the horizontal plate, which
forms the anterior cranial wall, are located the _optic foramina_
through which pass the optic nerves.

[Illustration:

  FIG. 7.—Side view of the skull of a hen. 1, Lamina perpendicularis. 2,
    Foramen for the passage of the nerve of smell. 3, Foramen for the
    passage of the optic nerve. 4, Nasal bone. 5, External nasal
    opening. 6, Premaxilla. 7, Os dentale. 8, Superior maxilla. 9, Os
    jugal. 10, Os quadrato-jugal. 11, Os quadratus. 12, Pterygoideus.
    13, Os articulare. 14, Inferior maxilla. 15, Temporal. 16, External
    auditory canal. 17, Parietal. 18, Frontal. 19, Palatine. 20, Orbital
    process, posterior to which is the processus zygomaticus. 21,
    Interorbital foramen and optic foramen for passage of optic nerve.
    22, Attachment for inferior oblique; 23, for superior oblique; 24,
    for levator palpebræ superioris; 25, for internal rectus; 26, for
    superior rectus; 27, for external rectus; 28, for inferior rectus;
    28, for inferior rectus; 29, for depressor palpebræ inferioris; 30,
    for orbicularis palpebrarum; 31, for tensor tympani; 32, for
    circumconcha.
]


=The Sphenoid.= _Location._—The sphenoid, or os sphenoidale, forms the
floor of the cranial cavity and articulates with or touches posteriorly
the occipital, laterally the temporal, and anteriorly the palatine, and
ethmoid.

_Description._—The sphenoid bone, the largest part of the cranial floor,
is formed by the fusion of the nasal and the cranial parts. It is a
three-cornered bone with two, thin, broad wings. These wings are divided
into two portions, orbital wings, or _alæ orbitales_, and temporal
wings, or _alæ temporales_. The temporal wing forms a cover for the
Eustachian tube trumpet, and for the canal coming from the sella
turcica, which latter gives passage to the intracranial carotid artery.
The orbital wing forms the lower portion of the posterior wall of the
orbital cavity, and lies directly before the os petrosum or temporal
bone where the second and third branches of the fifth pair of cranial
nerves emerge from the cranial cavity.

Anteriorly the sphenoid has a foramen for the passage of the Eustachian
tube, the _tuba auditiva_, and also a sharp-pointed projection, the
nasal portion, called the _rostrum_.


=The Frontal.= _Location._—The frontal bones, or ossa frontales, two in
number, form the forehead, a portion of the nose, and a portion of the
roof of the orbital cavities. They are related posteriorly with the
parietal, laterally with the temporal and zygomatic, and anteriorly with
the nasal and premaxillary. They touch inferiorly the ethmoid.

_Description._—Each of these bones has a _processus orbitalis_ which is
seen at the outer margin of the posterior and upper orbital wall and
just in front of the zygomatic process of the squamous portion of the
temporal. The frontal bone forms the anterior portion of the superior
wall of the cranial cavity. The two bones are thin, flat, and meet at
the median line of the forehead. The external surface is convex. The
inner surface has a ridge located longitudinally and in the center the
bone becomes narrow anteriorly.


=The Parietal.= _Location._—The parietal bones, or ossa parietalia, two
in number, form the posterior part of the roof of the cranial cavity.
They meet in the median line and are related posteriorly with the
occipital, anteriorly with the frontal, and laterally with the temporal
bones.

_Description._—The parietal bones are short and very broad (Fig. 5, Part
II, No. 8). Each bone is quadrilateral in outline and has two surfaces,
four borders and four angles. The external parietal surface is convex
and smooth and the internal, cerebral surface is concave.


=The Temporal.= _Location._—The temporal bones, or ossa temporales, two
in number, are located at the lateral portion of the cranium, and aid in
the formation of the cranial wall. The temporal bone is related
posteriorly with the occipital, superiorly with the parietal and
frontal, externally with the quadratus, anteriorly with the ethmoid, and
inferiorly with the sphenoid.

_Description._—The temporal bones consist of the fused squamous and
petrous temporals; they contain the essential organs of hearing.

[Illustration:

  FIG. 8.—Inferior view of the skull of a hen. 1, Occipital. 2, Foramen
    magnum. 3, Occipital condyle and just below the basi-occipital. 4,
    Foramen for the passage of the hypoglossal nerve. 5, Foramen for the
    passage of the vagus. 6, Canalis caroticus and jugulare. 7,
    Sphenoid. 8, Temporal wings of the sphenoid. 9, Foramen auditiva.
    10, Os articulare. 11, Os angulare. 12, Vomer. 13, Os dentale. 14,
    Pterygoid.
]

The _squamous portion_ of the temporal bone possesses the long thin
zygomatic process sometimes called the _posterior orbitalis_. It forms a
small flattened tongue, directed forward, sometimes free, and at other
times united by its superior border to the summit of the orbital
process. This is especially true in the turkey. This process is seen
near the lower outer portion of the posterior orbital wall. The squamous
portion is also provided antero-laterally with an articular facet which
articulates with the quadrate bone. The large portion of the temporal
bone lies on the side of the cranium superior to the ala sphenoida
temporale. It extends outward and anteriorly over the rims of the
petrosum and ala sphenoida orbitale. The squamous part forms the upper
three-fourths of the cochlea, the inner auditory canal, the upper part
of the fenestra ovalis, the anterior vertical and the outer semicircular
canal, and the lower part of the posterior vertical semicircular canal.

The _petrous portion_ forms the posterior wall of the foramen ovale and
the fenestra ovalis in which lies the columella. The fenestra ovalis and
the fenestra rotunda are the only two entrances into the labyrinth. In
this region may be seen the fusion line between the os petrosum and the
os occipitale. Superiorly and posteriorly the petrous portion touches
the external parietalia and occipitalis; infero-laterally it unites with
the basi-sphenoid. The outer rim of the foramen ovale is broadened by
the ala sphenoida and mesially by the basi-sphenoid. This foramen gives
exit to the second and third divisions of the fifth pair of cranial
nerves.

The lateral surface of the temporal bone presents a short tube, the
_external acoustic process_, or _processus acusticus externus_, to which
is attached the concha of the ear. The process is directed outward. Its
lumen, the _external acoustic meatus_, or _meatus acusticus externus_,
conducts to the cavity of the middle ear in the bare skull, but is
separated from it by the tympanic membrane in the natural state.


                           BONES OF THE FACE

The bones of the face, or ossa faciei, are the premaxillary, or upper
mandible, the maxillæ, the nasal, the lacrimal, the palatine, the
pterygoid, the zygomatic, the vomeral, the jugal and the quadrato-jugal.
The vomer is single, the others are paired. In the inferior maxillary
group there are the quadrati, and the inferior maxillary, or lower
mandible. The turbinated and hyoid bones are also discussed with the
bones of the face.

The beak consists of the anterior portion of the upper and lower
mandibles which are covered with a horny structure.


=The Premaxilla.= _Location._—The premaxillæ, or ossa incisiva, or
mandibular structures, are located in the extreme anterior facial
region.

_Description._—The premaxillæ are long and the anterior end is pointed.
Each consist of two lateral halves which become fused before the chick
is hatched. They partly circumscribe the openings into the nose. This
bone is the base of the upper portion of the beak and determines its
form. It forms the anterior walls of the nasal cavity. It has between
the nasal bones, two processes which extend back to the anterior point
of the cerebral cavity. The posterior part of the incisivum and nasale
are flat, thin, and elastic. The extensions then are the _processus
maxillaris_, the _processus palatinus_, and the _processus frontalis_,
the first of which forms part of the jaw rim, the second, which aids in
forming the gum plate, and the last which reaches to the anterior
portion of the cranial wall.


=The Maxilla.= _Location._—The superior maxillaries, or ossa maxillares,
two in number, form the floor of the upper beak, a part of the palatine
roof and nasal walls.

Each maxilla borders laterally the premaxilla and the nasal; inferiorly,
the anterior point of the palatine; and posteriorly, the jugale.

_Description._—The maxillæ are thin, flat, bones. They have three
borders and three angles. The palatine processes of the two bones do not
meet in the median line, which results in a cleft in the median palatine
region. The bone-like gums are formed partly by the palatine processes
but more largely by lateral wings of the os incisivum. Each maxilla has
posteriorly a yoke-like extension, superiorly a small extension, and
also a palatine process. The latter articulates by a facet with the
vomer.


=The Nasal.= _Location._—The nasal bones, or ossa nasalia, two in
number, are located in the lateral facial region. The nasal bone
articulates posteriorly with the frontal; laterally, on the inner
border, with the processus frontalis of the premaxilla, and on the outer
border with the lacrimal; and inferiorly with the premaxilla, maxilla,
jugale, and vomer.

_Description._—The nasal bone, or os nasale, is broad, flat, and elastic
and forms the posterior wall of the nasal opening. Under this bone is
located the infraorbital sinus.

There are three extensions: first, the _processus intermaxillaris_,
which forms the upper wall of the nasal cavity; second, the _processus
maxillaris anterior_, directed downward and forward, which fuses with
the maxillary bone and forms the posterior rim of the nasal cavity; and
third, a _posterior processus frontalis_, which lies parallel with the
ethmoid.


=The Lacrimal.= _Location._—The lacrimal bones, or ossa lacrimalia, two
in number, are located at the outer border and at the junction of the
processus frontalis of the nasal, with the frontal bone.

_Description._—The lacrimal bone is small, and rather filiform. They
become fused with the nasal and the frontal bones, forming part of the
margin of each.


=The Palatine.=—_Location._ The palatine bones, or ossa palatina, two in
number, enter into the formation of the inner part of the bony gum and
hard palate, or roof of the mouth. They form the support for the hard
palate. Each palatine articulates posteriorly with the rostrum, or nasal
portion of the sphenoid, and with the pterygoid; and anteriorly with the
maxilla.

_Description._—The palatine bone is curled posteriorly and is thin at
the upper portion and thick at the lower border. Anteriorly it has a
long rather filiform projection.


=The Pterygoid.= _Location._—The pterygoid bones, or ossa pterygoidea,
two in number, are located back of the region of the posterior nares.
They extend diagonally outward and backward from the median region of
the sphenoid rostrum to the quadrate bone. They articulate anteriorly
with the sphenoid rostrum and the palatine, and posteriorly with the
quadrate.

_Description._—The pterygoid bones are slender and cylindrical, and are
expanded at the ends into an articular facet.


=The Zygomatic.= _Location._—The zygomatic, or ossa zygomatica, two in
number are situated below the orbital cavity and extend from the maxilla
to the quadrate bone.

_Description._—The zygomatic is small, slender, rod-shaped, and forms
the lateral portion of the upper jaw. The anterior portion of the
zygomatic represents the jugal and is fused with the maxilla and with
the anterior processus maxillaris of the nasal bone, the maxilla, and
the posterior portion, the quadrato-jugal, which articulates with the
quadrate bone.


=The Vomer.= _Location._—The vomer is located in the median nasal
septum. It articulates with the rostrum of the sphenoid, being connected
to it by a mass of ligaments. It touches anteriorly the posterior
portion of the maxilla.

_Description._—The vomer is a median bone and aids in the formation of
the septum nasi. It consists of a thin plate, thickest posteriorly and
diminishing toward the anterior edge.


=The Jugal and Quadrato-jugal.=—The jugal and quadrato-jugal are united
forming a long slender cylindrical bone called the zygomatic, lying at
the outer side of the upper jaw. They have been described under
zygomatic, which see.


=The Quadrate.= _Location._—The quadrate bones, or ossa quadrata, two in
number, are located antero-laterally to the temporal bones. Each
articulates inferiorly with the posterior articular portion, or pars
articulare, of the inferior maxilla and infero-laterally with the
quadrato-jugalare portion of the zygomatic. It articulates
antero-internally with the pterygoid and supero-posteriorly with the
temporal.

_Description._—The quadrate bone is anvil-like in shape. It has an
anterior process, the orbital process, for muscular attachments, and
posteriorly it affords attachment to the ear drum.


=The Inferior Maxilla.= _Location._—The inferior maxilla, lower jaw, or
os maxillare inferius, also called the mandibular bone, or pars dentis,
is analogous to the lower jaw of mammals. It articulates posteriorly
with the quadrate bone.

_Description._—The inferior maxilla is the largest bone of the face. It
is made up of a _right_ and a _left limb_ which are separate in the
fetus and which unite subsequently anteriorly, forming the inferior
portion of the beak. Each limb of the jaw is developed from five
elements: the _pars articularis_, which forms the jaw-joint and,
expanded, articulates with the quadrate bone; the _pars angularis_,
lying just in front of the pars articularis; the _pars supra-angularis_,
a slender bone lying just above the angularis; the _splenial_, a thin
plate of bone, lying along the inner surface of the mandible; and the
_pars dentalis_, which forms the anterior portion of the jaw.


=The Turbinate Bones.= _Location._—The turbinate bones, or ossa
turbinata, six in number, are attached to the lateral walls of the nasal
cavity (Fig. 26, No. A, 1 and 2). In each nasal cavity there are three
turbinate bones, one anterior and two posterior. Of the two posterior
the upper one lies supero-posterior to the inferior one. The turbinate
bones are attached to the lateral nasal walls, project into the cavity
and thus greatly diminishing its extent.

_Description._—Each turbinate bone is composed of a very thin lamina,
finely cribriform in many places, and in the fresh state, covered on
both sides with mucous membrane. These bones are curled and partly
membrano-cartilaginous structures which give greater surface in the
nasal passage for mucous membrane in which the olfactory nerve terminal
filaments are distributed.


=The Nasal Cavity.=—The nasal cavity, or cavum nasi, is a longitudinal
passage which extends through the upper part of the face. It is divided
into right and left halves by a median septum nasi. Its walls are made
up of the premaxilla, maxilla, nasal, vomer, and palatine bones.


=The Hyoid Bone.= _Location._—The hyoid bone, or os hyoideum, is
situated chiefly between the rami of the mandible, but its upper part
extends around the outer margin of the base of the skull. The hyoid bone
does not articulate with any bones of the skull, but is firmly attached
by strong fibrous structure.

_Description._—The hyoid bone consists of the following parts: the
_body_, or _basi-hyal_, which is subcylindrical and presents in front a
trochlear articular surface, convex transversely, and concave vertically
for articulation with the ewer-shaped portion of the glosso-hyal. The
anterior free portion, or lingual process, is called the _glosso-hyal_,
or _entoglossal bone_. The lingual process gives support to the muscular
and fibrous structures of the tongue. On either side of the basi-hyal
there is a limb passing posteriorly along the side of the superior
larynx, extending upward along the outer border of the occipital bone.
This is the _cornu_ of the os hyoideum and is divided into two elements,
first, the _basi-branchial_ which is bone and articulates with the
basi-hyal, and the second, the _cerato-branchial_, cartilaginous in
structure. In the center and projecting backward from the body of the os
hyoideum is a spur process called the _uro-hyal_, partly bony and partly
cartilaginous, and which rests upon the superior larynx.


                          THE VERTEBRAL COLUMN

The vertebral, or spinal column consists of 42 bones, as shown in the
following table:

                         Cervical region     14
                         Dorsal region        7
                         Lumbo-sacral region 14
                         Coccygeal region     7
                                             ——
                                Total        42

Many of the bones of the dorsal and lumbo-sacral regions do not have
free articulations. The cervical and coccygeal alone have free
movements.


=The Cervical Vertebræ= (Fig. 4, No. 59; Fig. 5, Part II, No. 2).
_Location._—The cervical vertebræ form the neck of the fowl.

[Illustration:

  FIG. 9.—Os hyoidum and tongue muscles. 1, Glosso-hyal. 3, Basi-hyal.
    4, Basi-branchial element of the cornua. 5, Cerato-branchial element
    of the cornua. 6, Uro-hyal or spur process. 7, Genio-hyoideus. 8,
    Cerato-hyoideus showing the slender tendon. 9, Hyoideus transversus.
    10, Hyoideus transversus.
]

_Description._—The long cervical section of the spinal column is
S-shaped and is made up of fourteen vertebræ. The anterior segments move
freely forward, the middle ones backward and the posterior ones forward,
allowing the S-shaped curve of the neck. The neck is flexible so that it
is possible for the beak to reach the coccygeal oil gland. The bird is
enabled to reach the feathers on all parts of the body to cleanse and
oil them.


=The Atlas.= _Location._—The first cervical vertebra is called the
atlas. Anteriorly it articulates with the single condyle of the
occipital bone. Posteriorly it articulates with the axis, or second
cervical vertebra.

_Description._—The atlas is the smallest of the cervical vertebræ and is
ring-shaped. The anterior articular surface, half-moon in shape, forms a
deep articular cavity. The joint, called a ball-and-socket joint, makes
possible movements in all directions. The condyle of the occiput also
touches an articular end of the odontoid process of the axis, or second
cervical vertebra. Posteriorly there projects from the atlas two small
lateral wings possessing articular facets which articulate with similar
facets on the lateral wings of the axis. Posteriorly the body of the
atlas is also provided with an articular surface which articulates with
a similar surface on the anterior portion of the body of the axis.


=The Axis.= _Location._—The axis is the second cervical vertebra. It
articulates anteriorly with the atlas, and by a facet on the extreme
anterior end of the odontoid process, with the condyle of the occipital
bone. Posteriorly it articulates with the third cervical vertebra.

_Description._—The body of the axis is short. The upper anterior portion
of the body of the axis is provided with a tooth-like process called the
_odontoid process_. There are two anterior lateral wings provided with
small articular facets which articulate with similar facets of the
atlas. The anterior surface of the body of the axis forms a true
articulation with the body of the atlas.

The axis is provided with a _superior_ and an _inferior spine_. There
are two posterior articular processes which articulate with the
prezygapophyses, or anterior articular processes, of the third cervical
vertebra. The posterior part of the body of the axis forms a true
articulation with the body of the third cervical vertebra.


=Other Cervical Vertebræ.=—Beginning with the axis, the body of which is
relatively short, the body of each succeeding vertebra is longer than
that of the preceding. The articulations of each vertebra with adjoining
vertebræ are effected by means of diarthrodial facets, convex in one
direction and concave in the other.

[Illustration:

  FIG. 10.—_A._ Diagram of three first dorsal vertebræ and scapular
    arch-side view. _B._ Diagram of section through the hemal arch.

  _A._ 1, First dorsal segment. 2, Second. 3, Third. 4 and 5, Hemal
    arches. 6, The pleurapophyses or floating ribs. 7, The third
    pleurapophyses or dorsal vertebral rib articulating with the
    hemapophysis or sternal rib, 8, and this in turn with the wing of
    the sternum form a hemal arch. 9, The sternum. 10, Intervertebral
    foramen through which the nerves pass. 11, Articulation with the
    body of vertebra parapophyses. 12, Articulation with transverse
    process or diapophyses. 13, Oblique process or zygapophysis. 14, The
    epipleural appendage.

  _B._ 1, Hemal or inferior spine (hypapophysis). 2, The neural arch. 3,
    The pleurapophyses or rib. 4, The superior or neural spine or
    neurapophysis which aids in the formation of the anapophyseal ridge.
    5, Parapophyseal surface for head of rib. 6, Tubercle of rib
    articulating with the diapophysis. 7, Lamina of neurapophysis. 8,
    Centrum. 9, Hemal arch.
]

Between the bodies of the vertebræ are pads of fibrous cartilage. Above
these bodies and inferior to the neural spines extends throughout the
spinal column the large _neural canal_ which is occupied by the spinal
cord. Between the vertebral segments the neural canal is exposed
superiorly, since here the neural arches do not completely bridge the
canal. These spaces are protected by intervertebral ligaments.

In addition to the superior neural spines and the inferior spines, from
the body of the vertebra project _lateral processes_, and anterior and
posterior _oblique processes_.

All cervical vertebræ except the atlas and the axis are made up of the
following parts: a body, or centrum, a neural canal, a neural arch, a
superior dorsal, or neural spine, or neurapophysis, which in most
cervical vertebræ is only slightly developed, two oblique processes, or
zygapophyses, two transverse processes, or diapophyses (Fig. 10, No. 12)
and in some vertebræ two tubercles, or anapophyses above the posterior
zygapophyses. The _prezygapophyses_ are directed upward and inward; the
_postzygapophyses_ are directed downward and outward. The inferior
spines are only well developed in the last two or three cervical
vertebræ.

Between vertebral segments, except the central sacral portion, on each
side, there is an _intervertebral foramen_ (Fig. 11, No. _A_, 4),
through which pass the spinal nerves. In the central portion of the
sacrum where the vertebræ have fused, there are two foramina on each
side for each original vertebra, one located above the other, the upper
giving passage to the sensory branch, the lower to the motor branch of
the nerve.

=The Dorsal Vertebræ= (Fig. 4, No. 23; Fig. 11, _A_). _Location._—The
dorsal, or thoracic vertebræ, or vertebræ thoracicales, aid in forming
the roof of the chest cavity.

_Description._—The dorsal vertebral section is made up of seven
vertebræ, with strong short bodies. The first and sixth dorsal segments
articulate as do the cervical, by the bodies and oblique processes.
(Fig. 11, No. _A_, 3, illustrates the oblique processes.) The seventh
dorsal is fused with the first lumbo-sacral vertebra. The second to the
fifth inclusive of the vertebræ are fused together, and the superior and
inferior spinous processes are fused into a prominent plate-like ridge.

The transverse processes of the dorsal vertebræ, from the second to the
sixth, are well developed and are bridged over with a thin layer of
bone. The ventral spines are partly fused and form a very prominent and
continuous ridge. (Fig. 11, No. _A_, 1, shows the fused superior spines;
No. 2, the fused inferior spines; and No. 4, the intervertebral
foramina.)

=The Lumbo-sacral Vertebræ= (Fig. 5, Part II, No. 4). _Location._—The
fused lumbo-sacral section of the spinal column forms the roof of the
pelvic cavity.

[Illustration:

  FIG. 11.—Bones from the scapular arch.

  _A._ Dorsal vertebra. 1, Superior spinous ridge, 2, Inferior spinous
    ridge. 3, Oblique processes. 4, Intervertebral foramina. 5,
    Articular facette for head of the rib. 6, Articular facette for
    tubercle of the rib. 7, Articular portion of the body.

  _B._ Outer surface of scapula.

  _C._ Inner surface of scapula. 1, Thin caudal end. 2, Articular head.
    4, Processus furcularis. 5, Processus humeralis. 6, Processus
    coracoideus.

  _D._ Outer surface of coracoid.

  _E._ Inner surface of coracoid. 1, The furcular tuberosity. 2,
    Articular facette for articulation with the sternum. 3, Articular
    surface for humerus and scapula.

  _F._ Outer surface of humerus and G the inner surface of the same. 1,
    Trochanteric fossa. 2, Oval articular head at proximal end. 3,
    Shaft. 4, Distal end showing articular condyles. 5, Trochanter. 6,
    Trochlea for ulna. 7, Trochlea for radius. 8, Depression or fossa.

  _H._ Section through the median plane of the humerus showing the
    delicate cross partitions illustrating provisions made for bones
    provided with air-sac extensions.
]

_Description._—The lumbo-sacral region consists of fourteen vertebræ
which are distinct in the body of the newly hatched chick, but which
become fused soon after hatching. With these vertebral segments there
are fused the last dorsal and first coccygeal vertebral segments. This
fusion is so complete that the segments are indicated only by the
intervertebral foramina on the sides through which the spinal nerves
pass, and by transverse markings on the inferior surface of the bodies.

The lumbo-sacral vertebræ, called the sacrum, and the ilia are fused.
The dorsal spines of the vertebral segments are indicated only in the
anterior portion where they are fused, forming a plate. There are no
prominent ventral spines.

=The Coccygeal Vertebræ= (Fig. 4, No. 27). _Location._—The coccygeal or
caudal vertebræ, or vertebræ coccygeæ, constitute the bones of the tail.

_Description._—There are seven coccygeal vertebræ. The last segment,
shaped like a plough share and therefore called the pygostyle, is the
largest and is supposed to have been formed by the fusion of several
original distinct segments. It supports the coccygeal oil gland and the
row of rudder feathers, or rectrices, which are arranged fan-wise.

All of the coccygeal vertebræ except the first are freely movable, thus
allowing the tail to be used as a rudder during flight. The lateral
spines are long and well developed, and the superior spines are
bifurcated, thus giving increased surface for muscular attachment. The
first coccygeal segment is fused with the last lumbo-sacral vertebra.


                               THE THORAX

The dorsal vertebræ superiorly, the ribs laterally, and the sternum, or
breast-bone inferiorly, form the skeleton of a large cavity called the
thorax. The dorsal vertebræ have been described.

=The Ribs= (Fig. 4, No. 32; Fig. 10, _A_ and _B_). _Location._—The ribs
form the lateral bony wall of the thorax, articulating superiorly with
the dorsal vertebræ.

_Description._—The ribs are arranged in order of length, the ultimate
rib being the longest. From anterior to posterior, they approach more
nearly a horizontal position. The ribs are divided into the true and the
false. The _true ribs_ articulate with the sternum. The _false ribs_ do
not touch the sternum; they are floating. The true ribs are composed of
two parts, a vertebral, or dorsal, and a sternal, or ventral. The
vertebral part, or _extremitas vertebralis_, is provided with an
articular head, or _caput costæ_; a neck, or _collum costæ_; and an
articular tubercle, or _tuberculum costæ_. The head and tubercle
articulate with the dorsal vertebra. Below the head of each rib is a
_pneumatic foramen_.

The distal extremity of the dorsal section of the rib articulates with
the proximal end of the sternal section by a diarthrodial articulation.

The articulations of the true ribs with the sternum is diarthrodial and
each articulate by two small ridges with a double sternal facet. The
first, the second, and the seventh ribs are floating, or false ribs. The
first rib articulates with the quadrate part of the last cervical
vertebra and also with the first dorsal vertebra. The seventh, the last
rib, articulates with the under side of the anterior alar part of the
ilium. This rib is situated similarly to the true ribs; but, instead of
articulating directly with the sternum, the lower end lies against the
sternal segment of the rib just anterior to it.

From the posterior edge of the second, the third, the fourth, and the
fifth ribs, and near the middle of the dorsal segment, are flat,
uncinate, bony processes which project upward and backward, overlying in
each case, the succeeding rib and giving greater surface for muscular
attachments and greater stability to the thorax.

=The Sternum= (Fig. 4, No. 40; Fig. 10, No. _A_, 9). _Location._—The
sternum, or breast-bone forms the inferior portion, or floor of the
thoracic cavity.

_Description._—The sternum is a quadrilateral, curved plate with
processes projecting from each angle and from the middle of the anterior
and posterior borders. The posterior medial projection, or
_metasternum_, is the longest, and has a tall, plate-like ridge—the
_sternal crest_, _crista sterni_—running along its ventral surface. The
crest serves the important function of increasing the bony area for the
attachment of the powerful muscles which move the wings. The anterior
medial projection, or _rostrum_, is short, and pierced at its root by an
opening from which extend two elongated, saddle-shaped depressions into
which the end of the coracoid bones are received.

The plate-like process of bone, the _posterior lateral process_, which
projects from the caudal angles of the sternum soon divides into two
parts. The shorter of these, the _oblique process_, broadens toward its
free end and covers the sternal segments of the last two ribs. The sides
of the sternum are thus provided with an external and an internal
process forming an _external_ and an _internal_ notch. These notches are
bridged over by a broad ligament, to which the muscles are attached. In
poor flyers, as the domestic fowl, these notches are large. The
posterior end of the sternum is called the _xiphoid process_ or
_processus xiphoideus_. Anteriorly the sternum is provided with lateral
external processes, the _costal processes_. The lateral borders of the
sternum are pitted by four depressions into which the sternal segments
of the ribs are received. The dorsal, or inner surface of the bone is
pierced by openings by which the air-sacs communicate with the interior.


                       THE APPENDICULAR SKELETON

The appendicular skeleton consists of the shoulder girdle, the fore
limb, the pelvic girdle, or hip bone, and the hind limb. The shoulder
girdle consists of the scapula, the coracoid, and the clavicle. The fore
limb consists of the arm, forearm, and the hand. The arm consists of the
humerus, the forearm of the radius and the ulna; and the hand consists
of the carpus, the metacarpus, and the phalanges. The pelvic girdle
consists of the ilium, the ischium, and the pubis. The hind limb
consists of the thigh, the leg, and the foot. The thigh consists of the
femur, and the leg consists of the tibia and the fibula. The foot
consists of the metatarsus and the phalanges.


                          THE SHOULDER GIRDLE

The shoulder girdle consists of the scapula, the clavicle and the
coracoid.

=The Scapula.= _Location._—The scapula (Fig. 11, _A_, _B_) lies on the
outer and superior rib surface, extending parallel with the dorsal
vertebræ.

_Description._—The scapula is a thin, sword-like bone, becoming thicker
as it approaches the shoulder-joint. The scapula expands and becomes
thin near the free end, which reaches nearly to the antero-lateral
portion of the ilium (Fig. 4, No. 24). The scapula articulates with the
coracoid. A _pneumatic foramen_ is located at the base of the acromion
process. The anterior part of the scapula is provided with an articular
head and is provided with an inner process, called the _processus
furcularis_, which lies near the furcula and coracoid. An outer stronger
_processus humeralis_ forms the posterior half of the _glenoid cavity_,
or _cavitas glenoidalis_, in which the humerus articulates and the
processus coracoideus.

=The Clavicle.= _Location._—The clavicles, commonly known as the wish
bone, are located in the anterior chest region.

_Description._—The clavicles are long, slender bones uniting below in
the _hypocledium_, a laterally flattened process. They are joined to the
upper end of the coracoid by fibrous cartilage. The hypocledium is
joined to the anterior point of the sternum by the claviculosternal
ligament. The clavicles, as united by the hypocledium, form a v-shaped
structure called the furculum, or, popularly, the wish bone.

The forks play the part of an elastic spring, whose office it is to
prevent the wings from coming toward each other during contraction of
the depressor muscles. The conformation of this bone is, therefore, like
the sternum, related to the extent and power of flight; and for this
reason it is that, in swift flyers, the two branches of the furculum are
thick, solid, widely separated, and curved like a U; while in those that
fly heavily and with difficulty, these branches are thin and weak, and
join at an acute angle. The latter formation greatly diminishes its
strength, and lessens, in a singular manner, the reactionary power of
the bony arch it represents.

=The Coracoid.= _Location._—The coracoid is located just back of the
clavicle and at the side of the entrance of the thoracic cavity. It is
the strongest bone of the shoulder girdle, extending upward, outward,
and forward. It articulates inferiorly with the sternum and superiorly
with the humerus and the scapula, and is attached to the superior end of
the furcular limb by a fibrous cartilage.

_Description._—It is thinnest in the center or shaft and broadens toward
the inferior extremity. The upper hook-like part of the coracoid forms
the fore part of the glenoid cavity, and together with the scapula and
furcula form the foramen triosseum through which passes the tendon of
the elevator muscle of the wing. The upper end flattens out into three
tuberosities, the tuberositas furcularis which is thick and to which
attaches the limb of the furcula, the tuberositas scapularis which
unites to the scapula, and the tuberositas humeralis which lies between
these and articulates with the humerus.


                             THE FORE LIMB

The bones of the fore limb are humerus, ulna, radius, carpus,
metacarpus, and phalanges.

=The Humerus.= _Location._—The humerus constitutes the arm, which, when
at rest, lies parallel to the dorsal vertebræ. It articulates superiorly
with the glenoid cavity, a shallow ball-and-socket joint, formed by the
scapula and the coracoid; and inferiorly with the ulna and radius.

_Description._—The proximal extremity of the humerus is provided with a
trochanter (Fig. 11, _G_, No. 5) and a large oval head or caput humeri,
which articulates in the glenoid cavity. The head is an elongate,
semi-oval convexity, with the long axis transverse from the radial to
the ulnar side and with the ends continued into upper and lower crests.
The upper crest of the head of the humerus is on the radial side and the
lower crest on the under side. Under this latter crest there is a
_pneumatic fossa_ (Fig. 11, _F_, No. 1), at the upper end of which there
is an opening into the bone, the _pneumatic foramen_, which brings the
air-sac into communication with the air space of the bone. The shaft, or
corpus humeris, is irregularly cylindrical and slightly S-shaped.

The proximal part of the shaft, which is expanded on the palmar side, is
concave across and convex lengthwise. The distal part is slightly
flattened. The shaft of the humerus is almost cylindrical.

The distal extremity of the humerus is provided with two articular
condyles, one of which articulates with the ulna and the other with the
radius. On the radial side of the palmar surface there is a ridge; and
on the ulnar side of the same surface there is a second ridge diverging
to the opposite tuberosity. The radial surface is a narrow, subelongate
convexity, extending from the middle, approximately, of the palmar
surface, obliquely to the lower part of the radial tuberosity. The two
_articular convexities_, or _trochlea_, at the distal end of the humerus
are bent toward the palmar aspect, the _anconal aspect_ is the side on
which the elbow is situated. The inner convexity is the larger and
articulates with the ulna. To the outside is the _processus cubitalis
humeri_. The outer articulates with the radius and is so arranged that
the radius makes a greater flexion than the ulna. At the lower end of
the humerus there is a depression which receives the anconeus of the
ulna during flexion and extension of the forearm. On the shoulder- and
elbow-joint are found grooves over which the tendons glide, at which
places sheaths are provided. This arrangement also aids in keeping the
capsular ligament in place.

=The Ulna.= _Location._—The ulna, larger than the radius, is bent and
articulates with the radius only at the ends. The two bones are bound
together by a ligamentous band. It also articulates superiorly with the
distal end of the humerus, and inferiorly with the carpus. When the wing
is folded the radius is superior and a trifle to the inner side of the
ulna.

_Description._—The proximal end is most expanded, and is obliquely
truncate for the articular excavation adapted to the ulnar tubercle of
the humerus. A short angular process behind the cavity represents the
_olecranon_, which is the _processus olecranalis coracoideus ulnæ_ to
which the ligamentum capsulare cubiti attaches. On the inner side of the
head is the internal tubercle of the ulna and on the external side the
external tubercle of the ulna. An excavation is noted on the radial side
of the proximal end for the lateral articulation of the head of the
radius. On the upper side near the articular part is located the
_sigmoid cavity_.

The shaft, or corpus ulnæ, decreases in size near the distal end. It is
slightly curved, flattened laterally with an internal and an external
ridge.

The distal end of the ulna is slightly expanded into a _trochlea_ which
is sharply convex and articulates with two free carpal bones, the
scapho-lunar, or os carpi radiale, and the cuneiform, or os carpi
ulnare. The scapho-lunar is placed on the radial side, and the
carpiulnare on the ulnar side. The distal extremity of the ulna is
provided with a _styloid process_ and on the dorsal side with a
_tubercle_.

=The Radius.= _Location._—The radius lies beside the ulna with which it
articulates at each extremity. At the inferior extremity the
articulation is rotary. It also articulates superiorly with the humerus
and inferiorly with the os carpi radiale.

_Description._—The radius, cylindrical in shape, is more slender than
the ulna.

The proximal end is expanded, subelliptical, with a concavity for the
oblique tubercle and a thickened convex border for articulation with the
ulna. This end is provided with the _tuberositas radii_.

The shaft, or corpus radii, is slender, subcompressed, and has a slight
bend upward from the ulna. A nutrient foramen occurs in this shaft.

The distal end is expanded and rather flattened with two grooves on the
anconal side for passage of tendons. For articulation with the
scapho-lunar the radius is provided with a terminal _transverse
convexity_ produced palmad, which also articulates with the ulna
laterally. There is a tuberosity on the radial side of the expansion and
inferiorly the _inferior tuberculum ossis carpi radialis_ and superiorly
a _superior tuberculum ossis carpi radialis_.

=The Hand.=—The hand is made up of the carpus, the metacarpus, and the
phalanges.

The bones of the hand are so arranged as to allow abduction and
adduction, or flexion in the ulno-radial plane, movements which are
necessary in the outspreading and folding of the wing. Thus the hand of
the fowl moves in a state of pronation, without the power of rotation.
The carpal bones are so placed between the anterior arm and metacarpus
as to reduce the abduction which is necessary to hold and extend the
wing, so that the hand or wing be in a fixed position.

=The Carpus.=—The carpus in the domestic fowl is represented by two
bones, ossa carpi, called the _scapho-lunar_, or _os carpi radiale_, and
the _cuneiform_, or _os carpi ulnare_. The scapho-lunar is the smaller
and is located between the radius and metacarpus. The cuneiform is the
larger and is located between the ulna, the radius, and the metacarpus.
The cuneiform is somewhat anvil-like in shape, being provided with a
body and two prongs.

=The Metacarpus.=—The metacarpal bones, or ossa metacarpi, two in
number, are separated at their middle portion, and consolidated at their
extremities. The upper proximal base of the metacarpus is provided with
a tubercle, the tuberculum muscularis, and externally the tuberculum
ulnare ossis metacarpi. The distal end of the metacarpal bone is
provided with a tuberculum articulare.

=The Phalanges.=—The first three fingers only are represented, and these
are rudimentary.

The first finger called the pollex or thumb, consists of but one joint.
It is located on the proximal and outer end of the metacarpal bone. It
has on its proximal end a tubercle, the tuberculum articulare.

The second finger, the best developed, consists of two phalanxes. These
are the main bones extending from the metacarpus. Each articular end is
provided with a _tuberculum articulare_.

The third finger, small, cylindrical in shape, is located at the distal
and inner side of the metacarpal bone.


=THE PELVIC GIRDLE= (Fig. 4, No. 25; Fig. 5, Part II, 6)

The pelvic girdle is made up of three bones as follows: the ilium, the
ischium, and the pubis, all of which are fused in adult life. They are
separate in the baby chick (Fig. 5, Part II, 6). The pelvis together
with the lumbo-sacral vertebræ forms a thin, irregular, shell-like
structure extending superiorly from the tail to the thoracic region. The
sacrum is broad posteriorly and together with the ilium forms the pelvic
roof. The ilium and ischium are its lateral walls.

The top surface of the pelvis shows the _fovea ilio-lumbalis dorsalis_,
which is bounded mesially by the crista ilii. Between it and the spina
lumbalis there is a broad furrow, the bottom of which is formed by the
dorsal surface of the lumbar vertebræ. The _sulcus ilio-lumbalis
dorsalis_ is formed by the rims of the ilia, so that a ridge is
observable. The _cavum ilio-lumbale dorsale_ is formed by the iliac rims
on either side. Anteriorly is the _canalis ilio-lumbalis_, which is
formed by the ilium and the lumbar vertebral spines. It is located
longitudinally to the vertebræ. The anterior opening of this canal is
the larger. Posterior to the _acetabulum_ is the _post-acetabular_
ridge.

The under part of the pelvis presents three distinct regions. The cavity
is divided into the _fovea lumbalis_, or anterior part, the _fovea
ischiadica_, or mesial part, and the _fovea pudendalis_, or posterior
part. Posterior to these is the region called the _planum coccygeum_.

The fovea lumbalis contains the anterior lobe of the kidney, and is
circumscribed anteriorly by the last rib-carrying vertebra, and
posteriorly by the transverse process of the last lumbar vertebra.

In the fovea ischiadica which follows, lie the nerve plexus ischiadicus
and the middle lobe of the kidney. Its posterior boundary is the linea
arcuata. The linea arcuata is a line drawn from the acetabulum of the
one side to the acetabulum of the other side.

The fovea pudendalis contains the posterior lobe of the kidney. The
posterior boundary is the anterior border of the first coccygeal
vertebra. It gives passage to the nerve plexus pudendo-hemorrhoidalis.

The ilium, the ischium, and the pubis join to form the cotyloid cavity,
or acetabulum, in which articulates the head of the femur. The floor of
the cavity is perforated by a relatively large round foramen.

=The Ilium.= _Location._—The ilium, together with the lumbo-sacral
vertebræ, forms the roof of the pelvic cavity. It articulates at its
inner border with the lumbo-sacral vertebræ, postero-laterally with the
ischium and at the cotyloid cavity with the pubis.

_Description._—The ilium is remarkable for its development in the long
axis of the vertebral column. It is long and narrow; and mesially, where
it is thickest it forms the upper wall of the acetabulum. Anterior to
the acetabulum it is outwardly concave, and posterior to the acetabulum
it is convex. The ilium fuses with the last dorsal vertebra and with the
lumbo-sacral vertebræ and is excavated on its internal face. This
surface is irregular and lodges the kidneys. This inner margin of the
renal part enters with the square extensions of the posterior excavation
passing into the posterior iliac spine. The external margin is the
extension of the crista transversa and forms the _processus
ischiadicus_. Posteriorward the renal part of the ilium joins the
ischium.

The ilia converge at the summits of the anterior sacral spines forming
the _ilio-lumbar_ spines.

The ilium is joined to the square extensions of the last sacral vertebra
by the _symphysis ilio-sacralis_, to the larger part of the lumbar
vertebræ by the _sutura ilio-lumbalis_, and to the transverse processes
of the last sacral vertebræ by the _symphysis ilio-sacri_.

=The Ischium.= _Location._—The ischium is located in the
postero-inferior part of the pelvis. It joins superiorly with the ilium,
and inferiorly with the pubis.

_Description._—The ischium is smaller than the ilium and is a flattened,
triangular-shaped bone, thickest where it forms the posterior part of
the acetabulum, becoming thinner and broader as it extends backward.
Posteriorly it forms the caudal extension. The inferior border is turned
slightly outward and is fused with the pubis. Between these bones there
is located the large oval _ischiadic foramen_, through which passes the
ischiadic nerve. This bone aids the ilium in the formation of the
obturator foramen through which passes the tendon of the internal
obturator muscle. The lower part of the ischium which separates the
ischiadic foramen from the obturator foramen is called the _ramus
ascendens ossis ischii_.

=The Pubis.= _Location._—The pubis is located along the inferior margin
of the ischium and extends further back than the posterior border of the
ischium.

_Description._—The pubis is a long, slender, rib-like bone. It forms the
lower and front portion of the acetabulum. The ischiadic foramen formed
by the ischium and pubis is single and nearly circular in fowls, double
in pigeons, and in geese and ducks it is elongate.


THE HIND LIMB (Fig. 4, Nos. 35, 47, 48, 49, 50, 51, 52, and 53; Fig. 12)

The pelvic, or hind, limb supports the body. The bones of each leg are
the femur, which constitutes the thigh, the tibia and the fibula, which
represents the leg, and the metatarsus and the phalanges, which form the
foot.

=The Femur= (Fig. 12, _A_ and _B_). _Location._—The femur, or os
femoris, the first bone of the hind extremity, extends obliquely
downward and forward, articulating with the acetabulum above and the
tibia, the fibula, and the patella below.

_Description._—The femur, one of the largest, thickest, and strongest
bones of the body, belongs to the class of cylindrical bones, and
presents for examination a shaft and two extremities.

The superior, or proximal extremity, is provided with a head, caput
femoris; the neck, collum femoris; and the trochanter. The head is
relatively small, and is marked by a depression above for the round
ligament which fills the cavity in the acetabular wall. Its axis is
nearly at right angles with the shaft. A neck joins it to the body at
the proximal end. External to the head of the femur is the _trochanter_.
The trochanter presents an outer convexity over which the tendon of the
gluteus maximus extends to become inserted below. The _trochanteric
ridge_, which is opposite the articular head, presents an outer
flattened surface which possesses impressions for muscular attachments.
The _trochanteric fossa_, or fossa trochanterica, is shallow.

The _shaft_, or _corpus femoris_, is shorter than the tibia, is in
general cylindrical, bent forward, and the lower half is flattened and
expanded transversely. A nutrient foramen is located in the median
portion of the shaft. The shaft shows muscular linear ridges.

The distal extremity is large in both directions and comprises the
_trochlea_ in front and two _condyles_ behind, one internal and one
external. The condyles are separated by the _intercondyloid fossa_, or
_fossa intercondyloidea_, which is marked with pits for the attachment
of ligaments; and above this is the _epitrochlear fossa_.

[Illustration:

  FIG. 12.—Bones of the hind extremity.

  _A._ Posterior view of femur.

  _B._ Anterior view. 1, Shaft. 2, Proximal extremity. 3, Distal
    extremity. 4, Articular head. 5, Trochanter major. 6, Shallow
    trochanteric fossa. 7, Convexity over which the tendon of the
    gluteus maximus glides. 8, External condyle. 9, Internal condyle.
    10, Nutrient foramen. 11, Intercondyloid fossa. 12, Muscular linear
    ridges. 13, Epitrochlear fossa.

  _C._ Internal view of tibia.

  _D._ External view. 1, Shaft. 2, Articular head. 3, Distal end. 4, The
    rotular process. 5, The fibular ridge. 6, External condyle. 7,
    Internal condyle. 8, Intercondyloid space. 9, Nutrient foramen.

  _E._ Fibula, lateral view. 1, Articular head. 2, Its attenuated
    portion.

  _F._ Posterior view of metatarsus. 1, Trochlea for inner or second
    digit. 2, Trochlea for middle or third toe. 3, Trochlea for outer
    digit. 4, Bony core for spur. 5, Bony canal for tendons. 6, Groove
    for tendons. 7, Fossa intercondyloidea.
]

The _inner condyle_ begins anteriorly as a ridge, and expands into a
convexity which attains its greatest breadth posteriorly where it
becomes more flattened. The inner side of the inner condyle is flattened
and is provided with a tuberosity at its mid-part and a second just
above the posterior part of the condyle.

The _outer condyle_ is formed in the same manner as the inner condyle.
It is indented at its broad, lower end by an _angular groove_, which,
winding divides the posterior part of the condyle into two convexities.
The more external convex ridge and the groove dividing it from the outer
condyle are adapted to the head of the fibula. There is in this part a
_fibular ridge_ and above this ridge a tuberosity.

=The Tibia.= _Location._—The tibia (Fig. 12, _D_ and _C_) extends
obliquely downward and backward from the knee-joint to the hock. It
articulates above with the femur and, by its procnemial process with the
patella, below with the metatarsus, and laterally with the fibula.

_Description._—The tibia is the longest bone in the posterior limb, and
possesses a shaft and two extremities. It is largest at the proximal end
and presents three faces.

The proximal extremity presents a semi-oval articular surface, not quite
at right angles with the shaft, which articulates with the condyles of
the femur. The margin is raised toward the anterior of the bone. The
_head of the tibia_, or _caput tibiæ_, extends into a rotular process
which extends transversely, and is truncate. From the anterior of this
process there descends two vertical ridges; one near the angle of the
rotular process, the _procnemial ridge_; the other from the outer
fibular angle, the _ectocnemial ridge_. On the outer side of the
intercondylar tuberosity there is a surface for the ligamentous union
with the head of the fibula; and a short distance below this there is a
vertical ridge for the close attachment, almost a fusion, with the
fibula, called the _fibular ridge_.

The _shaft_, or _corpus tibiæ_ is straight and the upper two-thirds
subtrihedral; the lower third oval. A _nutrient foramen_ occurs near the
upper postero-internal portion of the middle third of the bone.

The distal extremity is much smaller than the proximal one; it is
quadrangular in form. The expanded inferior end of the tibia forms two
articular condyles above which posteriorly there is the _epicondyloid
fossa_. The inner condyle, the larger, has a groove near the lower end
of the anterior part of the shaft, which deepens toward the
intercondyloid space. This _intercondyloid fossa_ in young birds is
covered by a strong ligament, which in older birds, becomes ossified. On
the lateral side of each condyle, there is a depression for the
attachment of ligaments.

=The Patella.= _Location._—The patella, or knee-cap, thin and wide,
articulates with the procnemial process of the tibia, and with the deep
trochlea of the distal end of the femur.

_Description._—The patella is irregular in shape with three faces and
three borders. The posterior surface is articular. The other two
surfaces are rough for tendinous attachment. The patellar ligaments in
old birds may become ossified.

In order to turn the foot in and out, the tibia not only turns around
the inner condyle of the femur, but also around the patella, so that the
posterior surface turns outward and thus turns outward the metatarsus
and all the toes.

=The Fibula.= _Location._—The fibula lies at the outer border of the
tibia. It articulates superiorly with the outer condyle of the femur,
and laterally with the tibia.

_Description._—The fibula is rudimentary; it is largest superiorly and
tapers to a slender point. The head is compressed laterally, and
furnishes an upper and an inner articular surface.

=The Tarsus.=—There exist, during fetal development of the chick, two
rows of tarsal bones which later become fused. The upper row fuses with
the tibia and the lower with the metatarsus. Therefore, in the adult,
there is no tarsus.

=The Metatarsus.= _Location._—The metatarsal bone extends downward and
forward. In birds it consists of one bone, which articulates superiorly
with the inferior extremity of the tibia. On the distal end it has a
threefold trochlear arrangement which articulates with the three
principal digits.

_Description._—The proximal extremity posteriorly has a process which
may be considered as a consolidation of originally separate metatarsal
bones. The process at the supero-posterior part of the metatarsus is
called the _hypotarsus_ of the _tarso-metatarsus_, through which extends
a canal called the _hypotarsal canal_, and which gives passage to flexor
tendons.

The proximal end of the metatarsus is ossified from one center of
ossification forming an epiphysis which caps the ends of the three
original metatarsal bones that coalesce, first with one another, then
with the epiphysis, thus forming a single compound bone. Above and just
to the inside of the metatarsus there may occur a small bone which is
imbedded in ligaments and articulates with the inner proximal surface of
the metatarsus. This has been called by Gadow a _sesamoid bone_.

The shaft shows _tendonal grooves_ which are best marked on the
posterior surface. The shaft is rounded at the sides and flattened on
the anterior and posterior surfaces. At the juncture of the middle and
inferior thirds of the metatarsus there is a conical process turned
slightly backward, which serves as a base for the _spur_. The spur is a
horny structure.

At the distal extremity occurs the threefold trochlear arrangement
mentioned above, which incloses the fossa intercondyloidea. The inner
trochlea is the broadest, and the outer the narrowest. The inner
trochlea articulates with the proximal end of the second, the middle
with the third, and the outer with the fourth toe.

=The Phalanges.= _Location._—Most domestic fowls are provided with four
digits, or toes; the Houdan and Dorking are provided with five. In fowls
with four toes the three principal toes, the second, the third, and the
fourth, are directed forward, and the first, or hallux, is directed
backward.

_Description._—The last phalanx of each toe, called the ungual phalanx,
is slightly curved downward, is pointed anteriorly, like the claw of the
cat or dog, and is covered with a horny sheath. The articular ends of
the joints of the phalanges are enlarged. The base of the basal phalanx
has two enlargements, the superior-inferior tubercles, or tuberculum
superius et inferius, between which is located the fossa articularis
transversa. Laterally the head has two condyles, condyli laterales,
which are divided by the sulcus longitudinalis. The bodies of the
phalanges vary in form; they are superiorly rounded, but inferiorly
rounded, flat, or even somewhat concave. The distal extremity has an
articular trochlea.

The _first toe_, or digit, called the _great toe_, or _hallux_, is
composed of three phalanges, or segments. The first segment, or basal
phalanx is considered a rudimentary metacarpal bone; it is attached by a
fibrous cartilaginous tissue to the inner posterior surface of the
inferior extremity of the metacarpal bone just below the spur.

The _second toe_, likewise composed of three phalanges, is directed
forward. It articulates with the inner trochlea located on the inferior
metacarpal bone.

The _third toe_, made up of four phalanges, is the middle of the three
forward toes. It articulates with the middle trochlea of the inferior
extremity of the metacarpal bone.

The _fourth toe_, is composed of five phalanges; it is, however, of
approximately the same length as the third, the segments being shorter.
The fourth or outer toe articulates with the outer trochlea of the
distal extremity of the metacarpal bone.




                               ARTHROLOGY


=Kinds of Joints.=—Joints may be movable, immovable, or mixed. In
_movable_, or _true joints_ the articular surface of each bone is
covered by cartilage. The bones are held together by ligaments, the
capsular one often surrounding the joint and enclosing the synovial
membrane. In some joints there is a pad of fibrous cartilage interposed
between the two articular cartilages. Such a pad, called a _meniscus_,
adds to the elasticity and the free movement of the joint. Movable
joints form the most numerous class; they are for the most part found in
the limbs.

In an _immovable joint_ there is only a thin layer of fibrous or
cartilaginous material interposed between the bones. The fibrous layer
of the periosteum of both bones unite to cover the connecting material
and becomes attached to the same, thus serving as a ligament. If the
connecting material is fibrous, the joint is called a _suture_; if
cartilaginous, a _synchondrosis_. These joints are found in the skull
and in the pelvis.

The term _mixed_ is used with reference, not to the motion in joints,
but to their structure, which partakes of the nature of both the movable
and immovable. The bones are firmly joined by a strong interposed pad of
fibrous cartilage to which also is adherent the ligaments of the joint.
There are no capsular ligaments; the cartilaginous pad or disc is softer
toward its center, where occasionally there may be one, or even two,
narrow cavities. Authorities differ as to whether such cavities are
lined by synovial membrane or not. Since there are really no frictional
surfaces in such a joint, motion depends upon the flexibility of the
disc. The joints between the vertebral centra afford the best
illustration of the mixed class.

=Movement of Joints.=—The movements admissible in joints may be divided
into four kinds: gliding, angular movement, circumduction, and rotation.
These movements are often, however, more or less combined in the various
joints. It is seldom that there occurs only one kind of motion in any
particular joint.

_Gliding movement_ is the most simple kind of motion that can take place
in a joint, one surface gliding or moving over another without any
angular or rotary movement.

_Angular movement_ occurs only between the long bones. By it the angle
between the two bones is increased or diminished. It may take place in
four directions: forward and backward, consisting of flexion and
extension; or inward and outward from the medial line of the body,
consisting of adduction and abduction. Abduction of a limb is movement
away from the medial line of the body. Adduction of a limb is movement
toward the medial line of the body.

_Circumduction_ is that limited degree of motion which takes place
between the head of a bone and its articular cavity, whilst the
extremity and sides of the limb are made to circumscribe a conical
space, the base of which corresponds with the inferior extremity of the
limb, the apex with the articular cavity; this kind of motion is best
seen in the shoulder- and hip-joint.

_Rotation_ is the movement of a bone upon an axis, which is the axis of
the pivot on which the bone turns, as in the articulation between the
atlas and axis, when the odontoid process serves as a pivot around which
the atlas turns; or else is the axis of a pivotlike process which turns
within a ring, as in the rotation of the radius upon the humerus.

_Pronation_ is a form of rotation in which the inferior extremity of the
radius passes before the ulna, and thus causes the hand to execute a
kind of rotation from without inward.

_Supination_ is a form of rotation in which the movement of the forearm
and hand are carried outward so that the anterior surface of the latter
becomes superior.

=The Ligamentous Structure.=—Ligaments are dense, fibrous, connecting
structures. They are made up principally of white fibrous tissue and
exist in all true joints.

There are four kinds of ligaments associated with true joints:

The first kind, the _capsular ligament_ which encloses all true joints,
is thin and consists of interlaced fibers attached to the bone at the
edges of the articular cartilages. It either partly or wholly surrounds
the joint, enclosing and protecting a synovial apparatus, which, by
secreting a liquid resembling serum, lubricates the joint to prevent
friction.

The second kind, the binding or _lateral ligaments_, consist of
flattened or rounded cords or bands of fibrous tissue. Such a ligament
extends from one bone to the other, and firmly attached to their
roughened surfaces, holds the bones in place and at the same time allows
the required amount of motion.

The third kind, located between the joints, is called _interosseous
ligament_.

The fourth kind, called the _annular ligament_ binds down and protects
the tendons.

=Ligaments of the Ear[2].=—The concha of the ear is provided with a
superior and an inferior ligament.

Footnote 2:

  The classification of Gadow is used.

=Ligaments of the Jaw.=—The articulations of the lower jaw are complex.
The freely movable articulation is between the inferior maxilla and the
quadrate. Less freely movable articulations are formed by the quadrate
with the temporal, the zygomatic and the pterygoid. A lateral ligament
of the jaw, the _articulo-jugale_ extends from the posterior border of
the inner wing of the os articulare of the inferior maxilla (Fig. 8, No.
10, and Fig. 19, No. 15) to the outer border of the os quadrato
jugulare.

A _lateral temporo-maxillary ligament_ extends from the outer surface of
the temporal bone to the outer border of the os articulare of the
inferior maxilla (Fig. 8, No. 11, and Fig. 19, No. 14).

=Ligaments of the Vertebræ.=—In each space between the bodies of the
vertebræ there is a _meniscus intervertebralis_. This meniscus is
analogous to the annulus fibrosus of mammals (Gadow), which, is possibly
formed as a protrusion of the anterior surface of the vertebral body.
The meniscus or disc may develop into a ring-shaped structure, the true
meniscus, or it may develop to different degrees as an extension of the
vertebral body surface, and become, as in the dorsal and lumbar regions,
fused with the vertebral segments, in which case it is called the
annulus fibrosus.

The vertebral disc which is connected with the atlas and which is fused
with that bone, represents the first meniscus, which is called the
_ligamentum transversum atlantis_. This, as well as other ligaments of
the spinal column, may become ossified.

The ligament which is located between those vertebral bodies which face
each other and is inside the joint cavity, is called the _ligamentum
suspensorium corporum vertebralium_. It passes through the central
opening of the meniscus and lies exactly in the long axis of the body of
the vertebra.

The first ligament of the neck is the _ligamentum suspensorium dentis
epistrophei_. The _ligamentum capsulare atlantico-occipitale_ and the
_ligamentum capsulare atlantico-epistrophicum odontoideum_ are two parts
of the joint capsule of the vertebral body. Other ligaments of this part
are the _membranæ obturatoriæ intervertebrales posteriores_, which are
located between the semicircular rims of the neck vertebræ.

The _ligamentum transversum atlantis_ surrounds the occipital condyle.

The _ligamentum nuchæ_ is a thin, membranous, ribbon-like structure
which lies between the muscles of the right and those of the left side
of the middle, and the lower part on the posterior of the neck, and ends
in attachments to the superior spines of the cervical vertebræ.

The _ligamentum elasticum interspinale profundum_ and the _ligamentum
elasticum interspinale superficiale_ and the three last named are the
ligaments which keep the neck of the fowl in the s-shape, without the
action of the muscles.

The _ligamentum capsulare obliquum_ connects the facets of the oblique
processes.

=Ligaments of the Ribs.=—The thick inferior end of the sternal portion
of the true rib has two small articular heads, which articulate with two
depressions in the articular surface of the sternum. This articulation
is held firm by a _capsular ligament_.

The upper end of the sternal rib forms an almost perfect right angle
with the inferior end of the dorsal rib with which it is connected by a
joint provided with a synovial apparatus and a capsular ligament. This
arrangement allows free movement outward and inward and is the main
joint in respiration.

The upper end of the dorsal portion of the rib articulates with the
dorsal vertebra. The joint formed by the articular head with the body of
the vertebra is provided with a capsular ligament. The tubercle of the
rib articulates with the facet on the transverse process of the dorsal
vertebra, and is provided with a transverse ligament, called the
_ligamentum transversum externum_. It is also provided with a capsular
ligament.

The _ligamentum triangulare_ connects each processus uncinatus with the
succeeding rib. This ligament is in the form of a membranous sheet, or
aponeurosis.

=Ligaments of the Sternum= (Fig. 13).—The external and the internal
notches of the sternum are bridged over with a thin membrane which gives
an extensive surface for muscular attachments. The sternal muscles
overlie this portion.

[Illustration:

  FIG. 13.—Muscles of the fore extremity. Inside view. 1, Lateral
    external process of sternum. 2, Lateral internal process of same. 3,
    Ligament of the external notch. 4, Ligament of the internal notch.
    5, Pectoralis major. 5_a_, Its fan-shaped expansion at
    shoulder-joint laid back. 6, Pectoralis tertius. 7, The coracoid. 8,
    Biceps. 8_a_, Its long head. 8_b_, Its short head. 9, Pectoralis
    secundus. 10, Rectus abdominis. 11, Teres et infraspinatus. 12,
    Deltoid. 13, Capsular ligament. 14, Teres minor. 15,
    Coraco-brachialis. 16, Serratus magnus anticus. 17, Extensor
    metacarpi radialis longior. 18, Pronator brevis. 19, Flexor carpi
    ulnaris. 20, Flexor carpi ulnaris brevior. 21, Flexor digitorum
    profundus. 22, Extensor indicis longus. 23, Extensor ossis metacarpi
    pollicis. 24, Humerus. 25, Shoulder. 26, Elbow. 27, Carpus. 28,
    Section through vertebra. 29, Keel of sternum. 28_a_, Flexor brevis
    pollicis. 29_a_, Extensor proprius pollicis. 30, Flexor minimi
    digiti brevis. 31, Interosseous palmaris. 32, Interosseous palmaris.
]

The sternum is connected by a fibrous mass with the inferior portion of
the clavicle, or hypocledium (Fig. 57), the _claviculosternal ligament_.

The inferior narrow elongated end of the coracoid forms with the sternum
a true articulation, which is provided with a capsular ligament, the
_ligamentum capsulare_. Capsular ligaments occur at the articulations
between the sternum and ribs.

=Ligaments of the Shoulder-joint= (Fig. 13).—The shoulder-joint is made
up of the scapula, the humerus, and the coracoid. The ends of these
three bones form the _foramen triosseum_ (Fig. 15, No. _A_, 7) through
which passes the tendon of the elevator muscle of the wing.

The furcula, independent of the shoulder-joint or girdle, is attached to
the supero-internal part of the proximal end of the coracoid by fibrous
connective tissue; it is also connected to the other bones of the
shoulder-joint by the _ligamentum coraco-furculare_ and the _ligamentum
furculo-scapulare_.

The _ligamentum coraco-scapulare_ extends from the tuberosity of the
furcula to the coracoid and to the processus furcularis of the scapula.

The _ligamentum coracoido-scapulare externum_ extends between the
external tuberosity of the coracoid, the tuberosity of the scapula, and
the humerus.

The _ligamentum coracoideo-scapulare inferius_ extends from the coracoid
to the inner tubercle of the scapula.

Another long, broad ligament belongs to the episternal apparatus.

The shoulder-joint is provided with a wide, loose, _capsular ligament_
(Fig. 13, No. 13). Attached to the humerus are four other ligaments, of
which three pass from the anterior end of the coracoid and the fourth
from the scapula. The latter are as follows: first, the _supero-anterior
ligamentum humero-coracoideum_, which extends from the small tubercle of
the humerus to the coracoid bone; second, the _antero-inferior
ligamentum humero-coracoideum_, which extends from the humerus to the
coracoid; third, the _ligamentum coraco-humerale_, which extends from
the coracoid to the large tubercle of the humerus; fourth, the
_ligamentum humero-scapulare_ which extends between the processus
humeralis of the scapula and the head of the humerus.

=Ligaments of the Elbow-joint= (Fig. 14).—The elbow-joint is made up of
the ulna, radius and the humerus. The ligaments of the elbow-joint are
as follows: the _ligamentum capsulare cubiti_, or capsular ligament,
which extends from the processus cubitalis of the humerus to the
processus olecranalis coracoideus of the ulna and to the tuberositas
radii of the radius (Fig. 15, No 5).

The _ligamentum laterale cubiti externum_ connects the outer humeral
distal extremity with the head of the radius (Fig. 15, No. 2).

The _ligamentum laterale cubiti internum_ lies between the inner distal
extremity of the humerus and the tuberculum internum of the ulna (Fig.
14, No. 9).

The _ligamentum annulare radii_ originates on the olecranon, surrounds
the head of the radius, and is attached to the tuberculum internum of
the ulna (Fig. 15, No. 3).

The _ligamentum cubiti teres_ extends from the head of the radius to the
upper end of the ulna (Fig. 15, No. 4).

[Illustration:

  FIG. 14.—Muscles and ligaments of the arm and forearm of a hen.

  _A._ External view. 1, Expansor secundarium. 2, Tensor patagii longus.
    3, Tensor patagii brevis. 5, Brachialis anticus. 6, Pronator longus.
    7, Supinator brevis. 8, Extensor indicis brevis. 10,
    Scapulo-humeralis.

  _B._ Internal view. 9, Ligamentum laterale cubiti internum.
]

The _ligamentum transversum_ spreads out between the head of the ulna
and the radius, thus uniting the two bones, and limiting supination
(Fig. 15, No. 1).

=Ligaments of the Carpal Joint.=—The carpal joint is made up of the
ulna, radius, the two carpal bones and the metacarpus.

There are two strong _ligamenta obliqua carpi ulnaris_ which extend from
the processus styloideus of the ulna to the tuberculum posterius carpi
ulnaris of the os carpi ulnaris.

The _ligamentum posticum ulnare carpi ulnaris_ extends from the
processus styloideus of the ulna to the os carpi ulnaris.

[Illustration:

  FIG. 15.—Ligaments of the arm and forearm of a hen.

  _A._ The scapulo-coraco-humeral articulation. 1, Proximal end of the
    humerus. 2, Articular head of humerus. 3, The coracoid. 4, Proximal
    end of the clavicle. 5, Tendon of pectoralis tertius. 6, Tendon of
    pectoralis secundus. 7, Opening or foramen triossium through which
    the tendon of the elevator of the wing passes. (Pectoralis
    secundus.) 8, Broken end of scapula.

  _B._ 1, Ligamentum transversum. 2, Ligamentum laterale cubiti
    externum. 3, Ligamentum annulare radii. 4, Ligamentum cubiti teres.
    5, A portion of the ligamentum capsulare cubiti. 6, Distal extremity
    of humerus. 7, Ulna. 8, Radius.

  _C._ Muscles of the outside surface of the arm. 1, Tensor patagii
    longus. 2, Extensor digitorum communis. 3, Tensor patagii brevis. 4,
    Anconeus. 5, Flexor carpi ulnaris. 6, Biceps. 7, Triceps. 8.
    Deltoid. 9, Brachialis anticus. 10, Flexor metacarpi radialis. 11,
    Extensor ossis metacarpi pollicis. 12, Extensor metacarpi radialis
    longior. 13, Extensor indicis longus.
]

The _ligamentum ulnare carpi radialis_ is a short ribbon-like ligament
which passes over the above-mentioned ligaments and is attached to the
inner surface of the os carpus radialis.

The _ligamentum ulnare carpi radialis internum_ is a strong ligament
which originates on the inner part of the elbow. It extends to the upper
rim of the base of the main digit.

The _ligamentum radiale carpi radialis externum_ originates on the
outside of the head of the middle digit and inserts to the superior
tuberculum carpi radialis of the radius.

The _ligamentum carpi radialis internum_, a short ligament, extends from
the inside of the head of the main digit to the inner rim of the carpi
radialis.

The _ligamentum carpi interosseum_ is located between the carpal bones.

The _ligamentum ulnare metacarpi internum_ is spread out between the
processus styloideus of the ulna and the tuberositas muscularis on the
upper side of the middle finger base at a point where the second and the
third metacarpi separate.

The _ligamentum ulnare metacarpi externum_ extends from the tubercle of
the distal extremity of the ulna, on the dorsal side, to the tubercle on
the base of the metacarpus.

_Ligamentum radiale metacarpi_ extends from the head of the inner digit
to a point near the tuberculum muscularis of the radius.

The _ligamentum transversum ossis carpi radialis et metacarpi_ is
located between the inferior tuberculum ossis carpi radialis and the
first metacarpal bone.

There is another ligament between the tuberculum superiorus carpi
radialis and the first metacarpal bone.

The _ligamentum ossis carpi radialis internum et metacarpi_ extends from
the inner surface of the carpus radialis to the tuberositas muscularis
of the radius.

The _ligamentum ossis carpi ulnaris externum et metacarpi_ extends from
the ulnar carpal bone to the tuberculum of the metacarpal bone.

The _ligamentum ossis carpi ulnaris internum et metacarpi_ extends from
the processus uncinatus of the ulnar carpal bone to the tuberositas
muscularis of the metacarpal bone.

=Ligaments of the Finger.=—The _ligamentum pollicare_ connects the thumb
with the first metacarpal bone.

The _ligamentum anterius ossis metacarpi et primæ phalangis digiti
secundi_ extends from the tuberculum articulare metacarpi, of the
proximal end of the metacarpus, to the tuberculum articulare of the
first phalanx of the second or large finger. Similarly attached, are
also an internal and a posterior ligament, or _ligamentum internum_ and
_ligamentum posterius_.

The three phalanges are all provided with capsular ligaments, or
ligamenta capsularia, which bind together the several phalanges.

The small or third finger is connected to the metacarpus by a capsular
ligament, the _ligamentum capsulare_, and by an interosseous ligament,
or _ligamentum interosseum digitorum_, to the first phalanx of the
second finger.

=Ligaments of the Pelvis.=—The obturator foramen, formed by the ilium
and the ischium, is covered by a broad membranous ligament (Fig. 4, No.
29).

The oblong foramen, or foramen oblongum, and the foramen ischiadicum,
formed by the ischium and the pubis are covered by broad membranous
ligaments (Fig. 4, Nos. 29 and 60).

_Poupart’s ligament_ or _ligamentum Poupartii_, quite small in fowls,
extends from the anterior lower rim of the ilium to the pelvic cavity,
and is inserted at the bottom of the acetabulum.

Another broad ligament originates from the posterior rim of the ischium
and is attached to the square surface of the first coccygeal vertebra.

The _ilio-pubic ligament_ extends from the pubic spine to the last
rudimentary rib.

=Ligaments of the Hip-joint= (Fig. 25, _F_).—The hip-joint is made up of
the ilium, ischium, pubis and femur and is a deep ball-and-socket joint.
The cavity or acetabulum is called a cotyloid cavity.

The hip-joint is provided with three ligaments.

The _ligamentum capsulare femoris_ is attached around the rim of the
cotyloid cavity and around the rim of the articular head of the femur
(Fig. 25, No. _F_, 4).

The _ligamentum teres_, or _round ligament_, is a very short ligament
which closes the hole at the floor of the cotyloid cavity, at which
point it is attached. It is also attached to the head of the femur.

The _ligamentum ilio-sacrale_ strengthens the hip-joint capsule. It
passes from the lower anterior rim of the os ilii, extending over the
capsule to the neck of the femur to which it is attached.

=The Ligaments of the Knee-joint= (Figs. 16 and 17).—The knee-joint is
made up of the femur, patella, tibia and fibula, and is provided with
the following ligaments:

The _ligamentum extero-laterale genu_ is a strong ligament extending
from the condylus externus femoris, or external femoral condyle to the
outer surface of the head of the fibula, or capitulum fibulæ. From this
head there passes inward, a strong ligament to a point between the femur
and fibula (Fig. 25, No. _D_, 4).

[Illustration:

  FIG. 16.—Ligaments and muscles of the hind extremity.

  _A._ A transverse section through the tibial or tarsal cartilage,
    front view. 1, Gastrocnemius tendon. 2, Flexor perforatus annularis
    primus pedis. 3, Flexor perforans digitorum profundus. 4, Flexor
    perforatus indicis secundi pedis. 5, Extensor longus hallucis. 6,
    The articular surface. 7, Ligamentum capsulare ossis tarsi. 8,
    Flexor perforatus medius secundus pedis. 9, Flexor perforatus
    indicis secundus pedis. 10, Tendons of the extensor muscles.

  _B._ Knee-joint. Inside view of femoro-tibial articulation. 1,
    Anterior ligamentum cruciatum. 2, Internal ligamentum laterale genu.
    3, Anterior patellar ligament. 4, Patella. 5, Distal end of femur.
    6, Proximal end of tibia. 7, Location of meniscus or pad of
    fibrocartilage.

  _C._ Anterior view of tibio-tarsal articulation. 1, Distal end of
    tibia. 2, Its articular surface. 3, Ligamentum anticum. 4, Proximal
    end of metacarpus. 6, Pad of fibrocartilage.

  _D._ The dorsal surface of the coccyx. 1, The bilobate oil gland. 2,
    Its duct. 3, Levator coccygis.

  _E._ Inside view of pelvis and thigh. 1, Obturator internus. 2,
    Ambiens. 3, Vastus internus. 4, Internal ligamentum laterale genu.
    5, Tibialis anticus. 6, Loop through which the tibialis anticus
    passes. 7, Adductors of the thigh. 8, Loop for the extensor tendon.
]

The _ligamentum intero-laterale genu_ extends from the outer surface of
the internal condyle of the tibia, or condylus internus tibiæ. It gives
off a thin ligamentous slip which enters the joint and is attached to
the inner half-moon shaped pad of fibrous cartilage, or meniscus, which
it draws backward by the flexion of the knee (Fig. 16, No. _B_, 2).

The _ligamentum popliteum_ arises from the fossa poplitea of the distal
extremity of the femur and extends downward to the posterior rim of the
head of the tibia.

The _anterior ligamentum cruciatum genu_ originates from the fossa
poplitea and extends outward antero-laterally to the rim of the head of
the tibia (Fig. 25, No. 6).

The _posterior ligamentum cruciatum genu_ is a short, strong ligament
which originates from the cavity of the internal condyle of the femur,
or condylus internus femoris, and inserts into the internal glenoid
cavity of the tibia (Fig. 25, No. 1) or cavitas glenoidalis interna.

The meniscus of the femoro-tibial articulation is divided into four
parts, as follows: first, the _internal adhesio cornu antici
cartilaginis lunatæ_; second, the _posterior adhesio cornu antici
cartilaginis lunatæ_; third, the _external cornu cartilaginis lunatæ_;
fourth, the _anterior cornu antici cartilaginis lunatæ_. The latter
originates between the condyles and passes around the ligamentum
cruciatum genu posticum (Fig. 16, No. _B_, 7).

The inner semi-lunar fibrous cartilage is well developed and is joined
by two ligaments between the femoral and the tibial surfaces (Fig. 25,
No. 1).

The external semi-lunar cartilage lies in a cavity between the external
femoral condyle and the head of the fibula (Fig. 25, No. 2).

The fibrous cartilages are bound posteriorly by a ligament, and by a
second ligament to the head of the fibula, or capitulum fibulæ. Both
pads of fibrous cartilage are connected by a transverse ligament called
the _ligamentum transversale commune_ (Fig. 25, No. 5).

The patella is provided with several ligaments, as follows:

The _anterior patellar ligament_, broad, strong, and irregular in
thickness, extends from the inferior margin of the patella to the rim of
the second tibial crest (Fig. 16, No. _B_, 3).

The _ligamentum capsulare capituli fibulæ_ is spread out between the
head of the fibula, or capitulum fibulæ, and the superficies glenoidalis
peronea tibiæ.

[Illustration:

  FIG. 17.—Muscles and tendons of the head and posterior extremity.

  _A._ Section of neck with superficial muscles removed. 1,
    Obliquo-transversales. 2, Interspinales. 3, Intertransversales. 4,
    Interarticulares.

  _B._ Head showing muscles. 1, Beak. 2, Nostril. 3, Tongue. 4,
    Sublingual salivary gland. 5, Pterygoideus. 6, Stylo-hyoideus. 7,
    Temporal. 8, Flexor capitis inferior. 9, Rectus capitis lateralis.
    10, Rectus capitis posticus major. 11, Trachelo-mastoideus. 12, Eye.
    13, Mylo-hyoideus. 14, Genio-hyoideus. 15, Biventer maxilla. 16,
    Digastricus. 17, Rectus capitis anterior minor.

  _C._ Foot of hen showing tendons. 1, Flexor perforans digitorum
    profundus. 2, Flexor perforatus medius primus pedis. 3, Sheath at
    joint through which tendon passes. 4, Flexor perforatus indicis
    primus pedis. 5, Flexor perforatus medius secundus pedis. 6, Flexor
    perforatus annularis primus pedis. 7, Flexor longus hallucis.

  _D._ Outside view of leg of hen. 1, Biceps flexor cruris. 2,
    Semitendinosus. 3, Loop through which biceps flexor cruris passes.
    4, Tibialis anticus. 5, Flexor perforatus indicis secundus pedis. 6,
    Flexor perforatus medius primus pedis. 7, Gastrocnemius. 8, Flexor
    perforatus annularis primus pedis. 9, Flexor perforatus medius
    secundus pedis. 10, Extensor longus hallucis.
]

The _ligamentum tibio-fibulare_ extends from the head of the fibula, or
capitulum fibulæ, to the inner surface of the external crest, or crista
externa tibiæ, of the tibia (Fig. 25, No. 3).

The _ligamentum interosseum_ is a delicate ligament located between the
tibia and fibula (Fig. 25, No. 4) which very early becomes ossified.

=Ligaments of the Tibio-metatarsal Joint= (Fig. 16).—The tibio-tarsal
joint is made up of the tibia and metatarsus.

The _ligamentum capsulare ossis tibio-metatarsi_ connects the tibia and
the metatarsus and surrounds the joint (Fig. 16, Nos. _A_, 7 and _C_,
7).

The _ligamentum externum_, a long strong ligament, originates on the
upper and outer surface of the external condyle, or condylus externus of
the tibia and is attached to the upper rim of the os metatarsi (Fig. 23,
No. 15).

The _ligamentum anticum_ is spread out between the fossa
intercondyloidea of the tibia and the tuberculum ossis metatarsi of the
proximal end of the metatarsus (Fig. 16, No. _C_, 3). Just posterior to
this ligament, there is an interosseous ligament, the _ligamentum
interosseum_.

A semi-lunar pad of fibrous cartilage, the _cartilago semi-lunaris_ is
located between the outer distal extremity of the tibia and upper
articular surface of the metatarsus (Fig. 16, No. _C_, 6). Its concave
portion is directed anteriorly and receives an insertion from the
ligamentum externum, or external ligament.

The tendon Achillis (Fig. 16, No. _A_, 1) may become ossified.

=Ligaments of the Toes= (Fig. 16).—In addition to the capsular
ligaments, which all true joints have, we find the following in
connection with the toes:

The _ligamentum superius_ and the _ligamentum inferius_ connect the
second toe with the great toe, or hallux.

The _ligamentum laterale externum_ and the _ligamentum laterale
internum_ unite the bases of the second, third and fourth toes to the
lateral faces of the trochleas of the inferior extremity of the
metatarsus.

The bases of the toes are held together by the _ligamenta transversa_.
All the rest of the toes are held together by the _ligamenta capsularia
digitorum pedis_ and by two lateral ligaments, namely: the _ligamentum
laterale externum_ and the _ligamentum laterale internum_.




                                MYOLOGY


=Kinds and Structure of Muscles.=—Muscles are highly specialized
structures which have the property of contractility when stimulated, and
thus produce motion. Muscular tissue is sometimes called flesh. Two
kinds of muscles are recognized; muscles of locomotion and visceral
muscles.

The muscles of locomotion may be in masses of different shape attached
to the skin, the _dermal_, or to the skin and skeletal structure, the
_dermo-osseous_, or from one bone to another, the _skeletal_. The
visceral muscles form sheets and make up a portion of the wall of many
of the hollow organs, such as the intestines, the stomach, the gizzard,
the esophagus, and the blood-vessels. A special type of muscle forms the
heart.

When classified with reference to structure, muscular tissue is divided
into three types, as follows: voluntary-striated, involuntary, and
involuntary-striated. The microscopic examination of each of these types
of muscle shows it to be made up of fibers, these fibers to be made up
of muscle cells, the muscle cell to be inclosed in a delicate tubular
sheath, or membrane, called the _sarcolemma_. This membrane, tough and
elastic, isolates each fiber. The bundles of fibers, called _fasciculi_,
are surrounded by a fibrous sheath, which is called the _perimysium
internum_; and the entire muscle has likewise an investing sheath of
connective tissue, called the _perimysium externum_. The muscular cells
show a longitudinal striation marking the fibrillæ, and they also show a
cross striation. Nuclei are found just beneath the covering, or
sarcolemma, in the striated muscle cell (Fig. 77, No. 2). In the
involuntary and in the involuntary-striated muscle cell, the nuclei are
centrally located.

The _voluntary-striated muscles_ consist of cylindrical fibers and with
a few exceptions, are under the control of the will. A muscle of this
type, the regular skeletal form, usually has at each extremity a fibrous
structure, called a tendon, by means of which it is attached to the
bones. The intermediate fleshy portion of the muscle, in case of
considerable bulk, is called the belly of the muscle.

The _involuntary_, _non-striated_, or _smooth muscle_, cells are
spindle-shaped, long, and pale in color (Fig. 77, No. 1). The cells lie
end to end forming fibers. These fibers do not terminate in tendons, but
are arranged in sheets and aid in forming the walls of the digestive
tract, to which they give the power of contraction and expansion.

_Involuntary-striated_, or _heart muscle_ (Fig. 77, No. 4), occupies an
intermediate position between the two muscles just described. It is
composed of cells which branch, are somewhat rectangular. They possess
both longitudinal and transverse striation. Among the fibers is found a
small amount of connective tissue, as in the former types of muscle,
which gives support to the blood-vessels and nerves.

=Fascia.=—The term fascia is applied to membranous expansions, differing
materially in strength, texture, and relations. Fascia is composed of
loosely arranged white fibrous connective tissue. At least two layers
may usually be distinguished, the superficial fascia and the deep
fascia.

Below the skin is the _superficial fascia_, which forms a continuous
covering over the whole body and serves to attach the skin to the
underlying structure.

The _deep fascia_ more densely constructed, may be attached to the
skeleton, ligaments, and tendons.

When the fascia spreads out, becomes denser, and acts as a continuation
of a muscle, it is called an aponeurosis.

=The Muscular Nomenclature.=—In the fowl there are 162 muscles, single
or in pairs. These muscles are named from their location, as the
lingualis; others from their attachments, as the dermo-temporalis; some
from their form, as the rhomboideus; others from their use, as the
flexor or extensor; and still others from their direction, as the
transversus.


                           THE DERMAL MUSCLES

Birds are provided with a system of delicate muscles divided into
numerous fasciculi, which harmoniously act upon the feather quills and
collectively agitate the plumage. These are the dermal muscles. This
group is divided into two subgroups: the true dermal muscles, that is,
those that have their origin and insertion to the under surface of the
skin; and the dermo-osseous, those that originate on the surface of some
bone and insert to the inner surface of the skin.


                          TRUE DERMAL MUSCLES

                          Dermo-frontalis
                          Dermo-dorsalis
                          Dermo-tensor patagii
                          Dermo-humeralis
                          Dermo-pectoralis

=Dermo-frontalis.=[3] _Location._—This muscle is somewhat rudimentary
and may be entirely absent. It is located in the frontal region and is
about 2 or 3 centimeters long and not so wide.

Footnote 3:

  The classification of Shufeldt is used.

_Origin and Insertion._—Closely attached to the skin.

_Shape._—Flat and rather rectangular.

_Relations._—Superiorly with the skin and inferiorly with the frontal
bones.

_Action._—By contraction the feathers on the top of the head lie flat.
Those above the eyes are elevated.

=Dermo-dorsalis.= _Location._—In the median line of the neck and back.

_Origin and Insertion._—Adhering closely to the skin, it generally
becomes lost at the occiput; it is most highly developed in the
mid-cervical region, and it gradually disappears over the caudal region.

_Shape._—Delicate and ribbon-shaped.

_Relations._—Superiorly it is attached to the skin. Fat sometimes
surrounds the muscle.

_Action._—By contraction it raises the feathers along the superior part
of the neck and dorsal region.

=Dermo-tensor Patagii.= _Location._—Between the root of the neck and top
of the shoulder.

_Origin and Insertion._—Attached to the skin in the region of the
anterior part of the root of the neck, some fibers passing obliquely
upward and blend with fibers of the dermo-temporalis. It blends, by a
slender tendon, with that of the tensor patagii longus.

_Shape._—A bundle of muscular fibers later becomes thin, delicate, and
triangular in shape.

_Relations._—Externally to the skin.

_Action._—Auxiliary to the tensor patagii longus. A tensor of this
region.

The patagii are associated with the wing fold of skin which fills the
angle between the arm and forearm. This fold contains elastic tissue and
muscle.

=Dermo-humeralis.= _Location._—Lateral thoracic region.

_Origin and Insertion._—Fan-like delicate fibers from the skin in the
abdominal integument, contracting into a long narrow fasciculus of
fibers, again spreading out in fan-shape to be inserted to the tendon of
the pectoralis major, just below its insertion.

_Shape._—Triangular, fan-shape.

_Relations._—Superiorly with the skin.

_Action._—Controls the skin in this region. The anterior end being
fixed, the muscles are raised; and the posterior end acting as the fixed
point, the feathers are caused to lie close to the body.

=Dermo-pectoralis.= _Location._—On each side of the chest, lying in a
longitudinal manner.

_Origin and Insertion._—Attached to the skin on either side of the
thorax corresponding to the dermo-dorsalis. Anteriorly it disappears
over the region of the origin of the cleido-trachealis, and posteriorly
just behind the tips of the post-pubic parts of the pelvis.

_Shape._—Thin, delicate.

_Relations._—Superiorly with the skin.

_Action._—The anterior part acting as the fixed point, the feathers of
the chest are raised; and the posterior end acting as the fixed point,
the feathers are made to lie flat.


                       THE DERMO-OSSEOUS MUSCLES

                         Dermo-temporalis
                         Platysma myoides
                         Dermo-cleido dorsalis
                         Cleido-trachealis
                         Dermo-spinalis
                         Dermo-iliacus
                         Dermo-ulnaris

=Dermo-temporalis= (Fig. 18, No. 1). _Location._—From the temporal
region down the side of the neck to the anterior part of the thoracic
region.

_Origin._—By a broad tendinous attachment from a small depression above
and anterior to the temporal fossa. From here the fibers pass upward and
backward and then downward.

_Insertion._—A few fibers blend with those of the cleido-trachealis. The
fibers are then lost upon the skin in front and opposite the
shoulder-joint. Some of the fibers blend with those of the dermo-tensor
patagii.

_Shape._—Long, flat, and ribbon-shaped. The lower portion consists of
delicate fibers.

_Relations._—Superior to the temporal muscle and sphenotic process.
Superior to the cleido-trachealis and inferiorly to the shoulder-joint.
The superior portion touches the skin throughout its entire length.

_Action._—A tensor of the lateral cervical integument. It is an
auxiliary to the tensor patagii.

=Platysma Myoides.= _Location._—The inferior portion of the throat.

_Origin._—From the lower margin of the rami of the jaw. Just inferior to
the attachment of the masseter.

[Illustration:

  FIG. 18.—Muscles of the upper neck region, 1, Dermo-temporalis. 2,
    Cornu of the os hyoideum. 3, Carotid artery. 4, Jugular vein. 5,
    Pneumogastric nerve. 6, Esophagus. 7, Trachea.
]

_Insertion._—From the point of origin it spreads out into a thin
fan-like layer and meets its fellow in the median raphe. It is attached
to the skin in this region.

_Shape._—A very thin fan-shaped muscle.

_Relations._—Closely adherent to the skin.

_Action._—Assists in supporting the lingual apparatus and superior
larynx. Compresses and elevates the part.

=Dermo-cleido Dorsalis.= _Location._—Anterior shoulder region.

_Origin._—From the upper mesial part of the clavicular bone.

_Insertion._—Three fasciculi forming a fan-like arrangement attached to
the skin in the shoulder-joint and scapular region. The extremities of
the fasciculi may meet in the median line of the dorsal region and merge
with the dermo-dorsalis.

_Shape._—Three fasciculi forming a fan-shaped radiation.

_Relations._—Superiorly with the skin. Inferiorly with the
shoulder-joint.

_Action._—Contracting with the origin as the fixed point, they brace the
skin over the forepart of the back. With the integumental attachment as
the fixed point, they aid in the act of respiration.

=Cleido-trachealis.= _Location._—Extending from the shoulder to the
superior laryngeal region.

_Origin._—From a small area on the antero-inner part of the middle of
the arm of the furcula.

_Insertion._—The fibers pass upward and become flattened and attached to
the skin and dermo-temporalis muscle. They touch each other on the
anterior border of the superior larynx, the trachea, and the skin over
these parts.

_Shape._—A slender bundle of muscles.

_Relations._—Superiorly the skin, and internally the larynx and the
trachea.

_Action._—Controls the skin region of this part of the neck.

=Dermo-spinalis.= _Location._—In the region of the shoulder.

_Origin._—In an attenuated fascia from the crest of the neural spines of
the first, the second, and the third dorsal vertebræ.

_Insertion._—To the skin in a broad pale stratum, over the scapular
region.

_Shape._—Thin, pale, and very delicate.

_Relations._—Superiorly with the skin, and inferiorly with the shoulder.

_Action._—Controls the skin of the region.

=Dermo-iliacus.= _Location._—Along the back on either side of the spine.

_Origin._—From the inner angle of the marginal portion of the
antero-dorsal border of the ilium.

_Insertion._—Passing forward as a delicate band it spreads out and
becomes lost in the skin of the shoulder region.

_Shape._—Thin, delicate, and ribbon-shaped.

_Relations._—Superiorly with the skin.

_Action._—If the posterior end is fixed, it will cause the feathers to
lie close to the skin. Its action would then be opposite to the
dermo-dorsalis.

=Dermo-ulnaris.= _Location._—Outer surface of the anterior upper costal
and the posterior humeral region.

_Origin._—By a thin fascia from the outer part of the third and the
fourth true ribs at the base of their epineural appendages. Also from
the fascia between them.

_Insertion._—The fibers pass forward and upward as a thick muscular
bundle and is loosely attached to the skin at a point just back of the
humerus. The tendon later becomes spread out and attached to the fascia
as far as the elbow-joint. It covers the olecranon of the ulna.

_Shape._—At first rather thick, fascicular-like; later becomes
tendinous; and at its attachment it becomes spread out over the
olecranon.

_Relation._—Inferiorly with the ribs and humerus, and externally with
the skin.

_Action._—A depressor of the humeral region.


                          THE SKELETAL MUSCLES


                        THE MUSCLES OF THE HEAD

                         Temporal
                         Masseter
                         Biventer maxillæ
                         Entotympanicus
                         Pterygoideus internus
                         Pterygoideus externus
                         Digastricus

=Temporal= (Fig. 19, No. 4). _Location._—Occupies the temporal fossa.

_Origin._—From the mesian line of the sphenotic process, and the
adjacent wall of the orbit.

_Insertion._—The fibers passing downward and forward blend with the
fibers of the masseter. Inferiorly it inserts by a tendon to the
coranoid process upon the superior ramal margin of the mandible.

_Shape._—Fan-shaped with broad portion uppermost.

_Relations._—It occupies the temporal fossa. It is related superiorly
with the dermo-temporalis and skin. Inferiorly, with the biventer
maxillæ and the masseter.

_Action._—It aids in closing the jaw.

=Masseter= (Fig. 19, No. 1). _Location._—Occupies the supero-lateral
portion of the surface of the lower jaw.

_Origin._—In two portions: the first, by a broad and thin tendon from
the entire length of the bony ridge above the external auditory meatus,
from the squamosal process, and from the outer portion of the quadrate
bone; the second, from the side and under border of the zygoma.

_Insertion._—The first portion: The fibers pass downward and forward
beneath the zygoma; a few of the fibers blend with those of the
temporal; one tendon inserts to a small tubercle on the upper border of
the jaw behind the coronoid process, and by fleshy insertion to the
outer side of the ramus of the lower jaw, quite as far forward as the
horny portion of the beak. The second portion: by a small tendon to the
mandible on its upper border immediately in front of the articular
portion.

_Shape._—Flat, and elongate. Somewhat fleshy.

_Relations._—Superiorly with the temporal, and inferiorly with the
biventer maxillæ and stylo-hyoideus. Externally with the skin, and
internally with the jaw bone.

_Action._—Aids in closing the jaw.

=Biventer Maxillæ= (Fig. 19, No. 3). _Location._—Covers the outer
posterior portion of the mandible.

_Origin._—It arises in two portions: The first, from a ridge bounding
the posterior part of the auditory canal; the second, from a depression
of the mesial side. These two parts blend and extend downward and
forward.

_Insertion._—To the posterior part of the articular end of the mandible.

_Shape._—A curved fleshy mass.

_Relations._—Superiorly with the temporal and stylo-hyoideus.
Posteriorly with the digastricus and genio-hyoideus. Internally with the
jaw bone, and externally with the skin.

_Action._—It aids in opening the jaw.

=Entotympanic.= _Location._—Posterior to the pterygoid.

_Origin._—From the side of the basi-sphenoid and from the base of the
rostrum immediately beyond it.

_Insertion._—The fibers pass downward and forward, and insert by a
double tendinous slip. One slip inserts to a spine-like process on the
upper side of the pterygoid, and the other to the quadrato-pterygoidean
articulation.

_Shape._—Spindle-shaped.

_Relations._—Anteriorly with the pterygoid. Internally and posteriorly
with the basi-sphenoid. Externally with the pterygoideus internus.

_Action._—Aids in raising the upper mandible by pulling forward the
quadratus and pterygoidean against the palatines.

=Pterygoideus Internus= (Fig. 17, No. _B_, 5). (Synonym.—Pterygoideus
medialis.[4])

Footnote 4:

  According to international veterinary nomenclature.

_Location._—A muscular mass at the roof of the mouth.

_Origin._—From the major part of the surface of the palatine bone and
the distal head and shaft of the pterygoid and the sphenoidal
projection.

_Insertion._—By a tendon to the antero-internal part of the articular
part of the mandible.

_Shape._—Fusiform with a thick fleshy belly.

_Relations._—Superiorly with the palatine, the pterygoid, and the
sphenoid bones. Inferiorly with the skin.

_Action._—It aids in closing the jaw.

=Pterygoideus Externus.= (Synonym.—Pterygoideus lateralis.)

_Location._—Supero-external to the pterygoideus internus.

_Origin._—From the outer part of the extremity of the orbital process of
the quadrate.

_Insertion._—The fibers pass downward, outward and forward and are
inserted to the inner part of the mandibular ramus.

_Shape._—A small round bundle.

_Relations._—Inferiorly with the pterygoideus internus. Externally with
the inferior maxilla.

_Action._—Aids in closing the jaw.

=Digastricus= (Fig. 17, No. _B_, 16). _Location._—Extends from the
basi-temporal to the side of the neck.

_Origin._—From the external lateral angle of the basi-temporal.

_Insertion._—Opposite the angle of the jaw the fibers spread out in
fan-like arrangement. The muscle meets its fellow of the opposite side;
extends longitudinally over the superior larynx, for some distance down
the neck.

_Shape._—Thin and ribbon-shaped.

_Relations._—Externally to the platysma myoides. The anterior fasciculi
blend with those of the mylo-hyoideus; internally with the larynx at the
upper part.

_Action._—To raise the trachea and hyoid apparatus against the pharynx.


                       THE MUSCLES OF THE TONGUE

                          Mylo-hyoideus
                          Stylo-hyoideus
                          Genio-hyoideus
                          Cerato-hyoideus
                          Sterno-hyoideus
                          Depressor-glossus
                          Cerato-glossus
                          Hyoideus transversus

=Mylo-hyoideus.= _Location._—The forepart of the inter-ramal space.

_Origin._—From the inner side of the lower jaw at a point just above the
lower border and the inturned edge of the horny sheath of the beak.

_Insertion._—By aponeurosis to the under side of the hyoid, on the
median line between the first and the second basi-branchial.

_Shape._—Thin, flat, and delicate.

_Relations._—Inferiorly with the skin. Thin and rather broad, it meets
its fellow of the opposite side. Laterally with the rami of the jaw.
Superiorly with the hyoid apparatus.

_Action._—Lifts the tongue upward against the roof of the mouth.

=Stylo-hyoideus= (Fig. 17, No. _B_, 6). _Location._—Supero-posterior to
the hyoid apparatus.

_Origin._—From the outer portion of the articular enlargement of the
lower jaw.

_Insertion._—By a tendon to the basi-branchial of the thyro-hyal.

_Shape._—A long transversely flattened fasciculus.

_Relations._—Supero-posterior part of the hyoid apparatus along side the
genio-hyoideus and the cerato-hyoideus.

_Action._—Singly, pulls the tongue to one side; acting with its fellow,
pulls the tongue upward.

=Genio-hyoideus= (Fig. 9, No. 7). _Location._—Supero-posterior to the
hyoid apparatus.

_Origin._—From the anterior portion of the inner side of the lower jaw.

_Insertion._—To the middle of the outer side of the basi-branchial of
the corner of the os hyoides which cornu it completely envelops.

_Shape._—A long, rather thick fasciculus.

_Relations._—With the stylo-hyoideus and cerato-hyoideus.

_Action._—Protrudes the tongue from the mouth.

=Cerato-hyoideus= (Fig. 9, No. 8). (Synonym.—Kerato-hyoideus.)

_Location._—Inferior to the hyoid apparatus.

_Origin._—By a delicate tendinous slip from the under side of the shaft
of the basi-hyal element of the hyoid apparatus.

_Insertion._—To a small elevation on the under side of the anterior end
of the glosso-hyal.

_Shape._—A small round muscular fasciculus becoming tendinous in its
anterior half.

_Relations._—Superiorly with the hyoid apparatus.

_Action._—Singly, pulls the tongue to one side; acting with its fellow,
depresses the tongue.

=Sterno-hyoideus.= _Location._—Inferior to the hyoid apparatus.

_Origin._—From the outer anterior surface of the thyroid bone of the
superior larynx.

_Insertion._—To the anterior part of the basi-hyal.

_Shape._—At first broad and rather fleshy, becomes contracted and
somewhat tendinous.

_Relations._—Inferior to the hyoid apparatus and superior larynx.

_Action._—When the larynx is fixed, acting alone deflects the tongue
laterally; acting with its fellow, depresses the tongue. If the base of
the tongue is fixed the two pull the larynx forward. Hence muscles of
deglutition.

=Depressor-glossus.= _Location._—Superior to the basi-hyal.

_Origin._—From the under portion of the basi-hyal.

_Insertion._—To under part of the glosso-hyal.

_Shape._—Small, short.

_Relations._—Superiorly with the basi-hyal and glosso-hyal bones.

_Action._—Depresses the tip of the tongue and elevates the base.

=Cerato-glossus.= _Location._—On the upper portion of the cornu of the
hyoid.

_Origin._—One-half of the surface of the first basi-branchial.

_Insertion._—To the upper side of the shaft of the cerato-branchial
element of the hyoid apparatus.

_Shape._—A small muscular fasciculus.

_Relations._—Supero-laterally to the cerato-branchial element.

_Action._—Elevates the cornua of the hyoid arches and presses them
against the skull.

=Hyoideus Transversus= (Fig. 9, No. 9 and 10). _Location._—Envelops the
spur process of the euro-hyal.

_Origin and Insertion._—It extends from the inner side of one cornu to
the spur process.

_Shape._—Thin, flat.

_Relations._—Posterior to the euro-hyal, which it envelops, and between
the cornua of the os hyoides.

_Action._—Approximates the cornua of the os hyoides.


                          THE CERVICAL MUSCLES

                     Complexus
                     Rectus capitis anticus minor
                     Flexor capitis inferior
                     Rectus capitis posticus major
                     Biventer cervicis
                     Longus colli posticus
                     Obliquus colli
                     Longus colli anterior
                     Rectus capitis lateralis
                     Trachelo-mastoideus
                     Interspinales
                     Interarticulares
                     Obliquo-transversales
                     Intertransversales
                     Scalenus medius

=Complexus= (Fig. 19, No. 5). _Location._—Supero-lateral portion of the
neck.

_Origin._—By three tendinous slips from the antero-lateral portion of
the transverse process of the fourth, the fifth, and the sixth cervical
vertebræ.

_Insertion._—The muscular fibers pass around the neck and meet their
fellows in the median line in a fascia formation. The thin tendinous
sheet inserts into the occiput just above the occipital ridge.

_Shape._—From point of origin this muscle expands into a broad sheet.

_Relations._—It overlies the muscles of the occipital region.

_Action._—It extends the head.

=Rectus Capitis Anticus Minor= (Fig. 19, No. 8). (Synonym.—Rectus
capitis ventralis minor.)

_Location._—Infero-lateral portion of the neck.

_Origin._—From the apices of the hyapophyses of the second, the third,
and the fourth cervical vertebræ.

_Insertion._—To the occiput just below the complexus.

_Shape._—A long and rather thick fasciculus.

_Relations._—Externally with the skin. The tendinous slips of origin
pass between the flexor capitis inferior and longus colli anterior.

_Action._—Extends the head.

=Flexor Capitis Inferior= (Fig. 19, No. 7). _Location._—Antero-inferior
part of the neck.

_Origin._—From the apices of the hyapophyses of the second, the third,
and the fourth cervical vertebræ.

_Insertion._—To the triangular area on the basi-temporal of the base of
the cranium.

_Shape._—At first tendinous, becomes somewhat fleshy as it passes
forward.

[Illustration:

  FIG. 19.—Muscles of the head and neck. 1, Masseter muscle. 2,
    Infraorbital sinus. 3, Biventer maxilla. 4, Temporalis. 5,
    Complexus. 6, Rectus capitis posticus major. 7, Flexor capitis
    inferior. 8, Rectus capitis anticus minor. 9, Biventer cervicis. 10,
    Longus colli posticus. 11, Obliquus colli. 12, Intertransversales.
    13, Longus colli anterior. 14, Lateral temporo-maxillary ligament.
    15, Lateral ligament of the jaw. 16, Trachelo-mastoideus. 17, Rectus
    capitis lateralis. 18, Scalenus medius. 19, Rhomboideus. 20,
    Trapezius. 21, Location of scapula. 22, Supraspinatus. 23, Teres et
    Infraspinatus.
]

_Relations._—Antero-inferior portion of the neck close to the rectus
capitis anticus minor.

_Action._—Flexes the head upon the neck.

=Rectus Capitis Posticus Major= (Fig. 19, No. 6). (Synonym.—Rectus
capitis dorsalis major.)

_Location._—Supero-lateral area on the anterior portion of the neck.

_Origin._—From the median anterior aspect of the second cervical
vertebra, and the supero-anterior border of the neural canal.

_Insertion._—To the crescent-shaped area at the back of the skull.

_Shape._—Short, thick, fleshy bundle.

_Relations._—Superiorly with the complexus; inferiorly with the
trachelo-mastoideus and the vertebræ.

_Action._—Singly, pulls the head to one side; acting with its fellow,
extends the head.

=Biventer Cervicis= (Fig. 19, No. 9). _Location._—Occupies the superior
part of the neck.

_Origin._—From the side of the neural spine of the first dorsal
vertebra, and from the adjacent tendon of the longus colli posticus.

_Insertion._—To the occiput.

_Shape._—Tendinous in the middle with a more or less spindle-shaped
belly at each end.

_Relations._—Superior to the longus colli posticus. It lies next to the
skin.

_Action._—Extends the head on the neck and elevates the neck.

=Longus Colli Posticus= (Fig. 19, No. 10). (Synonym.—Longus colli
dorsalis.)

_Location._—Occupies the superior part of the neck.

_Origin._—From the marginal edges of the summits of the neural spines of
the first two dorsal vertebræ.

_Insertion._—To the transverse process of the axis, and superior part of
the cervical vertebræ.

_Shape._—A long, somewhat narrow, flattened muscle, the inferior portion
of which is divided into five or six fasciculi.

_Relations._—Superiorly with the biventer cervicis and inferiorly with
the vertebræ.

_Action._—Raises the neck upward.

=Obliquus Colli= (Fig. 19, No. 11). _Location._—On the lateral side of
the neck.

_Origin and Insertion._—The first of the seven fasciculi originates from
the diapophysis of the eleventh cervical vertebra, winds obliquely over
the tenth, and is inserted into the posterior margin of the
postzygapophysis of the ninth vertebra. In its passage it receives the
slip from the longus colli posticus. The next fasciculus originates from
the transverse process of the tenth cervical vertebra, winds obliquely
over the ninth vertebra, and is inserted to the postzygapophysis of the
eighth vertebra. In its passage it also receives a fasciculus from the
longus colli posticus. The next three fasciculi originate in a similar
manner being attached to similar postzygapophyses and have slips
extending forward which slips are inserted to the neural spines of the
alternate vertebræ. The sixth fasciculus originates from the transverse
process of the sixth vertebra, passing obliquely up the neck is inserted
to the extremity of the diapophysis of the fourth vertebra, the outer
extremity of the transverse process of the third vertebra. The seventh,
or anterior, fasciculus originates from the transverse process of the
fifth vertebra, and is inserted to the extremity of the diapophysis of
the third vertebra.

_Shape._—Short, thick fasciculi.

_Relations._—Laterally with the vertebræ. Inferiorly with the
intertransversales. Superiorly with the longus colli posticus, and
externally with the skin.

_Action._—Flexes one vertebra on the other laterally.

=Longus Colli Anterior= (Fig. 19, No. 13). (Synonym.—Longus colli
ventralis.)

_Location._—Occupies the anterior portion of the neck.

_Origin and Insertion._—This muscle is divided into a vertical portion,
and a superior and an inferior oblique portion. The vertical portion
originates from the hypophyses of the tenth to the fifteenth vertebra
and is inserted by a tendon to the tubercle on the inferior portion of
the atlas. Small, slender tendons are given off and insert to the apices
of the parapophyses of the fourth to the tenth cervical vertebræ. There
is more or less attachment to the bodies of the cervical vertebræ
mentioned. The superior oblique portion originates from the diapophyses
of the third, the fourth, the fifth cervical vertebræ and becoming
tendinous is inserted to the tubercle on the inferior portion of the
body of the atlas. The inferior oblique portion originates from the
transverse processes of the fourth, the fifth, and the sixth cervical
vertebræ. It is inserted by a slender tendon to the apex of the
parapophysis of the third cervical vertebra.

_Shape._—A long fleshy muscle extending the entire length of the neck.

_Relations._—Inferiorly with the skin and superiorly with the cervical
vertebræ.

_Action._—Pulls the neck downward.

=Rectus Capitis Lateralis= (Fig. 19, No. 17). _Location._—The
infero-lateral anterior portion of the neck.

_Origin._—Originates tendinous from the diapophysis of the third, the
fourth, and the fifth cervical vertebræ.

_Insertion._—Passes obliquely upward in front of the spinal column to
the inner tubercle on the basal ridge of the basi-temporal bone, by a
subcompressed tendon.

_Shape._—A somewhat thick fasciculus.

_Relations._—Superiorly with the trachelo-mastoideus, inferiorly with
the longus colli anterior, and externally with the skin.

_Action._—Singly, pulls the head down and to one side; acting with its
fellow, pulls the head downward.

=Trachelo-mastoideus= (Fig. 19, No. 16). (Synonym.—Longissimus capitis
et atlantis.)

_Location._—Laterally on the anterior portion of the neck.

_Origin._—Semitendinous from the diapophyses of the second, the third,
the fourth, and the fifth cervical vertebræ.

_Insertion._—By subcompressed tendon to the base of the cranium, at the
outer tubercle of the basal ridge of the basi-temporal.

_Shape._—Flattened from side to side; broad at the posterior portion,
becomes angular at the anterior portion.

_Action._—Singly, pulls the head down and to one side; acting with its
fellow, pulls the head downward.

=Interspinales= (Fig. 17, _A_, No. 2). _Location._—Superior to the
vertebra.

_Origin and Insertion._—A series of muscles connecting the superior
neural spines of the cervical vertebræ.

_Shape._—Thin, flat.

_Relations._—Anteriorly the posterior border of the vertebræ in front
and posteriorly the anterior border of the succeeding vertebræ,
inferiorly by the vertebræ.

_Action._—To approximate the spinous portion of the vertebræ.

=Interarticulares= (Fig. 17, No. _A_, 4). _Location._—Supero-laterally
to the vertebræ. Between the postzygapophysis.

_Origin and Insertion._—From the posterior margin of the ring of the
atlas to the postzygapophysis of the axis. Then in the succeeding
vertebræ from the postzygapophysis of the vertebra to the same of the
succeeding vertebra.

_Shape._—Muscular bundle.

_Relations._—Inferiorly with the vertebræ. Supero-laterally with the
obliquo-transversales.

_Action._—Aids in approximating the vertebræ in a supero-lateral
direction.

=Obliquo-transversales= (Fig. 17, _A_, No. 1).
_Location._—Supero-lateral to the vertebræ.

_Origin and Insertion._—Passes obliquely from the transverse process of
one vertebra to the postzygapophysis of the vertebra beyond.

_Shape._—A thin fasciculus.

_Relations._—Inferiorly with the interarticulares and laterally with the
intertransversales.

_Action._—Aids in flexing the vertebræ supero-laterally.

=Intertransversales= (Fig. 19, No. 12). _Location._—Laterally to the
vertebræ.

_Origin and Insertion._—Extend between the transverse processes
beginning at the third cervical vertebra.

_Shape._—Short, thick.

_Relations._—Laterally the vertebræ. Superiorly the
obliquo-transversales.

_Action._—Aids in flexing the vertebræ laterally.

=Scalenus Medius= (Fig. 19, No. 18). (Synonym.—Scalenus.)

_Location._—Supero-laterally to the entrance of the thorax.

_Origin._—From the diapophysis and pleurapophysis of the eleventh
cervical vertebra.

_Insertion._—To the entire border of the first rib. A few fibers pass
over to the anterior free margin of the middle third of the second rib.

_Shape._—Rather pyramidal in shape with base uppermost.

_Relations._—Posteriorly with the levatores costarum. Internally with
the longus colli.

_Action._—When the first rib is fixed singly, turns the neck to one
side; acting with its fellow, extends the neck. When the neck is fixed,
by drawing the first rib forward, it acts as an inspiratory muscle.


                    THE MUSCLES OF THE AIR PASSAGES


                          The Superior Larynx

                         Constrictor glottidis
                         Thyreo-arytenoideus


                          The Inferior Larynx

                      Tracheo-lateralis
                      Broncho-trachealis posticus
                      Broncho-trachealis anticus
                      Broncho-trachealis brevis
                      Bronchialis posticus
                      Bronchialis anticus
                      Sterno-trachealis

=Constrictor Glottidis.= _Location._—Supero-anterior portion of the
superior larynx.

_Origin._—From the superior and longitudinal line of the thyroid plate.

_Insertion._—All along the inner margin of the arytenoid bone, and to
the apex of the mid-cricoidal segment.

_Shape._—Thin, flat sheet extending outward and upward, and then inward.

_Relation._—Interiorly with the larynx.

_Action._—The two muscles of this kind acting together, close the
glottis by drawing the apices of the arytenoids to the median line.

=Thyreo-arytenoideus.= _Location._—Supero-lateral portion of the
superior larynx.

_Origin._—From the entire outer margin of the thyroid plate and the
outer margin of the cricoid bone.

_Insertion._—All along the outer margin of the arytenoid bone and the
outer border of the central cricoid piece.

_Shape._—A thin, flat sheet.

_Relations._—Infero-laterally with the superior larynx.

_Action._—The two muscles of this kind acting together, open the glottis
by pulling the arytenoid bone outward.

=Tracheo-lateralis= (Fig. 20, No. 2). _Location._—Along the lateral side
of the trachea.

_Origin._—By the union of the bronchio-trachealis posticus and
bronchio-trachealis anticus, on the lateral side of the trachea, about
1½ centimeters from the bifurcation of the trachea.

_Insertion._—In delicate fan-like structure to the side of the trachea,
near the superior larynx.

_Shape._—Thin, ribbon-shaped, closely attached to the trachea.

_Relations._—Internally with the trachea, and externally with the skin
and other integument.

_Action._—Acts as a brace to the sides of the trachea, and contracting,
approximates the tracheal rings and thus shortens the trachea.

=Broncho-trachealis Posticus= (Fig. 21, No. 3).
_Location._—Postero-superior portion of the trachea. The fibers pass
downward and backward.

_Origin._—From the inferior end of the tracheo-lateralis.

_Insertion._—To the end of the third half of the bronchial ring of the
same side.

_Shape._—A small fasciculus.

_Relations._—Internally with the trachea, and externally with the skin
and other integument.

[Illustration:

  FIG. 20.—The anterior pectoral region. 1, Sterno-trachealis. 2,
    Tracheo-lateralis. 3, Broncho-trachealis brevis. 4, Costal process
    of sternum. 5, Right and left carotid converging and occupying same
    sheath at 6. 7, The heart showing branches of coronary artery. 8,
    Cervical air-sac. 9, Left brachio-cephalic artery. 10, Right
    brachio-cephalic artery. 11, Trachea. 12, Inferior larynx. 13.
    Subclavian artery. 14, Carotid trunk. 15, Internal thoracic artery.
    16 Thyroid gland. 17, Anterior vena cava. 18, Auricular appendage.
]

[Illustration:

  FIG. 21.—The inferior tracheal region. 1, Bronchialis anticus. 2,
    Bronchialis posticus. 3, Broncho-trachealis posticus. 4,
    Broncho-trachealis anticus.
]

_Action._—A tensor of the true or inferior larynx.

=Broncho-trachealis Anticus= (Fig. 21, No. 4). _Location._—Anterior
portion of the inferior extremity of the trachea.

_Origin._—The anterior branch of the bifurcated tracheo-lateralis.

_Insertion._—To the anterior extremity of the third half ring of the
bronchus of the same side.

_Shape._—A small fasciculus.

_Relations._—Internally with the trachea, and externally with the skin
and other integument.

_Action._—A tensor of the inferior larynx.

=Broncho-trachealis Brevis= (Fig. 20, No. 3). _Location._—Posterior part
of the inferior extremity of the trachea.

_Origin._—From just beneath the broncho-trachealis anticus muscle.

_Insertion._—Extends obliquely across the inferior larynx and is
inserted to the posterior end of the second bronchial ring.

_Shape._—Rather short, strong, straight, subcylindrical.

_Relations._—Internally with the trachea, and laterally with the
broncho-trachealis posticus.

_Action._—A tensor of the inferior larynx.

=Bronchialis Posticus= (Fig. 21, No. 2). _Location._—Supero-lateral side
of the anterior end of the bronchi.

_Origin._—From the lateral inferior margin of the last tracheal ring.

_Insertion._—Passing obliquely across the larynx it inserts to the
posterior extremity of the second half ring of the bronchus.

_Shape._—Small, thick, spindle-shaped.

_Relations._—Internally with the trachea, inferiorly with the
bronchialis anticus, and superiorly with the broncho-trachealis brevis.

_Action._—A tensor of the larynx.

=Bronchialis Anticus= (Fig. 21, No. 1). _Location._—Inferior to the
former muscle.

_Origin._—From the last ring of the trachea.

_Insertion._—The fibers pass obliquely forward and become inserted to
the rim of the arytenoid cartilage of the inferior larynx, and the
anterior extremities of the first and second half rings of the bronchus.

_Shape._—Thick, spindle-shaped; about twice the size of the bronchialis
posticus.

_Relations._—It is crossed at its origin by the broncho-trachealis
anticus and is related internally with the bronchus and end of the
trachea.

_Action._—A tensor of the larynx.

=Sterno-trachealis= (Fig. 20, No. 1). _Location._—The inferior region of
the trachea above the above-named muscles.

_Origin._—From the side of the trachea beneath the posterior border of
the broncho-trachealis anticus.

_Insertion._—Passes downward and backward across the cavity of the chest
and is inserted to the inner part of the costal process of the sternum.

_Shape._—A delicate cord of fibers.

_Relations._—Internally with the broncho-trachealis muscles.

_Action._—A relaxor of the larynx, and hence, of the tympanic membrane.


                           THE STERNAL GROUP

=Triangularis Sterni.= _Location._—In the floor of the thoracic cavity.

_Origin._—From the entire superior margin of the summits of the costal
processes.

_Insertion._—The fibers extend upward and backward, dividing into four
digitations which cover the inner surface of the three principal sternal
ribs, and are inserted to the first four as high as their articulations
with the vertebral ribs.

_Shape._—Flat and somewhat triangular.

_Relations._—Interiorly with the floor of the thoracic cavity.

_Action._—A powerful muscle of expiration. In contracting, lessens the
cubic content of the thorax.

=The Diaphragm= (Fig. 47, No. 10; Fig. 33, No. 9). _Description._—The
diaphragm in the domestic fowl is rudimentary. It consists of a thin
semi-transparent membrane, situated between and separating the thoracic
and the abdominal cavities. It readily conforms to the various organs
pressing upon it from each side. On each side are three rudimentary
muscles which extend from the vertebral heads of the second, the third,
and the fourth sternal ribs. The fibers of these muscles spread out in
fan-like upon the diaphragm, and are seen just above the digitations of
the triangularis sterni.


                         THE ABDOMINAL MUSCLES

                      Obliquus abdominis externus
                      Obliquus abdominis internus
                      Rectus abdominis
                      Transversalis abdominis

=Obliquus Abdominis Externus= (Fig. 22, No. 1). _Location._—The
outermost muscle of the lateral abdominal wall.

_Attachments._—By a delicate aponeurotic membrane, from the sides of all
the true dorsal ribs, from the posterior border of the last vertebral
rib and the adjoining margins of the pelvis, and from the entire
posterior surface of the inferior border of the post-pubic element of
the pelvis; by aponeurosis, blending with the fascia toward the root of
the tail and lower part of the abdomen; and by aponeurosis to the sides
of the sternum, to the under part of the pectoralis major muscle, and to
the zyphoid prolongation. Also by aponeurosis it meets its fellow from
the opposite side, at the linea alba.

[Illustration:

  FIG. 22.—The abdominal muscles of a hen. Right side. 1, Obliquus
    abdominis externus. 2, Obliquus abdominis internus. 3, Peritoneum
    covering intestines. 4, Peritoneum covering the gizzard. 5, The
    lungs (note how small they are from a relative standpoint). 6, The
    great sciatic or ischiadic nerve. 7, Lumbar nerves. 8, Kidney. 9,
    Brachial plexus. 10, Pericardium of the base of the heart. 11,
    Anterior vena cava. 12, Oil gland. 13, Showing a sacculation of the
    abdominal muscles. There is no tunica abdominalis in the fowl.
]

=Obliquus Abdominis Internus= (Fig. 22, No. 2). _Location._—Just
internal with regard to the external oblique.

_Attachments._—By aponeurosis, from the posterior third of the
post-pubic element of the pelvis; by muscular fibers, from the balance
of the bone; and by a few fibers, from the iliac border posterior to the
acetabulum. Anteriorly, these fibers are inserted to the entire
posterior margin of the last vertebral rib, and into the pleurapophysial
head of the last costal rib.

=Rectus Abdominis= (Fig. 13, No. 10 and Fig. 23, No. 1). _Location._—The
inferior median abdominal wall.

_Attachments._—By aponeurosis, from the distal extremity of the
post-pubic element of the pelvis and from the semitendinous ligament
which stretches from one post-pubic tip to the other. Attaches
anteriorly to the zyphoid margin of the sternum, and passes, by a broad
aponeurotic membrane, over the outer surface of the thoracic wall
beneath the external oblique.

=Transversalis Abdominis= (Fig. 25, No. _H_, 1).
_Location._—Infero-lateral portion of the abdominal wall.

_Attachments._—By a thin, tendinous attachment from the entire
post-pubic and iliac margins of the pelvis and from the interpubic
ligament. Its fibers cross the abdomen between the peritoneum, the
rectum, and the internal oblique. It is inserted over the entire pleural
part of the last two vertebral ribs, the intercostal muscles between
them, and the same surface of the hemapophyses connected below. Inserts
into the linea alba.

_Action._—The abdominal muscles give support to the abdominal organs,
aid in flexing the spine, draw the last rib backward, thus aiding in
respiration, and compress the abdominal organs to aid in defecation and
expiration.


                        THE DORSO-LUMBAR REGION

                           Sacro-lumbalis
                           Longissimus dorsi

=Sacro-lumbalis.= _Location._—The lateral lumbo-sacral region.

_Origin._—Tendinous from the anterior margin of the ilium, from the
angles of the last two vertebral ribs, and by tendinous slips, from the
outer ends of the transverse processes of the last three dorsal
vertebræ.

_Insertion._—By a few fleshy fibers into the angle of the first dorsal
rib and to the corresponding points upon the free cervical ribs, and by
a strong semitendinous insertion into the outer extremity of the
diapophysis of the twelfth cervical vertebra.

_Shape._—A close fitting, tendo-muscular sheet extending between the
anterior margin of the ilium and the root of the neck.

_Relations._—Intimately blended with the longissimus dorsi externally.

_Action._—Assists the longissimus dorsi.

=Longissimus Dorsi= (Fig. 24, No. 4). _Location._—The superior
dorso-lumbar region.

_Origin._—From the inner portion of the anterior margin of the ilium,
and from the various surfaces afforded by its walls and the walls of the
ilio-neural canal; by a series of short and distinct tendons alternately
from the anterior and posterior extremities of the summits of the neural
spines of all the dorsal vertebræ. From the diapophyses of the dorsal
vertebræ, from the crests of the neural spines of the last three dorsal
vertebræ, from the bodies of the dorsal vertebræ, and from the fascia
between them and the sacro-lumbalis; and also by a tendinous sheet
continuous with the origin of the longus colli posticus.

_Insertion._—By four fasciculi into the free posterior margins of the
oblique processes of the eleventh, the twelfth, the thirteenth, and the
fourteenth cervical vertebræ.

_Shape._—A large flat sheet.

_Relations._—Laterally, with the superior spinous processes of the
vertebræ, and with the superior surface of the ribs.

_Action._—Singly, flexes the back laterally; with its fellow, aids in
elevating the body upward.


                         THE COCCYGEAL MUSCLES

                          Levator coccygis
                          Levator caudæ
                          Transversus peronei
                          Depressor caudæ
                          Depressor coccygis
                          Lateralis caudæ
                          Lateralis coccygis
                          Infracoccygis

=Levator Coccygis= (Fig. 23, No. 2). _Location._—The superior part of
the caudal apparatus.

_Origin._—From a limited area of the ilium just beyond and to the side
of the anterior free caudal vertebræ.

_Insertion._—Into the tuberosity of the anterior margin of the
pygostyle.

_Shape._—Short, fleshy.

_Relations._—Superior portion of the coccygeal vertebræ.

_Action._—Elevates the tail.

=Levator Caudæ= (Fig. 23, No. 4). _Location._—Supero-lateral side of the
tail.

_Origin._—From the posterior surface of the post-acetabular area of the
pelvis, and from the superior surface of all the coccygeal vertebræ
except the pygostyle.

_Insertion._—To the four inner quill butts of the main tail feathers.

_Shape._—Long, spindle-shaped.

_Relations._—Internally, with the levator coccygis and externally, with
the lateralis caudæ.

_Action._—Powerfully elevates the four inner main tail feathers.

=Transversus Peronei= (Fig. 23, No. 3). _Location._—The posterior
abdominal region.

[Illustration:

  FIG. 23.—Outer layer of muscles of the tail and thigh, 1, Rectus
    abdominis. 2, Levator coccygis. 3, Transversalis peronie. 4, Levator
    caudæ. 5, Lateralis caudæ. 6, Depressor caudæ. 7, Sartorius. 8 and
    9, Gluteus primus. 10, Semitendinosus. 11, Gastrocnemius. 12,
    Peroneus longus. 13, Flexor perforatus indicis secundus pedis. 14,
    Flexor perforatus medius secundus pedis. 15, Lateral ligament of the
    hock.
]

_Origin._—From the entire posterior margin of the ischium, and from the
posterior margin of the post-pubis extending beyond it.

_Insertion._—Becoming aponeurotic, it passes toward the coccyx and is
attached to the entire posterior margin of the ilium. Passes to the
median line, meeting its fellow in front of the anus.

_Shape._—Thin, sheet-like.

_Relations._—Infero-anteriorly with the anus. Posteriorly with the edges
of the ilium and of the ischium. Internally with the depressor caudæ.

_Action._—Gives support to the viscera in the post-anal region, and aids
in attaching the anus to the structures above.

=Depressor Caudæ= (Fig. 23, No. 6). _Location._—The infero-lateral side
of the tail.

_Origin._—From the lower half of the posterior border of the ischium,
and from the entire posterior border of the post-pubis beyond.

_Insertion._—To the quill butts of the three or four outer main tail
feathers.

_Shape._—Strong, conical.

_Relations._—Externally, with the depressor coccygis.

_Action._—Singly, pulls the tail downward and outward; with its fellow,
pulls the tail downward.

=Depressor Coccygis.= _Location._—The outermost of the infero-lateral
muscles of the tail.

_Origin._—From the lower half of the posterior margin of the ischium and
the anterior three-fourths of the posterior margin of the post-pubic
element of the pelvis beyond it.

_Insertion._—To the thickened rim of the inferior and expanded portion
of the pygostyle.

_Shape._—Flat, triangular.

_Relations._—Internally with the depressor caudæ.

_Action._—Singly, pulls the tail downward and to one side; with its
fellow, pulls the tail downward.

=Lateralis Caudæ= (Fig. 23, No. 5). _Location._—The lateral side of the
tail.

_Origin._—From the tip of the transverse process of the first free
caudal vertebræ.

_Insertion._—To the outer three quill butts of the main tail feathers.

_Shape._—Four fasciculi forming a fleshy belly.

_Relations._—Inferiorly, with the levator caudæ and superiorly with the
depressor caudæ.

_Action._—Singly, pulls the tail downward and outward; with its fellow,
pulls the tail downward. The outermost fasciculus contracting, spreads
the tail feathers.

=Lateralis Coccygis= (Fig. 25, No. _E_, 2). _Location._—The
infero-lateral side of the caudal vertebræ.

_Origin._—From the surface of the posterior end of the ilium and by
tendons from the under side of the ends of the first three or four
caudal vertebræ.

_Insertion._—To the side of the posterior margin of the expanded portion
of the pygostyle.

_Shape._—Subcompressed mass.

_Relations._—With the transverse processes of the caudal vertebra,
inferiorly.

_Action._—Controls the lateral movements of the tail and its feathers,
and the oblique downward movement.

=Infracoccygis= (Fig. 25, No. _E_, 1). _Location._—The extreme inferior
portion of the caudal vertebræ.

_Origin._—From the inferior surface of the diapophysis of the last
vertebra which anchyloses with the pelvic sacrum, and from all the free
caudal vertebræ.

_Insertion._—Into the lower side of the pygostyle.

_Shape._—Flat, somewhat triangular.

_Relations._—Superiorly, with the vertebræ, laterally, with the
lateralis coccygis, and mesially, with its fellow of the opposite side.

_Action._—Depresses the tail.


                           THE COSTAL REGION

                        Latissimus dorsi
                        Trapezius
                        Rhomboideus
                        Serratus magnus anticus
                        Serratus parvus anticus
                        Teres et infraspinatus
                        Intercostales
                        Levatores costarum
                        Appendico-costales

=Latissimus Dorsi= (Fig. 24, No. 7). _Location._—Supero-lateral portion
of the dorsal region.

_Origin._—From two portions, the anterior slip from the outer edge of
the superior margins of the neural spines of the second and the third
dorsal vertebræ, and the second portion from a similar point on all the
succeeding dorsal vertebræ. The second portion is fascia-like in its
attachments.

_Insertion._—The fibers converge toward the humerus and enter between
the deltoid the scapular head of the triceps and the remaining heads of
this muscle and is inserted to the anconal part of the humerus, just
within in the radial crest.

_Shape._—Thin, triangular.

_Relations._—Superiorly, with the skin. The most superficial of the
dorsal muscles.

_Action._—To elevate the humerus and thus flex the shoulder-joint. An
expiratory muscle when the wing is fixed.

=Trapezius= (Fig. 19, No. 20). _Location._—In the shoulder region, just
below the longissimus dorsi.

_Origin._—From the neural spines of the second, the third, the fourth,
and the fifth cervical vertebræ just below the latissimus dorsi.

_Insertion._—To the mesian upper border of the scapula.

_Shape._—A flat oblong layer of fibers.

_Relations._—The posterior part of the trapezius overlies the anterior
part of the rhomboideus. The posterior two-thirds is covered by the
latissimus dorsi. The anterior third is superficial.

_Action._—Draws the scapula forward.

=Rhomboideus= (Fig. 19, No. 19). _Location._—Supero-posterior scapular
region.

_Origin._—From the neural spines of the first four dorsal vertebræ
beneath the latissimus dorsi and trapezius muscles.

_Insertion._—The fibers passing outward and backward attach to the
posterior third of the mesial or upper border of the scapula.

_Shape._—Thin, flat, delicate.

_Relations._—Superiorly, by the latissimus dorsi and the trapezius.

_Action._—To draw the free end of the scapula upward and forward.

=Serratus Magnus Anticus= (Fig. 13, No. 16). _Location._—The
supero-lateral side of the thorax.

_Origin._—By three strong digitations: first, from the outer part of the
second true rib just above the base of the epineural appendage; the
other two, from similar locations on the two succeeding ribs, just above
the origin of the dermo-ulnaris.

_Insertions._—The first by tendinous attachment to the
interpleurapophysial membrane. The rest of the fibers pass upward and
slightly forward, and are inserted to the inferior surface of the apex
of the scapula.

_Shape._—Three flat, strong digitations.

_Relations._—Internally, with the ribs.

_Action._—If the scapula is fixed, it is a muscle of inspiration.

=Serratus Parvus Anticus.= _Location._—The outer and upper surface of
the anterior part of the thorax.

_Origin._—By three digitations from the outer surface of the first three
ribs above the origin of the serratus magnus anticus and the
thoraco-scapularis.

_Insertion._—The thin sheet of fibers passes upward and backward, and is
inserted to the inferior margin of the scapula.

_Shape._—Thin, flat.

_Relations._—Internally, with the ribs.

_Action._—If the scapula is fixed, it is a muscle of respiration.

=Teres et Infraspinatus= (Fig. 13, No. 11). _Location._—Scapular region.

_Origin._—From the superior surface and outer margin of the posterior
two-thirds of the scapula.

_Insertion._—The fibers pass forward and outward, and insert to the
humerus at the middle of the ulnar margin of the pneumatic fossa,
between the forks of the triceps.

_Shape._ —Flat, triangular-shaped.

_Relations._—Anteriorly, with the supraspinatus. Internally, with the
ribs.

_Action._—Aids in keeping the humerus in its socket. Assists in closing
the wing by drawing the humerus to the side of the body.

=Intercostales= (Fig. 24, No. 5). _Location._—Between the ribs of the
upper thoracic region.

_Origin and Insertion._—From the anterior border of one rib, the fibers,
passing obliquely upward and forward, and the lower portion downward and
forward, are inserted to the posterior border of the rib just in front.

_Shape._—They are best developed in the anterior portion of the thoracic
region and extend down as far as the sternal ribs.

_Relations._—Internally the pleura, and anteriorly and posteriorly the
ribs.

_Action._—The first rib being rendered fixed by the scalenus medius, the
muscles draw the ribs forward, thus aiding inspiration.

=Levatores Costarum= (Fig. 24, No. 2). _Location._—Supero-lateral
portion of the thorax.

_Origin and Insertion._—A series of muscles, the first of which extends
from the extremity of the transverse process of the twelfth vertebra,
the fibers passing downward and backward to the anterior free margin of
the upper third of the long posterior rib, and to the external surface
close to its margin. The others arise and insert in a similar manner
from the ends of the diapophyses of all the dorsal vertebræ and attach
to each succeeding rib. Those in front are best developed.

_Shape._—Thin and triangular.

_Relations._—External to the intercostales.

_Action._—Aids in respiration.

=Appendico-costales= (Fig. 24, No. 1). _Location._—The lateral side of
the thorax.

_Origin and Insertion._—From the posterior edge of an uncinate process
or epineural appendage, the fibers extending downward and backward to
the outer surface of the succeeding rib.

_Shape._—A series of thin triangular-shaped muscles.

_Relations._—Internally, with the intercostales.

_Action._—Aids in respiration.


                      THE ANTERIOR PECTORAL GROUP

                         Tensor patagii longus
                         Tensor patagii brevis

=Tensor Patagii Longus= (Fig. 15_C_, No. 1; Fig. 14, No. 2).
_Location._—Anterior shoulder region, in the triangular patagium of the
wing.

_Origin._—By a flat tendon common to it and the tensor patagii brevis
from the supero-mesial line of the head of the clavicle.

_Insertion._—By a long slender tendon extending in the duplicature of
the patagium, with which the fibers blend. Passing to the side of the
extensor metacarpi radialis longus, it extends over the end of the
radius and is inserted to the os carpi radiale, and to the fascia which
binds down the other tendons on the anterior part of the wrist-joint.

_Shape._—Cone-shaped belly terminating in a long tendon.

_Relations._—Externally, with the skin; by its tendon, with the border
of the extensor metacarpi radialis longior.

_Action._—Tenses the soft part in the fold of the wing, and aids in
flexing the forearm.

=Tensor Patagii Brevis= (Fig. 14, No. 3). _Location._—In the triangular
patagium of the wing.

_Origin._—From the head of the clavicle in common with the preceding.

_Insertion._—The tendon bifurcates, one branch blending with the fascia
of the extensor metacarpi radialis longior, the other inserting just
below the tubercle on the external condyle of the humerus.

_Shape._—Fleshy; somewhat broader and longer than the preceding.

_Relations._—Interiorly, with the preceding.

_Action._—Assists the tensor patagii longus in flexing the forearm.


                          THE PECTORAL MUSCLES

                          Pectoralis major
                          Pectoralis secundus
                          Pectoralis tertius

=Pectoralis Major= (Fig. 13, No. 5). _Location._—On the lateral side of
the sternum.

_Origin._—From the posterior portion of the lateral wing of the sternal
body, from the outer marginal third of the keel of the sternum, and from
the entire outer side of the limb of the furcula or clavicle.

_Insertion._—The fibers converging form toward the proximal third of the
humerus a broad tendon which by its insertion covers the entire palmar
part of the pectoral crest. A few of the tendinous fibers pass over the
shoulder-joint and blend with the long head of the biceps. Near this
point it receives the insertion of the dermo-humeralis.

_Relations._—Interiorly, with the skin; superiorly, in the sternal
region, with the pectoralis secundus and the pectoralis tertius.

_Shape._—Fleshy; largest of the pectorales.

_Action._—Powerfully depresses the humerus. The chief muscle of flight.

=Pectoralis Secundus= (Fig. 13, No. 9; Fig. 15, No. _A_, 6).
_Location._—The entire lateral side of the sternum.

_Origin._—From the anterior sternal extremity of the lower third of the
coracoid, from the keel and sternal wing, and by a tendon from a
membraneous expansion between the coracoid and the clavicular bones and
from the lower third of the coracoid.

_Insertion._—The fibers converge into a tendon, which passes upward
around the coracoid to its posterior through a canal formed by the
scapula, the coracoid, and the clavicle, the foramen triosseum (Fig. 15,
No. _A_, 7). This tendon then passes outward and downward, and becoming
flat, inserts to the humerus just anterior to the radial crest and
nearer to the humeral head than does the pectoralis major.

_Relations._—Internally, with the breast-bone; externally, with the
pectoralis major; and superiorly, with the pectoralis tertius.

_Shape._—Long, fusiform, fleshy.

_Action._—Raises the wing.

=Pectoralis Tertius= (Fig. 13, No. 6; Fig. 15, No. _A_, 5).
_Location._—On the antero-lateral side of the sternum.

_Origin._—From the anterior half of the exterior of the body of the
sternum, from the fascia of the subclavius on the outer border of the
costal process, and from the outer, lower third of the coracoid process.

_Insertion._—The fibers pass upward to the outer side of the coracoid,
and becoming tendinous as they reach the humerus, by a strong flattened
tendon insert to the ulnar crest of the humerus on the proximal margin
at about a middle point of the pneumatic fossa.

_Relations._—Externally, with the pectoralis major; interiorly, with the
pectoralis secundus; internally, with the fascia of the subclavius and
the sternum.

_Shape._—Fleshy, fusiform.

_Action._—Assists the pectoralis secundus in elevating the humerus.


                     MUSCLES OF THE SCAPULAR REGION

                           Coraco-humeralis
                           Scapulo-humeralis
                           Supraspinatus
                           Subclavius
                           Coraco-brachialis
                           Teres minor
                           Levator scapulæ
                           Thoraco-scapularis
                           Subscapularis

=Coraco-humeralis.= _Location._—The scapulo-humeral region.

_Origin._—From the outer side of the head of the coracoid,
supero-laterally to the long head of the biceps.

_Insertion._—To the palmar part of the head of the humerus just inside
of the insertion of the pectoralis major.

_Shape._—A delicate subcylindrical muscle.

_Relations._—Superior to the head of the humerus.

_Action._—Aids in extending the humerus.

=Scapulo-humeralis= (Fig. 14, No. 10). _Location._—The scapulo-humeral
region.

_Origin._—From the inner side of the neck of the scapula just within the
head of the deltoid.

_Insertion._—Passing over the top of the shoulder-joint it is inserted
to the palmar part of the humeral head between the insertion of the
pectoralis major and the pectoralis secundus.

_Shape._—Narrow, flat ribbon.

_Relations._—Along the upper margin of the larger portion of the
deltoid.

_Action._—Aids in extending the humerus.

=Supraspinatus= (Fig. 19, No. 22). _Location._—Scapular region.

_Origin._—From the superior surface and outer third of the scapula.

_Insertion._—To the lower border of the pneumatic fossa of the humerus.

_Shape._—Thin, flat, triangular.

_Relations._—Externally, with the trapezius and posteriorly, with the
teres et infraspinatus.

_Action._—If the scapula is the fixed point it will pull the humerus
upward and backward.

=Subclavius.= _Location._—Anterior sternal region.

_Origin._—From the entire outer surface of the sternal process of the
sternum and the adjacent outer surfaces of three or four of the
hemapophyses.

_Insertion._—To the inferior margin of the coracoid bone, the longer
fibers passing over to the fossa in the lower third of the posterior
part of the coracoid.

_Shape._—Rather small, fleshy.

_Relations._—Overlapped by the pectoralis tertius.

_Action._—Pulls the coracoid outward. Also aids in keeping the coracoid
in place.

=Coraco-brachialis= (Fig. 13, No. 15). _Location._—Along the coracoid
shaft.

_Origin._—By a delicate tendon from a small circular point on the
postero-mesial part of the shaft of the coracoid immediately above the
attachment of the subclavius and the fossa at that point.

_Insertion._—To the top of the ulnar tuberosity of the humerus. This
subcircular space is common to the teres minor and to this muscle.

_Shape._—Long, fusiform.

_Relations._—With the shaft of the coracoid between the teres minor and
subscapularis.

_Action._—To depress the wing.

=Teres Minor= (Fig. 13, No. 14). _Location._—The coraco-scapular region.

_Origin._—From under the side of the anterior tip of the scapula.

_Insertion._—Passing outward behind the coracoid head and beneath the
neck of the scapula, it is attached by a small tendon to the top of the
ulnar tuberosity of the humerus in common with the coraco-brachialis,
with which tendon it fuses.

_Shape._—Small, chunky.

_Relations._—Anteriorly, with the tip of the scapula and behind the
coracoid head. Posteriorly, with the coraco-brachialis.

_Action._—Aids in the downward stroke of the wing.

=Levator Scapulæ.= _Location._—Scapular region.

_Origin._—By two strong digitations, one from each of the lateral
processes of the first cervical vertebra.

_Insertion._—To the middle third of the inferior part of the blade of
the scapula.

_Shape._—Small and flat.

_Relations._—Inferior to the scapula.

_Action._—Pulls the scapula forward, and with it the entire shoulder
girdle, which articulates like a hinge-joint at the costo-sternal
juncture.

=Thoraco-scapularis.= _Location._—Lateral side of the chest.

_Origin._—From the outer part of the lower half of the first free rib,
the outer side of the next succeeding rib and its epineural appendage,
and from a similar surface on the next rib.

_Insertion._—By a broad, flat tendon which passes between the two
divisions of the subscapularis and inserts at a point at the juncture of
the anterior and middle third of the outer margin of the scapula.

_Shape._—Broad, flat.

_Relations._—Internally, with the ribs and the scapula.

_Action._—When the scapula is fixed it is a muscle of inspiration. When
the ribs are fixed, it draws the scapula downward.

=Subscapularis.= _Location._—Scapulo-humeral region.

_Origin._—From the anterior and outer half of the scapula.

_Insertion._—By a strong and subcylindrical tendon to the top of the
ulnar tuberosity of the humerus close to the combined tendons of the
coraco-brachialis and teres minor.

_Shape._—A large and powerful muscle.

_Relations._—The flat tendon of the thoraco-scapularis divides the
posterior portion of the belly into two portions.

_Action._—A powerful rotary muscle of the head of the humerus; aids in
keeping the humeral head in the glenoid cavity.


                   THE MUSCLES OF THE BRACHIAL REGION

                           Biceps
                           Triceps
                           Deltoid
                           Brachialis anticus

=Biceps= (Fig. 13, No. 8). (Synonym.—Biceps brachii.)

_Location._—The anterior brachial region.

_Origin._—By a broad tendon it covers the top of the shoulder-joint,
dividing into two heads, giving rise to the long and the short heads.
The long is inserted into the outer part of the head of the coracoid
just beyond the glenoid cavity; the short head to the distal angle of
the ulnar tuberosity of the humerus.

_Insertion._—To the ulna just in front of the articular cavity for the
trochlear surface of the distal extremity of the humerus.

_Shape._—Large, subfusiform.

_Relations._—On one side by the triceps and the other the deltoid and
anteriorly partially covered by the patagii muscles.

_Action._—A powerful flexor of the forearm.

=Deltoid= (Fig. 13, No. 12; Fig. 15, No. 8). _Location._—Occupying the
lateral side of the humerus; the brachial region.

_Origin._—Divided into two portions, the long narrow head extends from
the clavicular process of the scapula and from the adjacent surface of
the same bone. These fibers then extend around the back of the
shoulder-joint, and are joined by the fibers that arise from the entire
outer surface of the large os humero-scapulare. These latter fibers are
inserted upon an extensive area upon the anconal part of the bone beyond
the humeral articular head, and to almost the entire shaft below it.

_Insertion._—By a subcylindrical tendon to the proximal side of the
tubercle of the external condyle, and above the insertion of the
extensor metacarpi radialis longus.

_Shape._—Large, fleshy, with tendinous attachment.

_Relations._—On one side by the biceps and the other by the triceps also
the patagii.

_Action._—To extend the arm.

=Triceps= (Fig. 15, No. 7). (Synonym.—Triceps brachii.)

_Location._—The posterior humeral region.

_Origin._—By three portions: by the internal and external heads, and by
the long scapular head. The internal and the external heads are blended
except at their proximal extremities. Each head arises from the anconal
surface of the shaft of the humerus. The internal head being located
toward the deltoid attachment and the external head into the pneumatic
fossa. The long head extends from a circumscribed area just posterior to
the glenoid cavity of the scapula. The fibers pass around the
shoulder-joint, beneath the deltoid.

_Insertion._—The broad tendon passes over the elbow-joint and is
inserted to the entire under surface of the olecranon of the ulna.

_Shape._—Long, large, fleshy.

_Relations._—The supraspinatus passes between the internal and the
external heads. It is bounded by the biceps and the deltoid.

_Action._—An extensor of the antibrachial region directly antagonizing
the biceps.

=Brachialis Anticus= (Fig. 15, No. 9; Fig. 14, No. 5). _Location._—In
the flexure of the humerus and the ulna.

_Origin._—It arises fleshy from a circumscribed area on the inner side
of the anconal part of the distal extremity of the humerus.

_Insertion._—The fibers passing directly over the elbow-joint become
inserted to the lateral surface of the proximal end of the ulna close to
the margin of the sigmoid cavity.

_Shape._—Small, fleshy.

_Relations._—With the joint.

_Action._—Assists in flexing the forearm upon the arm. Protects the
structures in the anterior part of the elbow-joint.


                THE MUSCLES OF THE FOREARM AND THE HAND

                  Extensor metacarpi radialis longior
                  Supinator brevis
                  Extensor digitorum communis
                  Pronator brevis
                  Flexor metacarpi radialis
                  Extensor ossis metacarpi pollicis
                  Pronator longus
                  Extensor indicis longus
                  Flexor digitorum sublimis
                  Flexor digitorum profundus
                  Flexor carpi ulnaris
                  Flexor carpi ulnaris brevior

=Extensor Metacarpi Radialis Longior= (Fig. 13, No. 17).
_Location._—Superior to the radius.

_Origin._—By two strong tendinous heads; the outer from the tubercle of
the external condyle of the humerus, just above the origin of the tendon
of the tensor patagii brevis; the inner and stronger portion from the
tubercle found above the oblique trochlear facet of the distal end of
the radius.

_Insertion._—Becoming a flat, broad, and strong tendon at about the
middle of the forearm, finally becomes inserted to the apex of the
anchylosed first metacarpal of the carpo-metacarpus.

_Shape._—A thick, fusiform belly, tendinous at both extremities.

_Relations._—By the side of the pronator brevis.

_Action._—Raises the hand, and draws it forward toward the radial margin
of the forearm and retains it on the same side.

=Extensor Digitorum Communis= (Fig. 15, No. 2). _Location._—The upper
metacarpal region.

_Origin._—Immediately below the tubercle of the external condyle of the
humerus.

_Insertion._—By a small tendon to the outer side of the base of the
pollex, and at a mid-point upon the anterior rim of the proximal phalanx
of the middle finger.

_Shape._—Small spindle-shaped, becoming tendinous at about the middle of
the forearm.

_Relations._—Occupies the middle of the group of muscles on the outer
side of the forearm.

_Action._—An extensor of the digit.

=Supinator Brevis= (Fig. 14, No. 7). _Location._—The superior part of
the radius.

_Origin._—From the external condyle of the humerus below the origin of
the tendon of the extensor digitorum communis.

_Insertion._—To the outer side of the shaft of the radius, for nearly
one-third of its length.

_Shape._—Thin, slender.

_Relations._—Inferiorly, with the bone.

_Action._—A supinator of the radial region, and antagonistic to the
pronators.

=Flexor Metacarpi Radialis= (Fig. 15, No. 10). _Location._—The lowest of
the group of three muscles on the outer part of the forearm.

_Origin._—By two tendinous heads, the longer from the external condyle
of the humerus, and the other just beyond the base of the olecranon.

_Insertion._—Becomes tendinous at about the middle of the shaft of the
ulna and inserts to a prominent process on the proximal third of the
posterior part of the shaft of the mid-metacarpal.

_Shape._—Fusiform.

_Relations._—Inferiorly, the anconeus and superiorly, the extensor
digitorum communis.

_Action._—A powerful flexor of the hand.

=Pronator Brevis= (Fig. 13, No. 18). _Location._—Supero-lateral side of
the forearm.

_Origin._—From just above the internal condyle of the humerus.

_Insertion._—The tendon passing obliquely across the interosseous space
and is inserted to the ulnar side of the shaft of the radius, just
beyond the juncture of the proximal and the middle thirds.

_Shape._—Fusiform.

_Relations._—Superior to the pronator longus.

_Action._—Pronates the forearm, and flexes the forearm upon the arm.

=Pronator Longus= (Fig. 14, No. 6). _Location._—Lateral side of the
radio-ulnar region.

_Origin._—From the middle of the internal condyle of the humerus.

_Insertion._—To the shaft of the radius just beneath the pronator
brevis.

_Shape._—Massive, ellipsoidal.

_Relations._—Between the pronator brevis and flexor digitorum profundus.

_Action._—A pronator.

=Extensor Ossis Metacarpi Pollicis= (Fig. 13, No. 23).
_Location._—Slightly interposed between the ulna and radius.

_Origin._—Immediately in front of the greater sigmoid cavity of the
ulna.

_Insertion._—To the palmar side of the base of the first metacarpal, in
common with the extensor metacarpi radialis longior.

_Shape._—Delicate, straight.

_Relations._—Superiorly, the extensor indicis longus, and inferiorly,
the anconeus and the flexor digitorum profundus.

_Action._—Extends the hand upon the forearm.

=Anconeus= (Fig. 15, No. 4). _Location._—Between the ulna and the
radius.

_Origin._—By a short, strong, subcylindrical tendon from the lower
posterior of the external condyle of the humerus.

_Insertion._—To the latero-radial side of the ulna somewhat beyond its
middle.

_Shape._—Fusiform.

_Relations._—Superiorly, the extensor indicis longus, and inferiorly,
the ulna.

_Action._—A flexor of the forearm.

=Extensor Indicis Longus= (Fig. 13, No. 22; Fig. 15, No. 13).
_Location._—Infero-lateral to the radius.

_Origin._—From about one-half the surface of the proximal portion of the
radius.

_Insertion._—Possesses a long tendon which passing over a groove at the
distal end of the ulna and receiving muscular fibers at the base of the
metacarpus, extends down the anterior part of the hand and is inclosed
in a sheath in front of the superior part of the first phalanx of the
index-finger. This tendon is inserted into the anterior upper rim of the
distal phalanx.

_Shape._—Small, thin.

_Relations._—Supero-laterally with the radius.

_Action._—Extensor of the digit.

=Flexor Digitorum Sublimis.= _Location._—The forearm.

_Origin._—From the internal condyle of the humerus.

_Insertion._—Passing over the wrist, it is inserted to the middle
phalanx of the hand.

_Shape._—A musculo-tendinous band, rather delicate and rudimentary.

_Relations._—Closely adhering to the integument that stretches from the
internal condyle of the humerus to the wrist.

_Action._—Assists these muscles. A flexor.

=Flexor Digitorum Profundus= (Fig. 13, No. 21). _Location._—Lateral side
of the ulna.

_Origin._—By two heads from the proximal extremity of the ulna, between
which the brachialis anticus passes.

_Insertion._—The two bellies uniting are attached to the under side of
the shaft of the ulna. It becomes tendinous about the middle of the
shaft, and inserts to the ulnar side of the base of the distal joint of
the index-finger.

_Shape._—A fleshy belly with long tendon.

_Relations._—Inferiorly, with the flexor carpi ulnaris, superiorly, with
the pronator brevis.

_Action._—A flexor of the digit.

=Flexor Carpi Ulnaris= (Fig. 13, No. 19). _Location._—Inferior part of
the forearm.

_Origin._—By two strong tendons; one from the side and posterior of the
internal condyle of the humerus, passing through the humero-ulnar pulley
at the side of the base of the olecranon process; the other, to the
posterior of the internal condyle of the humerus. It does not pass
through a pulley.

_Insertion._—A subcylindrical tendon extends back of the ulnare ossicle
of the carpus giving off a tendinous slip to the flexor digitorum
profundus, and becomes inserted to the anterior rim of the proximal
phalanx of the index digit. It has an attachment at the carpus.

_Shape._—A strong fleshy belly terminating in a long tendon.

_Relations._—The outermost inferior muscle of the forearm.

_Action._—A powerful flexor of the hand upon the forearm.

=Flexor Carpi Ulnaris Brevior= (Fig. 13, No. 20). _Location._—Inferior
part of the antibrachial region.

_Origin._—From a broad area on the middle third of the upper side of the
shaft of the ulna.

_Insertion._—Near the top of the outer edge of the anchylosed os magnum
of the carpo-metacarpus.

_Shape._—Thin, somewhat flat.

_Relations._—To the inside of the flexor digitorum profundus.

_Action._—Flexes the hand upon the forearm and rotates the hand toward
the body.


                      OTHER MUSCLES OF THE DIGITS

                      Extensor proprius pollicis
                      Flexor minimi digiti
                      Abductor minimi digiti
                      Interosseous palmaris
                      Flexor brevis pollicis
                      Flexor minimi digiti brevis
                      Interosseous dorsalis
                      Flexor metacarpi brevis

=Extensor Proprius Pollicis= (Fig. 13, No. 29a). _Location._—Anterior to
the radio-carpal joint.

_Origin._—From the ulnar side of the tendon of the extensor metacarpi
radialis longior.

_Insertion._—To the antero-ulnar side of the pollex.

_Shape._—Small, spindle-shaped; tendinous at both attachments.

_Relations._—Inferiorly, with the proximal and anterior part of the
metacarpus.

_Action._—An extensor of the pollex.

=Flexor Brevis Pollicis= (Fig. 13, No. 28a). _Location._—Anterior to the
pollex.

_Origin._—From the shaft of the mid-metacarpal bone, just below the
pollex.

_Insertion._—Distal apex of the pollex.

_Shape._—Short, small, fleshy.

_Relations._—Superiorly, with the inferior part of the pollex.

_Action._—Flexes the pollex.

=Flexor Minimi Digiti.= _Location._—Inferior side of the metacarpus.

_Origin._—From the posterior part of the median metacarpal close to the
os carpi ulnare. A few fibers extend to the ulna.

_Insertion._—Into the base of the median phalanx.

_Shape._—Small, slender, short.

_Relations._—Superiorly, with the metacarpal bone.

_Action._—A flexor of the digit.

=Flexor Minimi Digiti Brevis= (Fig. 13, No. 30). _Location._—Inferior to
the third, or small finger.

_Origin._—From the lower and posterior end of the median metacarpal and
from the adjacent tendon of the preceding.

_Insertion._—Inserted to the apex of the small finger.

_Shape._—Small and rather rudimentary.

_Relations._—Inferior to the small finger.

_Action._—Acts as a posterior ligament of this joint.

=Abductor Minimi Digiti.= _Location._—Supero-lateral side of the small
finger.

_Origin._—From the proximal extremity of the anterior aspect of the
third finger.

_Insertion._—To the posterior border of the proximal phalanx of the
second, or index-finger at a point just above the tip of the third
finger.

_Shape._—A few muscular fibers with some tendinous material.

_Relations._—At the base of the median segment of the index-finger and
to the side of the third.

_Action._—Antagonizes the powerful flexors on the back of the joint.

=Interosseus Dorsalis= (Fig. 13, No. 31). _Location._—By the side of the
metacarpus.

_Origin._—From the margin of the shaft of the median metacarpal.

_Insertion._—To the anterior part of the base of the distal phalanx of
the index digit.

_Shape._—Short, delicate, with long tendon.

_Relations._—Internally, the metacarpal bone.

_Action._—Extends the last bone of the middle finger.

=Interosseus Palmaris= (Fig. 13, No. 32). _Location._—On the opposite
side of the bone from the interosseous dorsalis.

_Origin._—From the shaft of the median metacarpal under the preceding.

_Insertion._—To the apex of the last joint of the second, or middle
finger.

_Shape._—Small, delicate, with long slender tendon.

_Relations._—Beneath the preceding and along the metacarpal bone.

_Action._—Flexes the terminal phalanx.

=Flexor Metacarpi Brevis.= _Location._—To the lateral side of the
metacarpal bone.

_Origin._—From the outer side of the distal extremity of the ulna.

_Insertion._—To the base, in front, and on the ulnar side of the
proximal phalanx of the index digit.

_Shape._—Delicate, with long slender tendon.

_Relations._—On the lateral side of the ulna and the metacarpal bone.

_Action._—Flexes the metacarpus.


                     MUSCLES OF THE POSTERIOR LIMB

                       Sartorius
                       Gluteus medius
                       Extensor femoris
                       Biceps flexor cruris
                       Semitendinosus accessorius
                       Femoro-caudal
                       Obturator internus
                       Abductor longus
                       Gluteus primus
                       Gluteus minimus
                       Vastus internus
                       Semitendinosus
                       Semimembranosus
                       Obturator externus
                       Gemellus
                       Adductor magnus

=Sartorius= (Fig. 23, No. 7). _Location._—Extreme anterior portion of
the thigh.

_Origin._—From the outer two-thirds of the superior surface of the
raised emarginations of the anterior border of the ilium, and by fascia
from the neural spines of the fourth dorsal vertebra.

_Insertion._—Obliquely by a semitendinous fascia to the inner edge of
the ligamentum patella, and to the inner and adjacent border of the
anterior half of the summit of the tibia.

_Shape._—Large, fleshy.

_Relations._—Posteriorly, with the gluteus primus and the vasti.

_Action._—Extends the leg, flexes and adducts the thigh.

=Gluteus Primus= (Fig. 23, No. 8 and 9). _Location._—The outer flat
massive muscle of the thigh.

_Origin._—By a thin fascia from nearly the entire length of the
supero-internal margin of the pre-acetabular portion of the ilium, above
the antitrochanter, and from the entire length of the post-acetabular
ridge.

_Insertion._—Near the patella it joins the tendon of the extensor
femoris, and by aponeurosis spreads over the knee and is inserted to the
crest of the upper border of the tibia, the patella being incorporated
in its aponeurotic ligament.

_Shape._—Triangular in shape, it is aponeurotic anteriorly and more
fleshy posteriorly.

_Relations._—Anteriorly, covers over the posterior portion of the
sartorius and the body of the gluteus medius; posteriorly, bordered by
the semitendinosus and the biceps.

_Action._—Abducts the thigh.

=Gluteus Medius= (Fig. 24, No. 11). _Location._—Supero-anterior part of
the ilium under the gluteus primus.

_Origin._—From the entire supero-internal margin of the pre-acetabular
surface of the ilium and the concave surface on the adjacent bone.

_Insertion._—By a strong tendon which passes over a bursa on the
anterior rim of the trochanter and is inserted obliquely to this
trochanter.

_Shape._—A fleshy muscle filling the concavity of the pre-acetabular
division of the ilium.

_Relations._—Superiorly, with the gluteus primus; inferiorly, with the
gluteus minimus.

_Action._—Abducts and pulls the femur forward.

=Gluteus Minimus= (Fig. 24, No. 12). (Synonym.—Gluteus profundus.)

_Location._—Beneath the medius and the smaller of the two.

_Origin._—To the anterior margin of the outer border of the ilium, and
from the supero-external surface of the last rib.

_Insertion._—The fibers extending downward and backward and outward
become tendinous and are inserted below the trochanter of the outer part
of the upper third of the femur.

_Shape._—Small, fleshy.

_Relations._—Inferiorly, with the bone and superiorly, with the gluteus
medius.

_Action._—Abducts and pulls the thigh forward.

=Extensor Femoris= (Fig. 24, No. 15). _Location._—Anterior femoral
region. It is divided into two parts: the vastus externus and the
crureus.

_Origin._—The vastus extemus (Fig. 24, No. 14) arises tendinous from the
base of the trochanter of the outer part of the femur and from this
point down the bone approximately to the condyle. The crureus (Fig. 24,
No. 13) originates by a tendon from the anterior upper prominent rim of
the trochanter, from this point extending down the antero-external part
of the shaft of the femur.

_Insertion._—Merges with the gluteus primus, and, by a fascia-like
arrangement, spreads over the front of the knee-joint inserts to the
patella and is also inserted into the crest of the tibia.

_Shape._—Large, fleshy.

_Relations._—Posteriorly, with the femur and anteriorly, with the
sartorius.

_Action._—Extends strongly the leg upon the thigh.

=Vastus Internus= (Fig. 16, No. 3). _Location._—Internal and lateral
side of the femur.

_Origin._—From the postero-internal part of the shaft of the femur just
below the head, and in a straight line extending down the femur.

_Insertion._—By a broad tendon along the thickened inner border of the
summit of the tibia.

_Shape._—Thick, long.

_Relations._—Anteriorly, with the bone; surrounded by the other crural
muscles.

_Action._—Extends the leg upon the knee; a powerful assistant of the
extensor femoris.

=Biceps Flexor Cruris= (Fig. 17, No. D, 1). _Location._—Posterior tibial
region.

_Origin._—By a tendinous fascia from the post-acetabular ridge,
extending between the antitrochanter and the anterior point of the
insertion of the semitendinosus.

_Insertion._—To the tuberosity on the external part of the shaft of the
fibula a short distance below the head.

_Shape._—Large, rather cone-shaped with base directed upward.

_Relations._—Anteriorly, with the vastus externus; posteriorly, with the
semitendinosus. The inferior tendinous portion passes through a
tendinous sling or pulley called the biceps band.

_Action._—Flexes the leg upon the thigh.

=Semitendinosus= (Fig. 23, No. 10). _Location._—Posterior femoral
region.

_Origin._—By a tough, strong fascia from the surface of the caudal
muscles and from the posterior third of the post-acetabular ridge.

_Insertion._—The fibers pass downward and forward, and insert to the
tendinous raphe along the posterior margin of the semitendinosus
accessorius; lower down it merges with the median fascia of the inner
head of the gastrocnemius.

_Shape._—Fleshy, broad, flat and long.

_Relations._—Internally, with the semimembranosus and anteriorly, with
the biceps flexor cruris.

_Action._—Flexes the leg.

=Semitendinosus Accessorius.= _Location._—Posterior femoral region.

_Origin._—From an oblique line just above the condyle, on the posterior
of the shaft of the femur.

_Insertion._—Its fibers, passing upward and backward, attach themselves
to the tendinous raphe common to this muscle and the semitendinosus, and
are finally inserted to the inner side of the shaft of the tibia.

_Shape._—Flat, oblong.

_Relations._—Posteriorly to the shaft of the femur, and externally to
the long adductors of the thigh.

_Action._—Aids the preceding in flexing the leg.

=Semimembranosus= (Fig. 24, No. 17). _Location._—Postero-internal to the
semitendinosus.

_Origin._—From the outer surface of the ischium, beginning at the lower
margin of its notch on the posterior pelvic border, extends on a curved
line on the adjacent surface beyond.

_Insertion._—The fibers, passing downward and forward, insert by a
broad, thin tendon to the shaft of the tibia a short distance below the
head and on a line parallel to the long axis of the tibia.

_Shape._—Long, narrow, ribbon-shaped.

_Relations._—Lies adjacent to the semitendinosus and in the same plane.

_Action._—Directly flexes the leg.

=Femoro-caudal= (Fig. 24, No. 8). _Location._—Infero-lateral to the
caudal and post-femoral region.

_Origin._—By a delicate tendon from the base of the pygostyle.

_Insertion._—By a thin, flat tendon upon the outer part of the shaft of
the femur below the trochanter and at about the juncture of the upper
and middle third of the bone.

[Illustration:

  FIG. 24.—Second layer of muscles of the thigh of a cock. Outside view.
    1, Appendico-costales. 2, Levatores costarum. 3, Sacro-lumbalis. 4,
    Longissimus dorsi. 5, Intercostales. 6, Longissimus dorsi. 7,
    Latissimus dorsi. 8, Femoro-caudal. 9, Edge of obturator externus.
    11, Gluteus medius. 12, Gluteus minimus. 13, Crureus. 14, Vastus
    externus. 15, Extensor femoris. 16, Biceps flexor cruris. 17,
    Semimembranosus. 18, Adductor magnus. 19, Adductor longus. 20,
    External abdominal oblique. 21, Depressor coccygis. 22, Tibialis
    anticus. 23, Tibialis posticus. 24, Flexor perforans digitorum
    profundus. 25, Flexor perforatus medius secundus pedis. 26, Flexor
    longus hallucis.
]

_Shape._—Long, narrow, spindle-shaped, flattened from side to side.

_Relations._—Interiorly to the obturator externus, and along the upper
border of the long adductors of the thigh and the semimembranosus.

_Action._—Pulls the tail down and to one side.

=Obturator Externus= (Fig. 24, No. 9). _Location._—External
posterolateral side of the pelvis.

_Origin._—From the posterior half of the periphery of the ischiatic
foramen and the concavity found on the external surface of the lateral
part of the pelvis.

_Insertion._—The fibers pass across to the femur and are inserted by a
broad, flat tendon to the shaft of the femur just below the trochanter.

_Shape._—Thick, fleshy.

_Relations._—Lies just above the femoro-caudal muscle, the sciatic nerve
and femoral artery pass over and external to its tendon.

_Action._—Pulls the head of the femur backward.

=Obturator Internus= (Fig. 16, No. _E_, 1). _Location._—Occupies the
space between the ischium and the pubis.

_Origin._—From the ventral surface of the ischium, including the
posterior border, from the inner line of the corresponding post-pubis,
and from the membrane covering the space between these two bones.

_Insertion._—Becoming dense, subcylindrical, and strong, it passes
through the obturator foramen and is inserted to the outer part of the
trochanter of the femur, in common with the gemellus and opposite to the
insertion of the gluteus medius.

_Shape._—Subtriangular and flat with a central tendon; bipenniform.

_Relations._—Outside the pelvis the tendon lies upon the gemellus and is
external to it. Fills the obturator foramen and the space between the
ischium and the pubis.

_Action._—Acts as a posterior stay to the head of the femur.

=Gemellus= (Fig. 25, No. 5). _Location._—Posterior to the head of the
femur.

_Origin._—From the fossa between the acetabulum and the obturator
foramen, and on the outer side of the pelvis.

_Insertion._—Its fibers are attached by fascia to the tendon of the
obturator internus, and pass directly to the trochanter of the femur
where they insert in common with that of the obturator internus.

_Shape._—Strong, thick, chunky.

_Relations._—Postero-external to the head of the femur.

_Action._—Like the two preceding, when the head of the femur is fixed,
it pulls the pelvis forward and steadies it on the head of the femur.

=Adductor Longus= (Fig. 24, No. 19). _Location._—In the posterior
femoral region.

_Origin._—From a line on the lateral part of the pelvis.

_Insertion._—The fibers, passing downward and forward, are inserted on a
longitudinal line along the posterior part of the shaft of the femur.

_Shape._—Broad, flat, fleshy.

_Relations._—Posteriorly to the femur, and anteriorly to the adductor
magnus.

_Action._—Adducts the thigh.

=Adductor Magnus= (Fig. 24, No. 18). _Location._—Posterior femoral
region.

_Origin._—From the fine constituting the lower boundary of the ischiatic
fossa on the outer lateral part of the pelvis.

_Insertion._—The fibers pass downward and are inserted to the superior
curve of the internal femoral condyle. The internal head of the
gastrocnemius blends with this muscle just above its attachment.

_Shape._—Long, narrow.

_Relations._—Posteriorly to the adductor magnus and anteriorly to the
semimembranosus.

_Action._—Strongly adducts the thigh.


                            THE TIBIAL GROUP

                Gastrocnemius
                Peroneus longus
                Extensor longus digitorum
                Tibialis posticus
                Flexor longus hallucis
                Flexor perforatus annularis primus pedis
                Flexor perforatus medius secundus pedis
                Flexor perforans digitorum profundus
                Soleus
                Tibialis anticus
                Extensor hallucis brevis
                Flexor perforatus indicis secundus pedis
                Flexor perforatus medius primus pedis
                Flexor perforatus indicis primus pedis
                Extensor brevis digitorum
                Flexor hallucis brevis
                Extensor annularis brevis

=Gastrocnemius= (Fig. 23, No. 11). _Location._—Posterior tibial region.

_Origin._—There are three heads: the internal, the external, and the
tibial. The external head extends by a short, flattened, strong tendon
from the postero-external part of the external condyle of the femur; the
internal head extends from the outer surface of the inner condyle of the
femur; and the tibial head extends from the entire inner rim of the
tibial summit and from the free edge of the adjacent crest.

_Insertion._—At the lower fourth of the tibial shaft, terminates in a
broad, flat tendon which passes over the shallow, longitudinal groove of
the tibial cartilage, and, crossing the tibio-tarsal joint, is inserted
to the posterior surface of the hypotarsus of the metatarsal bone, and
finally, below this point, merges into the podothecal sheath confining
the flexor tendons.

_Shape._—Large, fleshy, somewhat cone-shaped with the base upward.

_Relations._—The posterior fleshy muscle of the post-tibial region
located anterior to the soleus.

_Action._—Extends the metatarsus on the tibia.

=Soleus= (Fig. 25, No. _G_, 1). _Location._—The posterior tibial region.

_Origin._—From the posterior part of the head of the tibia.

_Insertion._—By a long slender tendon to the proximal end and toward the
inner angle of the tibial cartilage, some of the fibers passing to the
tendon of the gastrocnemius.

_Shape._—Small, flattened.

_Relations._—Anteriorly, with the flexor perforans digitorum profundus
and posteriorly, with the gastrocnemius.

_Action._—Similar to that of the gastrocnemius.

=Peroneus Longus= (Fig. 23, No. 12). _Location._—Antero-lateral tibial
region.

_Origin._—From the raised crest in front of the head of the tibia, and
from the fascia that covers the outer side of the knee-joint.

_Insertion._—The fibers, passing downward, then downward and outward,
terminate in a small tendon at the lower third of the tibia. This tendon
bifurcates just above the tibial condyles at the outer part of the limb,
the shorter and stronger attaches to the fibrous fascia covering the
tibial cartilage, the other merging with the tendon of the flexor
perforatus medius primus pedis about 1 centimeter below the hypotarsus
of the tarso-metatarsus.

_Relations._—Covers over all the muscles of the anterior tibial region.

_Shape._—A broad muscular sheet.

_Action._—Assists the flexor perforatus medius primus pedis.

=Tibialis Anticus= (Fig. 24, No. 22). _Location._—In the anterior tibial
region.

_Origin._—The muscular belly may be easily divided into two parts. The
inner head extends from the head of the tibia immediately beneath the
peroneus longus. The outer head arises by a strong tendon from a
depression on the antero-inferior ridge of the outer condyle of the
femur.

_Insertion._—The tendon passing through the fibrous ligamentous loop
just above the tibial condyles, inserts to a tubercle on the shaft just
below the head of the tarso-metatarsus.

_Shape._—Large, fusiform.

_Relations._—Beneath the peroneus longus.

_Action._—Flexes the metatarsus upon the tibia.

=Extensor Longus Digitorum= (Fig. 25, No. _G_, 6). _Location._—Anterior
tibial region.

_Origin._—From the inferior portion of the crest and a portion of the
shaft of the fibula.

_Insertion._—It becomes tendinous at the lower third of the bone,
passing under the bony ridge just above the condyle in front, and over
the ankle-joint. It is bound down by firm fascia, and at the trochlea of
the basal toe joints, divides into three small tendinous slips. These
pass over the superior part of the second, the third, and the fourth
toes, bifurcating in their course, and are inserted to the distal ones.

_Shape._—Long, penniform, with a long, slender tendon.

_Relations._—Immediately below the tibialis anticus.

_Action._—Extends the digits as their long extensor.

=Extensor Hallucis Brevis= (Fig. 25, No. _G_, 4). _Location._—The
anterior metatarsal region, along the antero-internal edge.

_Origin._—From just below the summit of the antero-internal part of the
head of the tarso-metatarsus, and from the adjacent shaft below, and
from the tendon of the tibialis anticus.

_Insertion._—Into the process at the superior part of the bone of the
bony claw of the hallux.

_Shape._—Slender, thin in diameter, with a long, slender tendon.

_Relations._—Superiorly, with the antero-internal edge of the metatarsus
and interiorly, its tendon with the top of the hallux.

_Action._—Extends the hallux.

=Extensor Brevis Digitorum.= _Location._—On the anterior surface of the
metatarsus.

[Illustration:

  FIG. 25.—Inner layer of muscles of the thigh of a hen. Outside view.

  _A._ Pad of fibrocartilage or meniscus of femoro-tibial articulation.
    1, Inner semi-lunar fibrocartilage. 2, External semi-lunar
    cartilage. 3, Anterior border.

  _B._ Tarsal meniscus or pad of fibrocartilage.

  _C._ Articular surface of the tarsal joint. 1, Posterior ligamentum
    cruciatum genu. 2, Femoral tendinous insertion of tibialis anticus.
    3, Ligamentum tibio-fibulare. 4, Ligamentum interosseum. 5,
    Ligamentum transversum of the meniscus. 6, Anterior ligamentum
    cruciatum genu.

  _D._ 1, Tibia. 2, Fibula. 3, Femur. 4, External ligamentum laterale
    genu.

  _E._ Inferior surface of the tail of a hen. 1, Infracoccygis. 2,
    Lateralis coccygis.

  _F._ Outside pelvic view. 1, Obturator ligament. 2, Tendon of the
    obturator internus. 3, Ligamentum oblongum. 4, Ligamentum capsulare.
    5, Gemellus.

  _G._ Outside view of leg of a cock. 1, Soleus. 2, Flexor longus
    hallucis. 3, Flexor perforans digitorum profundus. 4, Extensor
    brevis hallucis. 5, Extensor brevis annularis. 6, Extensor longus
    digitorum. 7, Tendon of the tibialis posticus.

  _H._ 1, Transversalis abdominalis. 2, Cotyloid cavity.
]

_Origin._—By a small fleshy belly to the anterior part of the proximal
end of the metatarsus.

_Insertion._—It becomes tendinous about the middle third of the
metatarsus. Extending down the anterior face of the metatarsus it is
inserted to the inner tubercle of the base of the first phalanx of the
outer or fourth toe.

_Shape._—Long, slender.

_Relations._—Posteriorly with the metatarsus.

_Action._—Pulls the fourth toe upward and inward.

=Flexor Hallucis Brevis.= _Location._—Postero-internal side of the
metatarsus.

_Origin._—Side and lower margin of the inner aspect of the hypotarsus of
the tarso-metatarsus and from the shaft of this bone immediately below
it.

_Insertion._—Winds round inner side of basal joint of the hallux and is
inserted on its under side.

_Shape._—Small flat muscle gradually tapering into a tendon.

_Relations._—Posteriorly with the metatarsus.

_Action._—To flex the hallux.

=Extensor Annularis Brevis.= _Location._—On postero-external side of
metatarsus.

_Origin._—External aspect of the hypotarsus and the shaft below.

_Insertion._—Supero-external part of the basal phalanx of the fourth
toe.

_Shape._—Small flat muscle.

_Relations._—Posteriorly with the metatarsus.

_Action._—Extensor of the fourth toe.

=Tibialis Posticus= (Fig. 24, No. 23). _Location._—In the posterior
tibial region.

_Origin._—From the whole shaft of the fibula below the insertion of the
biceps flexor cruris, and from the shaft of the tibia a short distance
below this insertion. Also from the interosseous membrane, and the
adjacent surface of the tibial shaft.

_Insertion._—Passing in front of the external malleolus, crossing the
ankle-joint, finally inserted into the outer edge of the summit of the
tarso-metatarsal bone.

_Shape._—Long, subcylindrical.

_Relations._—Medially, with the flexor perforans digitorum pedis;
superiorly, with the postero-external portion of the tibia.

_Action._—Extends the metatarsus upon the tibia.

=Flexor Perforatus Indicis Secundus Pedis= (Fig. 17, No. 5).
_Location._—The posterior tibial region.

_Origin._—From the external surface of the outer condyle of the femur,
just below the head of the gastrocnemius.

_Insertion._—Passing in an oblique manner along posterior to the tibia,
extends through the superficial part of the tibial cartilage to the
outer side of the leg; then crossing the tibio-tarsal joint, it passes
through a special canal of the hypotarsus, down the back of the
tarso-metatarsus, under the annular ligament of the sole of the foot and
a cartilaginous structure below this ligament, over the trochlea, and is
inserted to the middle shaft of the second phalanx of the second toe.

_Shape._—Thin, flat, broadly spindle-shaped.

_Relations._—Posteriorly, with the flexor perforatus medius secundus
pedis, and anteriorly, with the flexor perforatus annularis primus
pedis.

_Action._—Flexes the toes.

=Flexor Longus Hallucis= (Fig. 17, No. 7; Fig. 25, No. 2).
_Location._—The posterior tibial region.

_Origin._—By two tendinous heads: one from the posterior part of the
femur, just below the two condyles; the other from the outer part of the
external condyle of the femur. The deep flexor passes between these two
heads.

_Insertion._—Becoming tendinous at the lower third of the leg, passes
beneath the superficial flexors in a special canal on the outer side of
the tibial cartilage, and extends through the large canal of the
hypotarsus (Fig. 12, No. _F_, 5) next to the shaft, then down to the
apex of the accessory metacarpal bone. It is inserted to the tubercle on
the inferior proximal end of the ungual phalanx.

_Shape._—Large, fusiform.

_Relations._—With the exterior of the deep flexors.

_Action._—Flexes the hallux as its long flexor.

=Flexor Perforatus Annularis Primus Pedis= (Fig. 17, Nos. _D_, 8 and
_C_, 6). _Location._—The posterior tibial region.

_Origin._—From the inner side of the belly of the flexor longus
hallucis.

_Insertion._—Becoming tendinous at the lower third of the tibia, passes
a little to the outer side and through the tibial cartilage, then over
the ankle-joint and through the hypotarsal canal (Fig. 12, No. 5) to the
under side of the outer toe, where it forms a sheath through which the
deep flexors extend. It gives off on either side a tendinous slip which
attaches to the basal phalanx.

_Shape._—Long, slender, compressed laterally.

_Relations._—Internally, with the flexor perforatus indicis secundus
pedis, and externally, with the flexor longus hallucis.

_Action._—Flexes the toes as their long flexor. A second flexor of the
outer toe.

=Flexor Perforatus Medius Secundus Pedis= (Fig. 17, No. 9).
_Location._—The posterior tibial region.

_Origin._—From a strong fascia that merges with the knee-joint, and by a
tendon from the external condyle of the femur in common with the tendon
of the flexor perforatus indicis secundus pedis.

_Insertion._—Continued as a flattened tendon extending from the lower
third of the leg, passing obliquely through the tibial cartilage and
then through the interno-posterior canal of the hypotarsus, (Fig. 12,
No. _F_, 5) inserted to the second joint of the middle toe.

_Shape._—Long, fusiform.

_Relations._—With the shaft of the fibula, which it covers.

_Action._—Flexes the middle toe.

=Flexor Perforatus Medius Primus Pedis= (Fig. 17, No. 2).
_Location._—Posterior tibial region.

_Origin._—From the inner side of the muscular portion of the flexor
perforatus annularis primus pedis.

_Insertion._—Terminating in a flattened tendon, passes through the
tibial cartilage and hypotarsus, and then extends along the shaft of the
basal joint of the third toe, and, dividing into two slips, inserts to
either side of its shaft.

_Shape._—Long, rather small.

_Relations._—With the flexor perforatus annularis primus pedis on the
inner side.

_Action._—Flexes the third toe.

=Flexor Perforatus Indicis Primus Pedis= (Fig. 17, No. 4).
_Location._—The posterior tibial region.

_Origin._—From a thin, broad tendon, on the external condyle of the
femur, in common with the flexor perforatus medius secundus pedis.

_Insertion._—Becoming tendinous, passes through the tibial cartilage and
the hypotarsus of the metatarsus (Fig. 16, _A_) and inserts to the sides
of the basal joint of the second toe.

_Shape._—Long, slender, fusiform; somewhat flattened laterally.

_Relations._—With the flexor perforatus medius secundis pedis,
posteriorly.

_Action._—A flexor of the toes.

=Flexor Perforans Digitorum Profundus= (Fig. 24, No. 24 and Fig. 25, No.
_G_, 3). _Location._—The posterior tibial region.

_Origin._—From the posterior part of the external condyle of the femur,
from the posterior part of the tibia just below the summit, and from a
point near the origin of the soleus.

_Insertion._—Its heavy flattened tendon passes through the tibial
cartilage, this tendon dividing, the branches pass along the under side
of the toes, perforating the outer tendons and become inserted to the
proximal tubercle at the base of the under side of the ungual phalanxes
of the second, third, and fourth toes.

_Shape._—Long, fleshy, with a long tendon.

_Relations._—Closely with the tibial bone; the deepest of all the
flexors.

_Action._—Flexes the digits.


                         THE MUSCLES OF THE EYE

                     Orbicularis palpebrarum
                     Depressor palpebræ inferioris
                     Pyramidalis nictitans
                     Obliquus inferior
                     Rectus inferior
                     Levator palpebræ superioris
                     Quadratus nictitans
                     Obliquus superior
                     Rectus superior
                     Rectus externus
                     Rectus internus

=Orbicularis Palpebrarum= (Fig. 7, No. 30). (Synonym.—Orbicularis
oculi.)

_Location._—Upon the lacrimal and maxillary bones.

_Origin._—From the lacrimal and maxillary bones and the ciliary margin.

_Insertion._—To the lower free edge of the tarsal cartilage.

_Shape._—Thin, delicate layer of fibers.

_Relations._—Externally, with the skin; internally, with the lacrimal
and the maxillary bones.

_Action._—Aids in closing the eye.

=Levator Palpebræ Superioris= (Fig. 7, No. 24). _Location._—Along the
superior roof of the orbit.

_Origin._—Along a longitudinal line found near the middle of the roof of
the orbit.

_Insertion._—To the ciliary margin of the upper lid, near the outer
canthus.

_Shape._—Thin, delicate layer.

_Relations._—Superiorly, with the bony wall, and inferiorly, with the
eyeball.

_Action._—Raises the superior eyelid.

=Depressor Palpebræ Inferioris= (Fig. 7, No. 29). (Synonym.—Malaris.)

_Location._—Along the inferior border of the eye.

_Origin._—From the inferior border of the interorbital foramen.

_Insertion._—To the lower lid.

_Shape._—Thin, flat, delicate.

_Relations._—Superiorly, with the eyeball; inferiorly, with the inferior
orbital wall.

_Action._—Pulls the lower lid down.

=Quadratus Nictitans= (Fig. 26, No. _B_, 7). _Location._—Above the
eyeball along the inferior border of the upper wall of the orbit.

_Origin._—From the sclerotic from the upper part of the ball.

_Insertion._—To the upper part of the sheath of the optic nerve near the
optic foramen.

_Shape._—Broad, thin, quadrate.

_Relations._—Inferiorly, with the eyeball; superiorly, with the orbital
wall, with the superior oblique, and with the superior rectus.

_Action._—Aids in pulling the nictitating membrane obliquely outward and
downward over the forepart of the eyeball.

=Pyramidalis Nictitans= (Fig. 26, No. _B_, 8).
_Location._—Inferoposteriorly to the eyeball.

_Origin._—From the lower nasal side of the eyeball.

_Insertion._—The fibers converge toward the upper part of the optic
nerve, into a tendon which passes through a pulley at the free margin of
the quadratus. Inserts to the lower part of the margin of the third
eyelid, the nictitans.

_Shape._—Pyramidal; of thin layers of fibers.

_Relations._—Internally, with the bony orbital wall; externally, with
the eyeball.

_Action._—Aids the quadratus nictitans.

=Obliquus Superior= (Fig. 26, No. _B_, 5). (Synonym.—Obliquus dorsalis.)

_Location._—Superior to the eyeball.

[Illustration:

  FIG. 26.—Structures of the eye and nasal passage.

  _A._ 1, The anterior turbinated bone. 2, The posterior turbinated
    bones. 3, Orbital gland. 4, Ophthalmic division of the fifth pair of
    cranial nerves. 5, Section through the cerebrum. 6, Section through
    the skull showing the air spaces. 7, Section through the comb. 8,
    Anterior portion of the upper beak. 9, Edge of the hard palate.

  _B._ The intrinsic muscles of the eyeball. 1, Superior rectus. 2,
    Internal rectus. 3, Inferior rectus. 4, External rectus. 5, Superior
    oblique. 6, Inferior oblique. 7, Quadratus. 8, Pyramidalis. 9, Optic
    nerve. 10, Edge of membrana nictitans.

  _C._ Posterior part of the eye showing at the inferior portion of the
    ball the pyramidalis muscle at 1, and at 2, the quadratus. 3, Optic
    nerve.

  _D._ Inner view of the posterior part of the vitreous chamber. 1,
    Sclerotic coat. 2, Choroid coat. 3, Retina. 4, Pecten.

  _E._ Longitudinal section through the eye of a hen. 1, Cornea. 2,
    Anterior chamber. 3, Scleral ring. 4, Crystalline lense. 5, Iris. 6,
    Retina. 7, Sclerotic. 8, Choroid. 9, Pecten. 10, Optic nerve. 11,
    Vitreous chamber.

  _F._ An edge view of the crystalline lense of a hen showing it to be
    asymmetrical biconvex. 1, The anterior side. 2, The posterior side.

  _G._ The upper section through the anterior portion of the anterior
    turbinated bone showing one complete circle and the lower a section
    through the middle turbinated showing one and one-half turns.
]

_Origin._—From the orbital septum just back of the inner canthus, the
fibers passing backward and forward.

_Insertion._—Into the sclera, anterior to the sclerotic plates.

_Shape._—Small, thin, fan-shaped.

_Relations._—With the eyeball, superiorly; at its extremities with the
superior rectus, interiorly.

_Action._—Rotates the eyeball.

=Obliquus Inferior= (Fig. 26, No. _B_, 6). (Synonym.—Obliquus
ventralis.)

_Location._—Inferior to the eyeball.

_Origin._—From the interorbital septum near the inner canthus of the
eye.

_Insertion._—By a broad expansion to the inferior portion of the
eyeball.

_Shape._—Tendinous at its insertions; fan-shaped as it passes downward
and outward.

_Relations._—Internally, with the eyeball; and externally, with the bony
orbital wall, with the inferior rectus muscle, inferiorly.

_Action._—Aids in rotating the eye; opposes the obliquus superior.

=Rectus Superior= (Fig. 26, No. _B_, 1). (Synonym.—Rectus dorsalis.)

_Location._—Superior to the eyeball.

_Origin._—Along the supero-posterior border of the optic foramen.

_Insertion._—To the sclera just within the margin of the bony circle of
the eye.

_Shape._—Flat, thin.

_Relations._—Internally, with the obliquus superior; superiorly, with
the bony wall of the orbit.

_Action._—To pull the eyeball upward.

=Rectus Inferior= (Fig. 26, No. _B_, 3). (Synonym.—Rectus ventralis.)

_Location._—Inferior to the eyeball.

_Origin._—From the inferior border of the optic foramen.

_Insertion._—To the lower portion of the eyeball within the margin of
the bony circle of the eye.

_Shape._—Thin, fan-shaped.

_Relations._—Superiorly, with the eyeball; inferiorly, with the bony
wall of the orbit.

_Action._—Pulls the eyeball downward.

=Rectus Externus= (Fig. 26, No. _B_, 4). (Synonym.—Rectus lateralis.)

_Location._—External to the eyeball.

_Origin._—By two heads infero-laterally to the optic foramen.

_Insertion._—To the postero-external side of the eyeball.

_Shape._—Short, fan-shaped.

_Relations._—Internally, with the eyeball; externally, with the bony
wall of the orbit.

_Action._—Pulls the eyeball outward.

=Rectus Internus= (Fig. 26, No. _B_, 2). (Synonym.—Rectus medialis.)

_Location._—Inner side of the eyeball.

_Origin._—From the supero-anterior border of the optic foramen.

_Insertion._—To the sclera on the anterior portion of the eyeball.

_Shape._—Thin, fan-shaped.

_Relations._—Internally, with the eyeball and with the pyramidalis;
externally, with the bony wall of the orbit.

_Action._—Pulls the eyeball inward.


                         THE MUSCLES OF THE EAR

                             Circumconcha
                             Tensor tympani

=Circumconcha= (Fig. 7, No. 32). _Location._—Surrounds the external ear.

_Origin and Insertion._—The circumconcha, surrounding the periphery of
the ear, is adherent to the skull and loosely to the skin, and is
attached to the outer terminus of the supra-occipital crest.

_Relations._—Internally, with the skull; externally, with the skin.

_Action._—Relaxes the tympanum.

=Tensor Tympani= (Fig. 7, No. 31). _Location._—External to the quadrate
and to the external auditory meatus.

_Origin and Insertion._—From the surface of the quadrate and the inner
end of the quadrato-jugal to the inner surface of the tympanum.

_Shape._—A few fibers.

_Relations._—Internally, with the quadrate and the quadrato-jugal;
externally, the integumental duplicature.

_Action._—Tenses the tympanum.


                          FUNCTIONS OF MUSCLES

 To cause the feathers on the top of the head to lie flat:
     Dermo-frontalis.
 To raise the feathers along the superior part of the neck and along the
    dorsal region:
     Dermo-dorsalis.

 To tense the patagial region:
     Dermo-tensor patagii,
     Dermo-temporalis.
 To cause the feathers to lie close to the body:
     Dermo-humeralis,
     Dermo-pectoralis.
 To tense the lateral cervical integument:
     Dermo-temporalis.
 To support the lingual apparatus and superior larynx:
     Platysma myoides.
 To manipulate the feathers and skin of the inferior part of the neck:
     Cleido-trachealis.
 To control the skin in the shoulder region:
     Dermo-spinalis.
 To cause the feathers of the back to lie close to the skin:
     Dermo-iliacus.
 To depress the humeral region:
     Dermo-ulnaris.
 To close the jaw:
     Temporalis,
     Pterygoideus internus,
     Pterygoideus externus,
     Masseter.
 To open the jaw:
     Biventer maxilla,
     Entotympanic.
 To raise the trachea and hyoid apparatus:
     Digastricus.
 To elevate the tongue:
     Mylo-hyoideus.
 To pull the tongue to one side:
     Singly[5]—
         Cerato-hyoideus,
         Stylo-hyoideus.
     Alone when the larynx is fixed—
         Sterno-hyoideus.
 Those which protrude the tongue from the mouth:
     Together—
         Cerato-hyoideus,
         Genio-hyoideus.
 To aid in deglutition:
     When the base of the tongue is fixed—
         Sterno-hyoideus.
 To depress the tongue:
     Together—
         Sterno-hyoideus.

 To depress the tip of the tongue and elevate the base:
     Depressor glottis.
 To elevate the hyoid arches:
     Cerato-glossus.
 To extend the head:
     Complexus,
     Rectus capitis anticus minor.
 To flex the head upon the neck:
     Flexor capitis inferior.
 To extend the head on the neck and elevate the neck:
     Biventer cervicis.
 To raise the neck upward:
     Longus colli posticus.
 To flex each vertebra on the preceding or succeeding laterally:
     Obliquus colli,
     Intertransversales.
 To pull the neck downward:
     Longus colli anterior.
 To pull the head downward:
     Together—
         Rectus capitis lateralis,
         Trachelo-mastoideus.
 To pull the head downward and to one side:
     Singly—
         Rectus capitis lateralis,
         Trachelo-mastoideus.
 To approximate the spinous processes of the vertebræ:
     Interspinales.
 To approximate the vertebræ in a supero-lateral direction:
     Interarticulares.
 To flex the vertebræ supero-laterally:
     Obliquo-transversales.
 To extend the neck:
     Together when the first rib is fixed—
         Scalenus medius.
 To close the glottis:
     Constrictor glottidis.
 To open the glottis:
     Thyreo-arytenoideus.
 To approximate the tracheal rings:
     Tracheo-lateralis.
 To tense the inferior larynx:
     Broncho-trachealis posticus,
     Broncho-trachealis anticus,
     Broncho-trachealis brevis,
     Bronchialis posticus,
     Bronchialis anticus.

 To relax the inferior larynx:
     Sterno-trachealis.
 To aid in respiration:
     When the first rib is fixed—
         Intercostales.
     When wing is fixed—
         Latissimus dorsi,
         Dermo-cleido dorsalis.
     When the scapula is fixed—
         Serratus magnus anticus,
         Serratus parvus anticus,
         Thoraco-scapularis,
         Levatores costarum,
         Appendico-costales,
         Triangularis sterni.
 To flex the shoulder-joint:
     Latissimus dorsi.
 To elevate the humerus:
     Latissimus dorsi.
 To draw the scapula forward:
     Trapezius,
     Rhomboideus.
 To close the wing:
     Teres et infraspinatus.
 To extend the humerus:
     Coraco-humeralis,
     Scapulo-humeralis.
 To pull the humerus upward and backward:
     When the scapula is fixed—
         Supraspinatus.
 To pull the coracoid outward:
     Subclavius.
 To depress the wing:
     Coraco-brachialis.
 To depress the scapula:
     When the ribs are fixed—
         Thoraco-scapularis.
 To rotate the humerus:
     Subscapularis.
 To flex the forearm:
     Pronator brevis,
     Biceps,
     Brachialis anticus,
     Anconeus,
     Tensor patagii longus,
     Tensor patagii brevis.
 To extend the arm:
     Deltoid.

 To extend the antibrachial region:
     Triceps.
 To raise and to draw the hand forward:
     Extensor metacarpi radialis longior.
 To extend the digit:
     Extensor indicis longus,
     Extensor digitorum communis,
     Extensor proprius pollicis,
     Interosseous dorsalis.
 To supinate the radial region:
     Supinator brevis.
 To flex the hand:
     Flexor metacarpi radialis.
 To pronate the forearm:
     Pronator brevis,
     Pronator longus.
 To extend the hand on the forearm:
     Extensor ossis metacarpi pollicis.
 To flex the digit:
     Flexor minimi digiti,
     Flexor digitorum sublimis,
     Flexor brevis pollicis,
     Flexor digitorum profundus,
     Interosseous palmaris.
 To flex the hand upon the forearm:
     Flexor carpi ulnaris,
     Flexor carpi ulnaris brevior.
 To rotate the hand toward the body:
     Flexor carpi ulnaris brevior.
 To abduct the digits:
     Abductor minimi digiti.
 To flex the metacarpus:
     Flexor metacarpi brevis.
 To extend the leg:
     Sartorius.
 To adduct the thigh:
     Sartorius,
     Adductor longus,
     Adductor magnus.
 To abduct the thigh:
     Gluteus primus,
     Gluteus medius,
     Gluteus minimus.
 To pull the thigh forward:
     Gluteus minimus,
     Gluteus medius.
 To extend the leg upon the thigh:
     Extensor femoris,

     Vastus internus.
 To extend the leg upon the knee:
     Vastus internus.
 To flex the leg upon the thigh:
     Biceps flexor cruris,
     Semitendinosus,
     Semitendinosus accessorius,
     Semimembranosus.
 To pull the tail down and to one side:
     Femoro-caudal.
 To pull the head of the femur backward:
     Obturator externus.
 To act as a posterior stay to the head of the femur:
     Obturator internus.
 To pull the pelvis forward and to steady it on the head of the femur:
     Gemellus,
     Obturator internus,
     Obturator externus.
 To extend the metatarsus on the tibia:
     Gastrocnemius,
     Soleus,
     Tibialis posticus.
 To flex the toes:
     Peroneus longus,
     Flexor perforatus medius primus pedis,
     Flexor perforatus indicis secundus pedis,
     Flexor perforatus medius secundus pedis,
     Flexor perforatus indicis primus pedis,
     Flexor perforans digitorum profundus,
     Flexor longus hallucis,
     Flexor perforatus annularis primus pedis.
 To flex the metatarsus on the tibia:
     Tibialis anticus.
 To extend the toes:
     Extensor longus digitorum,
     Extensor hallucis brevis.
 To flex the back laterally and to aid in raising the body.
     Sacro-lumbalis,
     Longissimus dorsi.
 To elevate the tail:
     Levator coccygis,
     Levator caudæ.
 To depress the tail:
     Depressor caudæ,
     Infracoccygis.
     Together—
         Depressor coccygis,
         Lateralis caudæ.

 To pull the tail downward and to one side:
     Singly—
     Lateralis coccygis.
         Depressor coccygis,
         Lateralis caudæ.
 To close the eyelids:
     Orbicularis palpebrarum.
 To raise the superior eyelid:
     Levator palpebræ superioris.
 To pull the lower eyelid downward:
     Depressor palpebræ inferioris.
 To pull the membrana nictitans over the eyeball:
     Quadratus nictitans,
     Pyramidalis nictitans.
 To rotate the eyeball:
     Obliquus superior,
     Obliquus inferior.
 To pull the eyeball upward:
     Rectus superior.
 To pull the eyeball downward:
     Rectus inferior.
 To pull the eyeball outward:
     Rectus externus.
 To pull the eyeball inward:
     Rectus internus.
 To tense the ear drum:
     Tensor tympani.
 To relax the ear drum:
     Circumconcha.
 To depress the humerus:
     Pectoralis major.
 To raise the humerus:
     Pectoralis secundus,
     Pectoralis tertius.

Footnote 5:

  Muscles are arranged in pairs. Singly means one muscle acting alone,
  _i.e._, without its fellow; together means acting both at the same
  time.




                             SPLANCHNOLOGY


=The Digestive Apparatus.=—This apparatus, apparatus digestorius,
consists of the organs directly concerned in the reception of food, in
its passage through the body, and in the expulsion of the unabsorbed
portion. For convenience, these organs are grouped as follows: the
alimentary canal and the accessory organs.

The alimentary canal is a tube which extends from the mouth to the anus.
It has a complete lining of mucous membrane, external to which is an
almost continuous muscular coat. The abdominal portion of the tube is
largely covered with a serous membrane, the visceral peritoneum. The
canal consists of the following consecutive segments: mouth, pharynx,
first portion of the esophagus, crop, second portion of the esophagus,
proventriculus, gizzard, small intestine, large intestine, and cloaca.

The accessory organs are beak, tongue, salivary glands, liver, and
pancreas.

=The Mouth= (Fig. 27).—The distinctive character of the mouth of the
fowl consists, in the absence of lips and teeth and instead of jaw bones
of other animals, of a _beak_. The edge of the beak is covered by a
horn-like gum. The shape of the beak differs in the various classes of
birds. In the chicken the beak is short, strong, thick, and pointed; in
palmipeds it is flattened. The upper mandible extends out over the lower
mandible. The outer portion of the upper and the lower beaks is covered
by a horny sheath. There is no velum, and the mouth cavity is extended
rather continuously into the pharynx (Fig. 27, No. 4). The posterior
cross bar of the hard palate (Fig. 27, No. 5), which possesses a row of
filiform papillæ projecting backward, marks the upper boundary line of
the mouth; while the posterior end of the tongue (Fig. 27, No. 6),
likewise with a row of filiform papillæ, marks its lower boundary line.

_Parts of the Mouth._—The mouth of fowls is divided into an upper and a
lower half. The upper half is divided into an anterior and a posterior
part.

The anterior part extends from the anterior tip of the beak to the
posterior nares. It is further divided into an outer hard part and an
inner soft part. The outer part is covered by epithelium which may be
considered as a continuation from the upper outer portion of the beak. A
portion of this is cornified. The inner part is covered by a mucous
membrane containing mucous glands, nerves, and blood-vessels.

In the posterior part of the upper half of the mouth, are situated the
posterior nares (Fig. 27, No. 10) which appear as a longitudinal slit in
the center of the hard palate. There is also found in this part a furrow
which contains the opening of the Eustachian tubes, or tubæ auditivæ.
There are also two ridges near the same posterior part in which are red
and white papillæ, which may appear in rows, and which contain mucous
glands.

[Illustration:

  FIG. 27.—Mouth and pharynx of a cock laid open. 1, Eye. 2, Edge of
    beak covered with a horn-like gum. 3, Tongue. 4, Pharynx. 5,
    Posterior cross bar of hard palate. 6, Posterior end of tongue. 7,
    Anterior end of esophagus. 8, Phrenum. 9, Palatal papillaries. 10,
    Posterior nares.
]

The lower half of the mouth lies between the lower jaw bones and the
walls of the mouth cavity. The tongue is attached here by means of the
phrenum (Fig. 27, No. 8). This half of the mouth forms a pocket-like
structure which aids in taking up the food.

The mouth cavity is lined with stratified squamous epithelium,
continuous with that of the pharynx and the esophagus. Taste buds are
located in the mucous membrane of the mouth.

[Illustration:

  FIG. 28.—Various anatomical parts of the fowl.

  _C._ A section through the nasal region of the fowl. 1, Nasal passages
    showing the turbinated bones dividing the nasal passage into the
    superior, middle and inferior meati. 2, The infraorbital sinus. 3,
    The hard palate.

  _D._ Herbst’s touch corpuscle from the beak of a quail.

  _E._ A vertical section through the ductus cochlearis of a pigeon. 1,
    A blood-vessel. 2, The periosteum. 3, The bony structure. 4, The
    vascular integument. 5. The scala vestibuli. 6, The inner hyaline
    cylindrical cells. 7, The membrana tectoria. 8, The papilla acustica
    basilaris. 9, The membrana basilaris. 10, The scala tympani. 11, The
    ganglion of the cochlear nerve in the ramus basilaris. 12, The
    periosteum (Gadow).

  _F._ A corpuscle of the soft papilla of a duck’s tongue.

  _J._ A transverse section through a feather papilla. 1, The pulp. 2,
    The malpighian layer. 3, The corium. 4, The stratum corneum of the
    papilla. 5, The malpighian cell group of the main shaft. 6, The
    horny sheath.
]

In many water fowls, as geese and ducks, the gum edge of the mandible
has grooves extending crosswise, in which are numerous terminals of the
trigeminus nerve arranged as taste organs (Fig. 29, _G_ and Fig. 28, _D_
and _F_). In many birds of prey and in water birds, _e.g._, the goose
and the duck, there is found at the base of the beak, a very thin,
nervous or sensitive skin, waxy in appearance, called the ceroma.

[Illustration:

  FIG. 29.—Various anatomical parts of the fowl.

  _A._ 1, The superior semicircular canal. 2, The vestibular nerve. 3,
    The meatus auditorius internus—the entrance of the auditory nerve.
    4, The entrance of the cochlear nerve. 5, Posterior semicircular
    canal. 6, The ampulla.

  _B._ Side papilla of the tongue. 1 and 2, Papillæ showing a fibrous
    central core supporting blood-vessels and nerves. 3, The basement
    membrane consisting of connective tissue.

  _G._ Herbst’s corpuscle of the tongue of a duck, showing the capsule,
    lamella and around the nerve zone, numerous round bodies arranged in
    two rows.

  _H._ From the cristæ acoustica of the ampulla of the dove. A, A
    vertical section with isolated fiber cells. 1 and 2, The nerve
    fibers. 3, The hair cells.

  _I._ A longitudinal section through a feather papilla showing a young
    feather. 1, The developing feather. 2, The horny sheath. 3, The
    epithelium. 4, Stratum corneum. 5, Stratum malpighi. 6, Corium. 7,
    Malpighian cell group of the follicle.
]

_The Hard Palate._—The hard palate, palatum durum, forming the roof of
the mouth has for its boundaries the beak anteriorly, the mandibular
arches laterally, and the pharynx posteriorly. It has four or five
transverse bars, projecting posteriorly from each of which is a row of
filiform papillæ (Figs. 27 and 29).

[Illustration:

  FIG. 30.—A section through the wall of the crop of a hen. 1, The outer
    muscular layer showing longitudinal fibers. 2, The inner muscular
    layer showing the sectioned ends of the bundles of muscle fibers. 3,
    Stratified squamous epithelium. 4, The outer surface or lumen of a
    fold. 5, The stroma, muscularis mucosa, and submucosa.
]

The _beak_ (Fig. 4, No. 1) with little if any aid from the tongue, is
the prehensile organ.

=The Tongue= (Fig. 27, No. 3). _Location._—The tongue (lingua) of the
fowl is situated in the floor of the mouth between the rami of the lower
mandible, and is slung to the cranium by the cerato-branchial element of
the os hyoideum (Fig. 18, No. 2).

_Shape._—The tongue, is pointed in front and wide behind, shaped like an
Indian arrow-head, and is supported by the bony and cartilaginous hyoid
apparatus (Fig. 9, _A_).

[Illustration:

  FIG. 31.—The visceral organs of the hen. 1, Tongue. 2, Larynx. 3,
    Glottis. 4, First portion of the esophagus. 5, Crop. 6, Second
    portion of the esophagus. 7, Proventriculus. 8, Duodenum. 9, Free or
    floating portion of the small intestine. 10, Mesentery supporting
    the free portion of the small intestine. 11, Cæca. 12, Rectum or
    large intestine. 13, Cloaca. 14, Anus. 15, Liver. 16, Gall-bladder.
    17, Pancreas. 18, Gizzard. 19, Trachea. 20, Lungs. 21, Spleen.
]

_Structure._—The free part of the tongue consists of two long tubes
which are formed by the rolling in of the ventral sides of its horny
coverings. The _dorsal plate_, which constitutes one-half of the horny
sheath, does not form a part of the tubes, but ends in the region of the
point of the entoglossum.

The top surface is covered by a thick stratum corneum, giving it a
rather horny surface. Glands occur in the posterior part of the tongue.

While not so freely movable as in mammals, the tongues of birds are very
flexible.

=The Pharynx= (Fig. 27). _Location._—The anterior part of the pharynx
joins with the mouth and the posterior part with the upper portion of
the esophagus and the superior larynx. The pharynx is bounded anteriorly
by the base of the tongue and by the posterior edge of the hard palate.
Posteriorly, it is marked by the entrance of the esophagus and by a
ridge of filiform papillæ located on the supero-posterior part of the
larynx, called the palatal papillaries. A few filiform papillæ stud the
roof. The pharynx communicates anteriorly with the posterior nares and
the mouth, and, posteriorly, with the esophagus and the larynx.

_Shape._—The pharynx is a musculo-membranous sac.

_Structure._—The pharynx is lined with a mucous membrane covered by
squamous epithelium. The mucous membrane is thrown into irregular folds.
The bird has two Eustachian tubes. Pneumatic apertures conduct the air
from the Eustachian tubes to the pericranial diploë.

In the posterior pharyngeal roof is situated the infundibular crevice.

_Function._—The function of the pharynx is to give passage for the air
from the posterior nares to the larynx, and to give passage for the food
from the _mouth_ to the esophagus.

=Glands Adjacent to the Mouth and to the Pharynx.=—The mucous membrane
adjacent to the glottis and in the roof of the mouth contains alveolar
glands. The _angular gland_ of the mouth, located beneath the zygomatic
arch, by some anatomists is considered the rudimentary parotid gland.
The _sublingual glands_, or glandulæ sublinguales, are well developed
(Fig. 17, No. _B_, 4). They form conical masses, with the apex directed
anteriorly, and occupy a portion of the intermaxillary space. Several
ducts from these glands open into the mouth cavity. In the palatine
region there are also located glands called the _palatine glands_, which
open by many stomata upon the surface.

=The Esophagus= (Fig. 18, No. 6). _Location and Shape._—The esophagus is
a musculo-membranous tube, capable of great distension, which extends
from the pharynx to the proventriculus (Fig. 35, No. 1, and 3).

The esophagus communicates anteriorly with the pharynx. It extends down
the neck, lying supero-laterally with regard to the trachea and toward
the right side. It enters the thorax above the trachea, and, passing
through between the bronchi, terminates into the proventriculus. At the
entrance of the thorax and just to the right of the median line, it
expands into the crop which divides it into two portions, designated as
the first and the second. The first portion of the esophagus is the
longer, the length depending upon the size and kind of fowl.

_Structure._—The wall is composed of four coats, the mucous membrane,
the submucosa, the muscular coats, and the fibrous sheath or tunic. The
mucous membrane is pale and is covered with stratified squamous
epithelium.

The mucous membrane is loosely attached to the muscular coat by the
submucosa. Except during deglutition it lies in longitudinal folds which
obliterate the lumen. Opening from the mucosa are lenticular glands,
which may be seen on inflating an esophagus and looking through its
transparent walls.

The muscular coat of the esophagus is divided into two layers, an outer
longitudinal and an inner circular layer.

The outer fibrous sheath connects the esophagus loosely to the
surrounding structures.

_Function._—The function of the esophagus is to give passage way for the
food from the pharynx to the crop and from the crop to the
proventriculus.

=The Crop= (Fig. 35, No. 2; Figs. 30 and 31). _Location and Shape._—The
crop, or ingluvies, saccular in shape, is located at the entrance of the
thorax and just to the right of the median line. The first portion of
the esophagus empties into the crop superiorly and inferiorly the crop
opens into the second portion of the esophagus. Like the esophagus the
crop is capable of great distension.

_Structure._—The wall of the crop is composed of four coats, the mucous
membrane, submucosa, muscular and the outer fibrous.

The crop is lined with mucous membrane containing mucous glands which
secrete a mucus to keep the surface moist. The surface of the mucous
membrane is covered by stratified squamous epithelium.

The submucosa connects the mucous membrane to the muscular coat.

The wall of the crop is provided with strong muscles. The fibrous coat,
or tunic, connects it with the surrounding structures.

_Function._—The crop is a storehouse for the food during the hours of
feeding, the food when needed by the stomach being gradually discharged
from the crop by the contraction of its muscular walls. The subcutaneous
cervical muscles which cover this reservoir aid in this discharge.

In the _act of deglutition_, the food, after being subjected to the
fluid supplied in the mouth by the adjacent glands, is poised upon the
tongue and swallowed partly by a sudden jerk of the head, and partly by
means of the pressure of the tongue against the hard palate, the food
then passes down the esophagus and lodges first in the crop, till needed
by the stomach, when it is passed through the second portion of the
esophagus to the first portion of the stomach, the proventriculus. The
time during which food remains in the crop depends upon the nature of
the food. Animal food will, in part, be retained about eight hours and
vegetable foods may not all be passed on for from sixteen to eighteen
hours.

=The Stomach= (Fig. 31, No. 7; Fig. 32, _B_).—The stomach, or
ventriculus, of fowls is made up of two portions, namely, the pars
glandularis, or proventriculus, and the pars muscularis, or gizzard.

=The Proventriculus.= _Location._—The proventriculus lies in the
superior part of the groove formed by the two lobes of the liver, is
inferior to the aorta, and is directed slightly to the left,
communicating anteriorly with the second portion of the esophagus and
posteriorly emptying into the pars muscularis, the gizzard.

_Shape._—The proventriculus is round transversely and elongated, in
fact, nearly fusiform. In the hen of average size it measures about 1.62
inches long and 0.8 inch in diameter.

_Structure._—The wall of the proventriculus has four coats, the mucous,
submucous, muscular, and serous.

The inner mucous coat which is raised in folds, is lined with columnar
epithelial cells. The mucous membrane contains lymphoid tissue. The
mucous coat throughout contains simple tubular glands which secrete a
highly acid fluid which finds its way to the surface through small
cylindrical ducts lying at right angles to the inner surface of the
mucous membrane (Fig. 32, No. _B_, 1).

[Illustration:

  FIG. 32.—Gizzard and stomach of the fowl.

  _A._ 1, Alveolar glands. 2, Mucous membrane of the inner surface of
    the proventriculus showing the tubular glands. 3, Connective tissue
    between the alveolar glands. 4, An artery. 5, Muscularis mucosa.

  _B._ Photograph of the proventriculus and gizzard. 1, Proventriculus
    showing stomata of glands. 2, End of duodenum. 3, Gizzard showing
    hornified epithelium formed into grooves. 4, The heavy muscular
    walls.
]

The submucosa, connects the mucous and muscular coats and the muscularis
layer throws the mucous membrane into folds.

Outside the muscularis mucosa there is another layer (Fig. 32, _A_), of
simple tubular glands, grouped in lobules, and lined by cuboidal cells
and separated from each other by clefts. These tubular glands converge
toward the center and open into the same cavity.

The middle muscular coat can be divided into three layers: two thin,
longitudinal layers, and a thick, circular layer interposed between the
other two.

_Function._—The function of the proventriculus appears to be to soak the
food with a secretion. The secretion from the proventriculus is similar
to that produced by the fundus glands of the stomach of mammals. It
contains acid and a ferment-pepsin.

=The Gizzard= (Fig. 31, No. 18). _Location._—The gizzard, or muscular
stomach, occupies a portion of the central part of the abdominal cavity
(Fig. 33, No. 4). It lies slightly to the left and just behind the
liver, the proventriculus, and the spleen, and rests upon a mass of
intestines. The gizzard communicates at its anterior portion with the
proventriculus and with the duodenum. These openings are close together.
The gizzards of a large number of hens of average size averaged in
weight as follows: full, 0.215 pound; empty, 0.126 pound. The gizzard
stands perpendicularly and somewhat obliquely in the abdominal cavity.

_Shape._—In shape the gizzard is roundish, flattened laterally.

_Structure._—The walls of the gizzard are very thick and are made up of
three coats: mucous, muscular, and serous.

The cavity of the gizzard is covered by a thick skin-like structure
possessing a heavy stratified squamous epithelial layer which is thrown
somewhat into ridges (Fig. 32, _B_). This membrane becomes thinnest near
the edges.

The mucous membrane, being cornified and readily detachable, is by some
anatomists considered as a special membrane (Fig. 37, _B_).

At the pyloric opening there is a valve formed by a fold of the mucous
membrane, which prevents grit and large particles of food from passing
out of the gizzard.

[Illustration:

  FIG. 33.—View of viscera of the left side of a hen. 1, The base of the
    heart. 2, Proventriculus. 3, Left lobe of the liver. 4, Gizzard. 5,
    End of the duodenal loop. 6, Pancreas. 7, Free portion of the small
    intestine. 8, Lungs. 9, Diaphragm.
]

[Illustration:

  FIG. 34.—View of the viscera of the right side of a hen. 1, Base of
    the heart. 2, Lungs. 3, Right lobe of the liver. 4, Duodenal loop.
    5, Pancreas. 6, Cæcum. 7, Large intestine or rectum. 8, Free portion
    of the floating small intestine. 9, Gall-bladder. 10, Right kidney.
    11, The ribs. Note the lungs pushing up between them.
]

On each side it has a powerful fleshy muscle, the _muscularis
lateralis_. These musculares laterales are hemispherical, consist of
very closely packed fibers extending transversely, and are attached to
strong anterior and posterior ligamentous tendons. They are joined at
the edge of the organ by a strong aponeurosis. The muscular fibers are
red but do not possess cross striations; they are of the smooth type.
The _muscularis intermedii_, thinner and less developed than the
musculares laterales, occurs on each of the anterior and the posterior
parts of the gizzard.

The serous coat covers over the greater part of the external surface of
the gizzard and closely adheres to the muscular coat.

_Function._—The hard callous pads of the gizzard, operated by the
powerful muscles above described, together with grit, act like mill
stones and make reduction to fineness very complete.

At the posterior part there is a sacculated portion containing glands of
the long tubular type which secrete a fluid ferment similar to that
secreted by the glands of the pyloric portion of the stomach of mammals.
These glands also exist in a small band near the entrance of the
gizzard. Here the food is mixed with strongly acid secretion containing
pepsin which makes gastric digestion perfect.

[Illustration:

  FIG. 35.—A median antero-posterior section through the body of a
    1-pound pullet. 1, First portion of the esophagus. 2, Crop. 3,
    Second portion of the intestine. 4, Proventriculus. 5, Gizzard. 6,
    Spleen. 7, Liver. 8, Heart. 9, Point where duodenum was severed from
    gizzard. 10, Point where duodenum was severed. 11, Duodenum. 12,
    Pancreas. 13, Cæcum. 14, Floating small intestine. 15, Ovary. 16,
    Oil sac.
]

=The Small Intestine= (Fig. 31, No. 8 and 9).—The small intestine,
intestinum tenue, is the tube which connects the gizzard with the large
intestine. It is divided into two parts, the duodenum and the free
portion. Of the three parts as considered in the mammalian intestine,
only the first, the _duodenum_, can be distinguished. There is no
demarcation between the jejunum and the ileum. The jejunum and the ileum
or that part which represents these sections, are in coils suspended
from the free border of the mesentery the other border of which is, in
turn, attached to the dorsal wall (Fig. 64). The length of the small
intestine in a hen of average size is about 61.7 inches.

[Illustration:

  FIG. 36.

  _A._ Section of the duodenum of the fowl. 1, Villus. 2, Gland. 3, Mass
    of lymphoid tissue. 4, Muscularis mucosa. 5, Longitudinal layer. 6,
    Circular muscular layer. 7, Serous layer.

  _B._ A section from A at _a_. 1, The striated free border of the
    cells. 2, Goblet cell. 3, Columnar cell. 4, Nucleus of cell.
]

The wall of the small intestine is provided with four coats, as follows:
a mucous, submucous, muscular coat made up of two layers—the outer,
longitudinal and the inner circular layer, and an external serous.

[Illustration:

  FIG. 37.—Histological studies of various anatomical parts.

  _A._ A transverse section of the first portion of the esophagus of a
    fowl. 1, The outer longitudinal muscular layer. 2, The circular
    muscular layer. 3, The submucosa. 4, The muscularis mucosa. 5,
    Stroma. 6, Epithelial layer. 7, The lenticular glands. 8, The lumen.

  _B._ A transverse section of the proventriculus. 1, The outer
    longitudinal muscular layer. 2, The middle muscular layer. 3, The
    inner longitudinal muscular layer. 4, Stroma. 5, The muscularis
    mucosa. 6, The submucosa. 7, Stroma. 8, Tubular glands. 9,
    Tubulo-alveolar glands. 10, A tubulo-alveolar gland with the tubular
    glands cut transversely, 11, The lumen of the proventriculus.

  _C._ A section of the inner wall of the gizzard. 1, The hyaline mucous
    membrane. 2, Branched tubular glands. 3, Submucosa. 4, Muscle. 5, A
    connective tissue septum.

  _D._ A transverse section of the small intestines. 1, The outer
    longitudinal muscular layer. 2, The inner circular muscular layer.
    3, The muscularis mucosa. 4, The stroma. 5, Brunner’s glands. 6, A
    villus. 7, Mass of lymphoid tissue.

  _E._ A transverse section through the cecum. 1, The outer longitudinal
    muscular layer. 2, The inner circular muscular layer. 3, The
    submucosa. 4, The muscularis mucosa. 5, The stroma. 6, Tubular
    glands. 7, The lumen.

  _F._ The cerebellum showing the arbo-vitæ. 1, White, fiber portion. 2,
    The granular layer. 3, The layer of Purkinje cells. 4, The molecular
    layer.
]

The mucous membrane which lines the intestine is thick, soft, and highly
vascular. It has a velvety appearance, due to numerous long, thin
projecting _villi_. The villi (Fig. 36, _A_) are concerned in the
absorption of the digested food, absorbing principally the emulsified
fats. Each villus is covered with a single layer of high columnar
epithelial cells. Some of these, the so-called goblet cells, provide
mucin which lubricates the mucous surface. These cells are found in all
mucous surfaces and prevent the surface from becoming dry. There are a
few goblet cells near the summits of the villi. Openings of simple
intestinal tubular glands the duodenal glands, or the glands formerly
known as _Brunner’s glands_, are located between the villi. These glands
secrete the succus entericus, or intestinal juice. These openings, or
stomata, are lined with granular cells. The reaction of the contents of
the small intestine is strongly acid, but gradually less so in
proportion to the distance down the intestinal tract until the cæca are
reached, where the reaction is found to be faintly acid, neutral, or
slightly alkaline.

_Function._—The function of the small intestine is that of digestion and
absorption.

=The Duodenum.= _Location and Shape._—The duodenum, a small tube,
originates from the gizzard about ½ inch to the right of the entrance of
the proventriculus. Extending from left to right, it passes under and
behind the gizzard along the inner side of the right abdominal wall
backward to the posterior portion of the wall, and a trifle more than
half way toward the left side, where the loop rests. This loop, the
duodenal loop, is about 5 inches in length (Fig. 31, No. 8). The two
branches of the loop the first and the second portions or the descending
and ascending limbs, are loosely held by connective tissue, and have the
pancreas lodged between them.

=The Free Portion of the Small Intestine.= _Location._—That section of
the small intestine following the duodenum is called the free portion of
the small intestine and occupies the space between the abdominal air-sac
and the median line of the abdominal cavity. It is disposed in coils and
is suspended from the dorsal wall of the abdomen by a thin membrane, the
mesentery.

The bile ducts enter the small intestine about 14 inches from its point
of origin. The pancreas also pours its contents into the small
intestine.

=The Large Intestine= (Fig. 31, No. 12). _Location._—The large intestine
extends in a straight line along the inferior border of the vertebral
column communicating anteriorly with the small intestine, and the cæca
and posteriorly with the cloaca.

_Shape._—The diameter of the large intestine is approximately twice that
of the small intestine. In fowls of average size its mean length is 4.61
inches. The large intestine has sometimes been spoken of as the rectum,
or straight gut.

_Structure._—Like the small intestine the large intestine has four
coats: an inner mucous, a submucous, a middle muscular and an outer
serous. The folds of mucous membrane of the large intestine have tubular
glands lined with columnar cells (Fig. 37, _A_, No. 1).

_Function._—The large intestine is similar in function to that of the
small intestine, in that digestion and absorption may take place within
it.

=The Cæca= (Fig. 31, No. 11). _Location._—The fowl has two cæca
extending forward from their point of origin at the juncture of the
small and large intestine.

_Shape._—The cæca average 7.61 inches in length. They are large in
caliber toward the blind extremity and are constricted near their
origin.

_Structure._—The parietal coats are continued from the small intestine.

Ebarth has described an elevated body in the cæcum, which is located
about 4 millimeters from the opening and is composed entirely of
lymphoid tissue.

[Illustration:

  FIG. 37_A_.—Photomicrograph of a transverse section of large intestine
    and oviduct just anterior to the cloaca, showing the tubular glands
    of the large intestines, mucosa of oviduct with intervening
    structures. 1, The tubular glands of large intestine, or rectum. 2,
    Muscular wall of intestine. 3, Wall of the oviduct. 4, Mucosa of the
    oviduct.
]

The cæca are usually partly filled with a soft pultaceous material of a
pasty consistency.

=The Cloaca= (Fig. 31, No. 13). _Location._—The rectum opens by a
circular, valvular orifice into the dilated portion just in front of the
anus, which dilatation is called the cloaca.

_Shape._—The cloaca is saccular in shape.

_Structure._—The cloaca is divided into two portions, the coprodeumal
and the urodeumal. That portion of the cloaca into which the intestine
empties is called the _coprodeum_; and the ureter and oviduct empty into
the _urodeum_. The seminiferous tubules, carrying the semen from the
testes in the male empty in teatlike projections on the cloacal mucous
membrane into the urodeumal portion. The cloacal walls are similar in
structure to the large intestines.

On the dorsal wall of the cloaca between it and the spine, is a small
sac, called the _bursa of Fabricius_, which has a duct communicating
with the cloaca. The mucous membrane of this sac is thrown into folds
and is studded with glands. The bursa of Fabricius is larger in the
young than in the adult bird. It apparently atrophies as the bird
becomes older. When the bird is four months old this bursa is best
developed, and at this age it may be as large as 2 or 3 centimeters in
diameter.

_Function._—The function of the cloaca is to give passage way to the
feces, the urine, and the egg and to act as an organ of copulation.

=Course of the Food.=—The food first enters the mouth, after being
picked up by aid of the beak. From here it passes through the pharynx
and first portion of the esophagus to the crop, without mastication, as
the bird is not provided with teeth. The food is passed from the crop by
aid of its muscular walls as needed; thence through the second portion
of the esophagus to the proventriculus, an expansion in the digestive
tube just before it terminates in the gizzard. The glands of the
proventriculus produce a secretion in which the food is soaked before
passing into the gizzard. The gizzard is provided with strong muscular
walls which, by aid of grit, thoroughly reduce the food to fineness.
From the gizzard the food passes through the first portion of the small
intestine, where it is subjected to the action of the bile from the
liver, the pancreatic juice from the pancreas, and of the succus
entericus from the glands of the intestinal wall. The food is then
passed into the cæca. The indigestible portion of the food passes from
the cæca through the large intestine, or rectum, to the cloaca and
thence to the external world.

The digestive functions of the bird are very potent and rapid. This
compensates for the waste caused by their extensive, frequent, and
energetic motions, and is in accordance with the rapidity of their
circulation and their high state of irritability.


                   THE ACCESSORY ORGANS OF DIGESTION

The accessory organs of digestion are the liver, pancreas, and some
anatomists include also the spleen. The first two manufacture fluids
containing ferments which aid in splitting or digesting the food.

=The Liver= (Figs. 31, 33 and 34). _Location._—The liver, hepar, lies
ventrally and posteriorly to the heart. It is related anteriorly with
the diaphragm, inferiorly with the sternum, posteriorly with the gizzard
and intestine, and superiorly with the ovary, oviduct and proventriculus
and laterally with the abdominal wall.

_Shape._—The liver is a voluminous deep livid brown gland, soft and
friable in texture. It is divided into two principal lobes, a right and
a left.

The right lobe is larger than the left. In the hen of average size the
liver weighs 35 grams. The parietal surface is convex and smooth. The
surface which lies against the viscera is irregularly concave. The
visceral surface furnishes exit for the bile duct and passage for the
nerves and blood-vessels. This part is called the porta.

The left lobe may be cleft from below so deeply as to form two lobes on
that side.

_Structure._—Each lobe is covered by a double serous membrane, one
closely adherent, the other surrounding the structure loosely. These
tunics, which are reflections of the peritoneum, are continued from the
base of the liver, over both the anterior, and the posterior surface.
The loose layer is formed by the air cells surrounding the lobes. The
thin border of the liver is usually free.

The two lobes of the liver are connected by a narrow isthmus of liver
tissue. Occasionally there is a bird in which there occurs a _lobus
Spigelii_ located at the posterior of the liver between the two
principal lobes.

The apex of the heart sacculates the diaphragm backward, so that part of
this apex lies between the right and the left lobes (Fig. 43, No. 6 and
7). A ligament, the _falciform_, extends from the apex of the
pericardial membrane, and attaching it rather firmly to the central
connective tissue, or interlobar ligament. This ligament also has
attachments to the inner surface of the sternum. The _broad ligament_ of
the liver is formed posteriorly by a fold of the peritoneum.

The _interlobar_, or _principal, ligament of the liver_ is formed by a
large and strong duplicature of the peritoneum, which makes a
longitudinal division in the abdominal cavity similar to the lateral
division made by the thoracic mediastinum in mammals. It is reflected
upon the pericardium from the linea alba and the middle line of the
sternum, and passes deeply into the interspace of the lobes of the
liver. It is attached to these lobes throughout their whole length and
connects them below to one side of the gizzard. The lateral and
posterior part of the liver attach to the adjacent air cells, and the
whole viscus is thus kept fixed in its position during rapid and violent
movements of the bird.

The remains of the umbilical veins are traceable within the duplicature
of the membranes forming the septum. These remains thus represent the
round ligament of mammals.

[Illustration:

  FIG. 38.—Cellular structure of liver, pancreas, and trachea.

  _A._ Liver. 1, Liver cells. 2, Sinusoid. 4, Nucleus of cells.

  _B._ Pancreas. 1, Island of Langerhans. 2, Alveolar cells. 3, Duct.

  _C._ Trachea. 1, Ciliated epithelia. 2, Glands. 3, Hyaline cartilage.

  _D._ Section of wall of ovum at Fig. 57 letter _d_. 1, Yolk. 2,
    Granular membrane. 3, Theca. 4, Blood-vessel.
]

A microscopic study of the liver of the fowl shows a compact mass of
liver cells polyhedral in shape, with large nuclei (Fig. 38, _A_). The
liver tissue differs from that of mammals in that there is no clearly
outlined lobular arrangement; neither is the outline of the individual
cell so well marked. The parenchymatous portion is made up of columns of
liver tissue. These columns anastomose and show narrow channels between.
They are best seen in the young chick.

_Function._—One of the functions of the liver is to secrete bile. A
_gall-bladder_, which receives part of the bile secreted by the right
lobe of the liver, is located on the posterior face of this lobe.
Extending from this gall-bladder there is a duct, the _cystic duct_,
which empties into the small intestine toward the extremity of the
second branch of the duodenal loop. Another duct called the _hepatic
duct_, proceeds directly from the two lobes of the liver and empties
into the intestine just in front of the cystic duct.

=The Pancreas= (Fig. 31, No. 17). _Location and Shape._—The pancreas, an
organ lying in the duodenal loop is a yellowish-white, lobulated gland,
elongated in shape. Its average length in fowls of average size is 4.96
inches, and the average weight about 0.008 pound. The pancreas is
divided into lobes, which in turn are divided into lobules.

_Structure._—The pancreas has a supporting connective tissue. The
lobules are made up of small alveolar glands, which are lined with
columnar epithelial cells. The ducts leading from the alveoli are small;
these unite to form larger ducts in which the epithelium is taller.
Between the alveoli throughout the pancreas there are clusters of
polyhedral cells which form the _islands of Langerhans_. These islands
are said to produce an internal secretion, or hormone, which is absorbed
by the blood or lymph capillaries and thus enters the circulation (Fig.
38, _B_).

_Function._—The function of the pancreas is to secrete a fluid
containing digestive ferments.

=The Spleen= (Fig. 31, No. 21). _Location._—The spleen, or lien, lies in
a triangle formed by the proventriculus, the liver, and the gizzard.

_Shape._—It is a reddish-brown body shaped like a buckeye, is small in
size, weighing only about 0.005 pound.

_Structure._—The outer surface of the spleen is covered by a reflection
of the peritoneum. After this covering is removed, there is observed a
firm, white, fibrous layer, the _cortical portion_. This covering sends
into the interior small and large trabeculæ, forming a framework and
dividing it into acini, or compartments. The spaces are filled with a
dark red parenchymatous material called _splenic pulp_. The framework,
in both deep and surface portions, are found elastic fibers and smooth
muscular fibers.

The spleen is essentially a lymphatic organ, its peculiar structure
depending largely upon the arrangement of the blood-vessels. Compact
lymphatic tissue occurs in the spleen in spherical, oval, or cylindrical
collections of closely packed lymphoid cells. These masses are known as
the _Malpighian bodies_, or _splenic corpuscles_. They are distributed
throughout the splenic pulp. Each splenic corpuscle contains one or more
small arteries. These extend near the periphery of the corpuscle and
more rarely in the center.

The splenic artery passes in and the splenic veins out at the hilum
which is located on the concave, or attached, side of the spleen. The
splenic artery, upon entering the organ, at once branches, the trabeculæ
forming a support for the vessels.

After the arteries have entered the hilum, as stated above, they divide
into many branches which follow the septa of the connective tissue. At
first the arteries are accompanied by branches of the splenic veins.
Soon, however, the arteries leave the veins and the septa, and penetrate
the splenic pulp. In the splenic pulp the adventitia of the smaller
arteries assume the character of reticular tissue, and become
infiltrated with lymphoid cells. This infiltration forms masses which
are called the splenic corpuscles, or Malpighian bodies. The terminal
arteries break up into capillaries, which still retain an adventitia,
and empty into border spaces, or sinuses, sometimes spoken of as
ampullæ. These sinuses in turn empty into cavernous sinuses of the
splenic pulp. From these are finally formed the venules; and the
collections of venules form the splenic veins through which the blood
gains exit from the spleen.

=The Abdominal and Pelvic Cavities.=—In birds the abdominal cavity is
divided into two smaller cavities by a fibrous septum. The anterior
cavity representing the abdominal contains the liver, and the other
representing the pelvic contains the gizzard, intestines and oviduct.

=The Peritoneum and the Mesentery.=—The abdominal and pelvic cavities
are lined by the peritoneum. Like all serous membranes this is composed
of a parietal and a visceral portion, which together form a complete
sac, with the organs it covers situated on the outer side. The
peritoneum like other serous membranes consists of a mesothelial and a
submesothelial portion, the cells of the former being arranged in a
single layer. Since a serous membrane is so arranged as to line a closed
cavity, and at the same time to cover its contents, it follows that the
entire membrane must be a closed sac, the mesothelial layer being on the
inside; such a sac is called a serous sac, or cavity. Synovial membranes
are also regarded as a variety of serous membranes. The fold, or layer,
of the membrane which lines the cavity is called the parietal, that
which covers the greater part of the organs contained therein is called
the visceral portion; the two surfaces contacting, and gliding upon each
other, are lubricated by a fluid secretion contained in the sac; hence
one use of these membranes is to prevent friction between the walls of
cavities and the organs contained therein. Serous membranes line the
abdominal cavity, pericardium, cavities of the heart and is continuous
throughout the vascular structures.

[Illustration:

  FIG. 39.—A transverse section of body of hen through 15, Fig. 34. _R_,
    Right side. _L_, Left side. 1, Spinal cord. 2, Esophagus. 3,
    Trachea. 4, Skin. 5, Pectoral muscles.
]

The serous membrane besides covering the external surface of the
viscera, double folds pass from one organ to another, or from an organ
to the parietes of the cavity. These double folds of the peritoneum are
known as ligaments, or as mesenteries. In ligaments the two folds are
strengthened by an interposed layer of fibro-elastic tissue. A
_mesentery_ is a broad, double fold of peritoneum, attached to the
abdominal parietes above, and containing a portion of the intestine in
its free or remote extremity. Between its folds we find blood-vessels,
nerves, and lymphatics or lacteals, hence it permits vascular and
nervous communications with the organ attached to it. The free portion
of the small intestine is attached to the free margin of the mesentery.


       THE RELATIONS OF THE VISCERAL ORGANS OF THE DOMESTIC FOWL

[Illustration:

  FIG. 40.—Transverse section through the body of a hen through 14, Fig.
    34. _R_, Right side. _L_, Left side. 1, Spinal cord. 2, Esophagus.
    3, Trachea near inferior larynx. 4, Lungs. 5, Pectoral muscles.
]

Figure 33 shows a fowl with the left abdominal wall and the left
thoracic wall removed. No. 1 in this figure shows the base of the heart
in front of the left lobe of the liver. Above the liver is the
proventriculus; above this, the diaphragm; and above the diaphragm and
the base of the heart the left lung occupying the superior part of the
thoracic cavity, and that there is no distinct pleural sac, as in
mammals but that the lung pushes out between the ribs, thus pressing
against the ribs on the inner and the lateral sides. The gizzard is back
of the liver, to the left side of the abdominal cavity, and beneath and
in front of the duodenal loop. The small intestine from this side is
above the gizzard. Supero-anterior to the gizzard is the blind end of
the cæcum. The pancreas is within the duodenal loop.

[Illustration:

  FIG. 41.—Transverse section through the body of a hen at 12, Fig. 33.
    _R_, Right side. _L_, Left side. 1, Spinal cord. 2, Esophagus. 3,
    Inferior larynx. 4, Base of the heart. 5, Aorta. 6, Vena cava. 7,
    Lungs. 8, Skin. 9, Pectoral muscles.
]

Figure 34 shows the viscera from the right side after the removal of the
right abdominal and the right thoracic wall. The base of the heart is in
front of the right lobe of the liver. Above these the right lung
occupies the upper part of the thoracic cavity as in the preceding
illustration. Just back of this is the anterior lobe of the kidney. The
gall-bladder is observed at No. 9 on the right lobe of the liver. Just
inferior to a longitudinal central line is the duodenal loop, between
the limbs of which is seen the pancreas. Above this loop the cæca are
located. The gizzard is not visible from the right side; on this side
posterior to the liver is the small intestine. Superior to this at No. 7
the rectum.

The relative position of the visceral organs in the median line is
observed in Fig. 35. No. 1 of this figure shows the stump of the first
portion of the esophagus, and No. 2, the left wall of the crop.
Following this, and located just below the vertebræ is the second
portion of the esophagus. The major portion of the crop is located on
the right side.

[Illustration:

  FIG. 42.—Transverse section through the body of a hen at 11, Fig. 33.
    _R_, Right side. _L_, Left side. 1, Spinal cord. 2, Vertebra. 3,
    Spinous process of vertebra. 4, Lungs. 5, Esophagus. 6, Pericardial
    sac. 7, Sectioned surface of heart. 8, Auricle of heart. 9, Blood
    clot in right auricle. 10, Section of sternum. 11, Pectoral muscles.
]

It will be noted that the second portion of the esophagus passes over
the base of the heart and the superior part of the liver, and then
terminates in the proventriculus. The proventriculus extends downward
and empties into the gizzard. This organ lies antero-laterally to the
gizzard, supero-posterior to the liver, and to the left of the spleen.
The spleen lies in a triangle formed by the liver, the proventriculus,
and the gizzard. The heart is noted to lie supero-anterior to the liver,
and between the anterior portion of the fissure formed by the right and
the left lobe. The ovary is located back of the diaphragm at the
anterior end of the kidney and below the inferior surface of the bodies
of the vertebræ. The bulk of the floating portion of the small intestine
is located above the gizzard.

[Illustration:

  FIG. 43.—Transverse section through the body of a hen at 13, Fig. 34.
    _R_, Right side. _L_, Left side. 1, Spinal cord. 2, Body of
    vertebra. 3, Superior spinous process of vertebra. 4, Lungs. 5,
    Esophagus. 6, Heart. 7, Right and left lobes of liver. 8, Sternum.
    9, Skin. 10, Pectoral muscles.
]

A transverse anterior section of a normal laying hen is shown in Fig.
39, the section being made at 15 of Fig. 34. At this point the esophagus
lies centrally and above the trachea. Figure 40 shows a transverse
anterior section through the thoracic region at 14 of Fig. 34. At this
point the esophagus is slightly to the right of and is superior to the
trachea. At this level the apex of the lung is sectioned. This is in the
region of the cervical air-sac. Figure 41 shows a posterior section at
12 of Fig. 33. The esophagus here is above and to the right of the
inferior larynx, and directly below and between the lungs. The inferior
larynx is above the base of the heart.

Figure 42 shows a transverse anterior section made at 11 of Fig. 33. It
shows that at this level the esophagus is centrally located and passes
over the base of the heart. The heart occupies the lower portion of the
thorax and the lungs the upper. Figure 43 shows a photograph of a
transverse anterior section of the body made at 13 of Fig. 34. At this
level the apex of the heart lies within the anterior fissure of the
liver. The sectioned portion of the heart shows the lower portion of the
ventricle.

[Illustration:

  FIG. 44.—Transverse section through the body of a hen at 12, Fig. 34.
    _R_, Right side. _L_, Left side. 1, Spinal cord. 2, Articular
    surface of vertebral segment. 3, End of rib. 4, Lungs. 5,
    Proventriculus. 6, Liver showing Glisson’s capsule. 7, Sternum. 8,
    Pectoral muscles. 9, Skin.
]

[Illustration:

  FIG. 45.—Transverse section through the body of a hen at 10, Fig. 33.
    _R_, Right side. _L_, Left side. 1, Spinal cord. 2, Body of
    vertebra. 3, Lungs. 4, Ova. 5, Proventriculus. 6, Liver. 7, Sternum.
    8, Skin. 9, Pectoral muscles.
]

In this figure the lungs show, on the sectioned surface, the ends of
some of the larger bronchi. The esophagus is located above the heart.
Showing the relations of the visceral organs back of the heart girdle,
photograph number 44, gives an anterior section made at 12, Fig. 33. The
lungs are spread out occupying the posterior thoracic region and below
at No. 10 is the diaphragm. The diaphragm does not appear to have that
rigidity and firmness of position as in mammals. It is rather
rudimentary. Below the left lung and above the left lobe of the liver is
the proventriculus. Note that the viscus is empty and that the mucous
membrane is thrown into folds. At this point the liver occupies much of
the abdominal cavity. Figure 45 is a view of an anterior section made at
10, Fig. 33. In this section the lungs are decreasing in caliber. The
liver occupies much of the space in the lower right abdominal quadrant,
and above and to the right is the ovary with many of the ova developing
yolks. Below No. 4 which is a developing yolk, is the proventriculus.
Figure 46 is a view of an anterior section made at 9, Fig. 33. At this
level are shown sectioned surfaces of the kidneys, which lie on either
side of the spinal column. Below the spinal column and occupying the
left upper quadrant is the ovary containing ova in the process of
developing yolks. To the right is the sectioned surface of one of the
cæca and below this and on the right side is the sectioned ends of many
of the loops of the floating portion of the small intestine. Occupying
the left lower quadrant is the sectioned surface of the gizzard and on
the abdominal floor and to the right of the gizzard, the posterior end
of the right lobe of the liver.

[Illustration:

  FIG. 46.—A transverse section through the body of a hen at 9, Fig. 33.
    _R_, Right side. _L_, Left side. 1, Spinal cord. 2, Vertebra. 3,
    Kidneys. 4, Ovary. 5, Cæcum. 6, Small intestine. 7, Gizzard. 8,
    Right lobe of liver. 9, Skin. 10, Pectoral muscles.
]


         THE RELATIONS OF THE VISCERAL ORGANS OF THE BABY CHICK

There is approximately 47 per cent. of the yolk retained in the
abdominal yolk sac of the baby chick at hatching. Figure 47 shows a
photograph of a longitudinal section through a baby chick. This figure
shows all the posterior portion of the abdominal cavity occupied with
abdominal yolk. The abdominal viscera are pushed forward, and as the
yolk is gradually absorbed the visceral organs gradually occupy their
normal position.

[Illustration:

  FIG. 47.—An antero-posterior section through the body of a baby chick
    just hatched. 1, Abdominal yolk sac. 2, Gizzard. 3, Liver. 4, Heart.
    5, Intestines. 6, Spinal cord. 7, Cerebrum. 8, Cerebellum. 9, Fat in
    the post-occipital region. 10, The thymus gland.
]

[Illustration:

  FIG. 48.—Transverse sections of the body of a baby chick at hatching.
    _R_, Right side. _L_, Left side.

  _A._ A transverse section at _A_, Fig. 50. 1, Spinal cord. 2,
    Esophagus. 3, Entrance to thorax. 4, Stubs of the wings.

  _B._ A transverse section at _B_, Fig. 50. 1, Spinal cord. 2,
    Esophagus. 3, Lungs. 4, Heart.

  _C._ A transverse section through the body at _C_, Fig. 50. 1, Spinal
    cord. 2, Lungs. 3, Esophagus. 4, Liver. 5, Heart.

  _D._ A transverse section at _D_, Fig. 50. 1, Spinal cord. 2,
    Proventriculus. 3, Liver. 4, Gizzard. 5, Intestine. 6, Kidneys. 7,
    Gall-bladder.
]

[Illustration:

  FIG. 49.—Transverse section through the body of a baby chick.

  _E_ at _E_, Fig. 50. 1, Spinal cord. 2, Kidneys. 3, Gizzard. 4,
    Intestines. 5, Unabsorbed yolk. 6, Stubs of legs.

  _F._ A section at _F_, Fig. 50. 1, Spinal cord. 2, Kidneys. 3,
    Intestine. 4, Unabsorbed yolk.

  _G._ A section at _G_, Fig. 50. 1, Anus. 2, Umbilicus.
]

A section through this body Fig. 47 at _A_ is shown in Fig. 48, _A_. At
this point the esophagus appears below the vertebral column. Figure 48,
_B_, a section through the body at Fig. 47, _B_, shows the apex of the
lungs. In a median line and below the lungs is the esophagus. Note the
mucous membrane thrown into folds. Here the heart is sectioned, showing
both auricles and both ventricles. This is a view looking forward.
Figure 48, _C_, is a view of a posterior section made at Fig. 47, _C_.
It shows the same relations of the esophagus and lungs, but shows at
this level both the right and the left lobe of the liver. Between these
lobes we note the sectioned apex of the heart. Figure 48, _D_ shows a
posterior section at Fig. 47, _D_. At this level the kidneys are above
and infero-laterally to the spinal column. The intestines are below the
kidneys; and on the left side, between the kidneys and left lobe of the
liver, and near the abdominal wall, is the proventriculus. Occupying the
major portion of the inferior abdominal cavity are the right and the
left lobe of the liver, and between these the anterior border of the
gizzard. Note the gizzard sitting at an angle inclining toward the left
side. Figure 49, _E_ shows a section at Fig. 47, _E_. Here the gizzard
occupies the left lower abdominal quadrant. To the right are the
intestines; and directly above the gizzard is a small portion of the
anterior end of the abdominal yolk sac. Infero-laterally are the
kidneys. Figure 49, _F_, shows the kidneys similarly located as in the
preceding; and just below is the rectum suspended by the mesentery. The
rest of the cavity is occupied by the abdominal yolk.




                         THE URO-GENITAL SYSTEM


The uro-genital apparatus, or apparatus uro-genitalis, consists of two
groups of organs: the urinary and the genital. The former elaborate and
remove the chief excretory fluid, the urine; and the latter serve for
the formation, development, and expulsion of the products of the
reproductive glands.


              THE URINARY APPARATUS (Fig. 50 and Fig. 51).

The urinary apparatus of the bird consists of two kidneys, from each of
which a ureter extends and empties into the cloaca.

=The Kidneys.= _Location._—The kidneys are located in excavations in the
pelvic roof. They are related internally with the posterior aorta and
vena cava, supero-internally with the lumbo-sacral vertebræ and
superiorly and supero-externally with the ilium. The abdominal visceral
organs lie below the kidneys. The kidneys are external to or above the
peritoneum.

_Shape._—In the fowl of average size the kidneys are 2½ inches long and
are made up of three irregular lobes. The anterior lobe is usually the
largest and the middle the smallest. The anterior border of the first
lobe is located opposite the last true dorsal articulation. The anterior
lobe is called the anterior pelvic or ilio-lumbar lobe, the middle the
middle pelvic or ilio-sacral lobe, and the posterior the posterior
pelvic lobe.

_Structure._—The whole kidney has a fine transparent covering. The dark,
brownish-red parenchyme can be seen through this membrane. It has a
blood vascular system and a urinary tubular system. The larger arteries,
the veins, and the nerves pass between the lobules, and the smaller
vessels between the tubules. These form fine network or plexuses. The
lymphatic vessels are very few, and are mainly found on the surface. The
kidneys are pierced in their posterior third by the external iliac
artery and at about its middle by the venous branches forming the
posterior vena cava.

The lobes are made up of _lobules_, which are plainly perceptible from
the external surface. Each lobule is apparently a unit within itself. It
receives its blood supply from small branches of the renal artery and is
made up of a cortical or peripheral portion which contains the
glomerules (Fig. 52, _A_) and a medullary portion, which is made up of
tubules, or urinary canals, arteries, veins, and nerves.

[Illustration:

  FIG. 50.—Photograph showing spinal cord and relative positions of the
    kidney, lung and heart. 1, Heart. 2, Lung. Note the indentations
    made by the ribs. 3, The anterior, middle and posterior lobes of the
    kidney. The lobules are plainly visible. 4, The lumbo-sacral segment
    of the spinal cord. 5, Terminal cord filament. 6, The cervico-dorsal
    segment of the spinal cord. 7, The brachial nerve plexus. 8 and 9,
    The lumbo-sacral plexus. 8, The ischiadic nerve. 9, The lumbar
    nerves.
]

The _urinary canals_ are divided into two kinds, namely, the outer and
the inner tubular systems. The outer canals, called the _tubulæ
uriniferi corticalis_, are very small in caliber and are located in the
lobules. The renal artery (Fig. 53, No. _B_, 3) breaking up into
arterioles in the kidney, and finally reaching the cortical portion of
the lobules, form capillary plexuses in the shape of minute spheres,
which are the glomerules (Fig. 53, No. _C_, 3 and _B_, 5). Around each
glomerule there is formed a capsule called _Bowman’s capsule_, which is
the beginning of the uriniferous tubule. This entire mass is called the
_Malpighian body_, or _renal corpuscle_. This capsule then extends as
the urinary, or secreting tubule, being at first constricted, then
convoluted, and terminates into a second portion, the _descending limb
of Henle_. This portion of the tubule becomes constricted. It then forms
the loop of Henle and ascends as the second portion, or second limb of
Henle, which is again of greater diameter. The top of the secreting
tubule is slightly wavy and empties into the collecting tubule along
with many others. These collecting tubules in turn merge into large
tubules which finally empty into the ureter (Fig. 53, No. 14). These
collective bundles correspond to the pyramids of the kidneys of mammals.

[Illustration:

  FIG. 51.—The kidneys. 1_a_, The posterior. 1_b_, the middle and 1_c_,
    the anterior lobes of the kidney. 2, The posterior aorta. 3, The
    external iliac or crural artery. 4, The ischiadic artery. 5, The
    sacralis media artery. 6, The ureter which empties into the cloaca
    at 7. 8, The external iliac vein. 9, The internal iliac vein. 10,
    The iliacus communis.
]

[Illustration:

  FIG. 52.

  _A._ Photomicrograph of a section of a kidney showing three lobules.
    1, Cortical portion of lobule showing glomeruli. 2, The central or
    medullary portion of the lobule. 3, The outer surface of the kidney.

  _B._ Salts from the urine of a hen. 1, Uric acid crystals. 2. Sodium
    urate crystals.
]

[Illustration:

  FIG. 53.—The renal structure.

  _A._ 1, Capillary blood-vessel. 2, Descending limb of Henle. 3,
    Collecting tubule. 4, Ascending limb of Henle.

  _B._ 1, Branch of renal artery. 2, The descending or medullary branch.
    3, The ascending branch. 4, The arteriole taking part in the
    formation of the glomerule. 5, The glomerule. 6, Bowman’s capsule.
    7, Blood-vessel extending from the glomerule. 8, The vein of the
    medullary part of the lobule. 9, The neck. 10, The convoluted
    tubule. 11, The descending limb of Henle. 12, Henle’s loop. 13, The
    ascending loop of Henle. 14, The collecting tubule.

  _C._ 1, Section through a convoluted tubule. 2, Bowman’s capsule. 3,
    The glomerule.
]

The neck of the uriniferous tubule as it emerges from Bowman’s capsule
is short and narrow and is lined with a few cuboidal cells. Toward the
glomerular end the cells are of a transitional form gradually merging
into the flat squamous type peculiar to Bowman’s capsule. The first
convoluted tubule is lined with irregular cuboidal or pyramidal
epithelial cells. The descending limb of Henle’s loop is narrow and is
lined with a simple layer of flat epithelial cells. In the loop the
epithelium changes from the flat type in the descending limb to the
cuboidal in the ascending limb. The ascending limb of Henle’s loop again
becomes broader and is lined with low cuboidal cells. The second
convoluted, or tortuous, tubule is lined with low cuboidal cells as are
also the collecting tubules. The collecting tubules originate from every
part of the internal substance of the lobules, and extending to the
gyrations, uniting in the pinniform structure and traversing to the
margin of the lobules, following along the uneven surface,
infero-laterally and toward the median body line, finally empty into the
ureter.

There are many arterial branches given off from the arteria renalis. The
arteries which supply the kidneys are given off from the posterior aorta
and ischiadic artery. As soon as these arteries enter the kidney they
break up into two systems. One system supplies the kidney substance with
nourishment in the form of nutrient blood; the second system supplies
the glomerules with what may be considered functional blood (Gadow). The
second system of arteries branches into the small arteria
interlobularis, which pass between the lobules of the kidneys where they
give off side branches which penetrate the cortical portion of the
lobules and form the capillary plexus, the glomerule.

The arteriole that enters into the structure of the glomerule is lined
with endothelial cells and is surrounded by a few muscle fibers and a
fine network of connective tissue. The vessel that carries the blood
away is similarly constructed.

_Function._—In the glomerules the liquid portion of the urine is
filtered out of the blood, which urine flows through the uriniferous
tubules and passes from the kidney through the ureter. In the cubical
cells are extracted the solid portions of the urine which also pass
through the tubules with the liquid. The urinary secretion, as found in
the ureter, does not contain much liquid, but, on the contrary, is made
up of a pasty material consisting of salts which are, for the most part,
uric acid crystals and sodium urate (Fig. 52, _B_). This material
becomes hard, like cement, soon after being exposed to the atmosphere.
This secretion may be noted as a whitish pasty material on the outer
parts of the feces, or droppings, voided by the birds.

=The Ureter.= _Location._—The ureter extends along the inferior surface
of the kidney. It has its origin near the anterior extremity of the
kidney, and passing posteriorly the entire length of the kidney receives
tributary collecting tubules, and terminates in the upper wall of the
cloaca in the urodeumal portion.

_Shape._—The ureter gradually enlarges in diameter until it reaches the
posterior border of the kidney, and then maintains about the same
caliber throughout the rest of its course.

_Structure._—The ureter wall is made up of three coats as follows:
mucous, muscular and fibrous.

_Function._—The ureters serve as a passage way for the urine from the
kidneys to the cloaca.


                  THE MALE GENERATIVE ORGANS (Fig. 54)

The male generative organs in the fowl consist of two testicles and an
excretory apparatus, the vas deferens, for each.

=The Testicles.= _Location._—The testicles are located in the sublumbar
region of the abdominal cavity, behind the lungs, below the anterior
extremity of the kidneys, and opposite the last three ribs.

[Illustration:

  FIG. 54.—The pelvic organs of a cockerel. _A_, Testes. _B_, Rectum.
    _C_, Cloaca. _D_, Vas deferens. _E_, Kidney. _F_, Adrenal gland.
    _G_, Lungs. _H_, Ureter.
]

_Shape._—The testicles are ellipsoid in shape; their size varies with
the different species of birds. The two in the same bird are usually of
the same size, though one testicle may be slightly larger than the
other. In a summary of a large number of weights of the testicles of ten
months old cockerels, the average weight was 0.021 pound each. The
average measurements were 2 inches in the major diameter and 1 inch in
the minor diameter. In the cockerel before sexual maturity, which is
denoted by the male bird’s crowing, the testicles are very small. They
resemble, in shape, a navy bean and are yellowish-white in color.

_Structure._—The testicle is surrounded by a thin fibrous capsule,
which, in the mature cock, is very vascular. This capsule sends into the
interior of the gland, septa which form the framework, or supporting
structure. This framework forms the spaces in which are located the
glandular substance. The glandular portion consists of the _tubuli
seminiferi_, which are lined with cubical cells. The framework
supporting these tubules gives passage to arterial branches of the
spermatic artery, which furnish an abundant blood supply; the framework
also supports the veins returning the blood from the testicle. The
seminiferous tubules end in blind extremities in the epididymus or
globus minor, and unite in the seminiferous canals. All arteries, veins,
lymphatics, and seminiferous tubules enter or leave through the globus
minor at the attached portion of the testicle. The _epididymis_ is made
up largely of convoluted tubules which are the continuation of the
secreting tubules of the globus major. The walls of the tubules of the
globus minor become thicker and are provided with smooth muscle cells in
addition to the connective tissue and endothelial lining. The convoluted
tubules empty into the vas deferens. The epididymus is covered by the
fibrous capsule; which corresponds to the tunica albuginea of mammals
and may be considered as a reflection or modification of the visceral
peritoneum.

The substance of the testicle is very soft; in fact, it may be said to
be of the consistency of encephaloid material. It is made up of
secreting tubules in which are found the spermatozoa; it also contains
cells which produce an internal secretion, or hormone. There is also
produced some fluid in which the spermatozoa float, the whole material
manufactured constituting the semen.

The _spermatozoa_ of the fowl are provided with long cylindrical bodies,
which may be straight or wavy (Fig. 55, _A_). The body of the
spermatozoon is obtuse anteriorly, and posteriorly, tapers into a
filimentary tail, or flagellum, of varying length, by the aid of which
the spermatozoon moves about in the fluid.

The histological structure of the testicles of the baby chick at
hatching is approximately one-half white fibrous connective tissue. The
seminal tubules are small and widely distributed among the connective
tissue. The cells of these tubules possess rather large nuclei, round in
shape, with linin network and chromatin granules, typical of resting
germ cells. As the bird develops the testicles grow, the seminal tubules
become larger, and the amount of connective tissue correspondingly less.

[Illustration:

  FIG. 55.

  _A._ Spermatozoa of a cock. _a_, The spermatozoa. _b_, The head. _c_,
    The tail.

  _B._ The oviduct of a hen removed. _A_, The oviduct. _B_, The superior
    ligament. _C_, The inferior ligament. Note the oviduct thrown in
    folds and the anastomosing blood-vessels.
]

In addition to the tubules, the spermatogenic cells, and the connective
tissue, there is also in the testicles more or less fat. There is a
small amount of connective tissue between the seminiferous tubules, in
which locations there are also clusters of polyhedral cells, with round
nuclei, others are the interstitial cells.

=The Vas Deferens= (Fig. 54, _D_). _Location and Shape._—Extending from
the epididymus, is the vas deferens which runs backward on the
infero-internal surface of the kidney and to the outside of the ureter.
It is very tortuous passing on the infero-lateral surface of the kidney
in company with the ureter and becoming somewhat expanded posteriorly it
terminates in the upper wall of the cloaca in a rather small papilla
located in the uro-genital portion of the cloaca anterior to the mouth
of the ureter. This papilla is the organ of copulation and in ducks is
very large, and spirally elongated, and retractile forming a kind of
penis. The papilla is traversed by a furrow on the upper surface through
which the semen flows.

_Structure._—The vas deferens is covered and supported by the
peritoneum. Its wall is made up of a fibrous structure in which may be
found smooth muscle fibers. The wall does not possess glands. It is
lined with columnar epithelium. The posterior end is expanded and
terminates into a papilla. The base of the papilla is surrounded by a
plexus of arteries and veins, which serve as an erectile organ during
the venereal orgasm, when the fossa of the turgid papilla is everted,
and the semen brought into contact with the similarly everted orifice of
the oviduct of the female, along which the spermatozoa pass by
undulatory movements of their ciliary appendage, or tail.


                 THE FEMALE GENERATIVE ORGANS (Fig. 56)

The female generative organs consist of one ovary and an oviduct.

_Location._—The ovary is located similarly to the testicles of the male
bird, in the sublumbar region of the abdominal cavity, just at the
anterior end of the kidneys, posterior to the lungs, and slightly to the
left of the center.

_Shape._—In the pullet the ovarian mass appears somewhat like a bunch of
grapes, being made up of from 3500 to 4500 small, whitish spheres, which
represent the undeveloped ova, and which in the active state are
developed, one by one, into yolks with their blastoderms. From the
blastoderm the fetus may later be developed. In the active ovary of the
laying hen the ovarian mass is of considerable size, as it contains ova
in different stages of development. Only one ovum is completely
developed at a time, though occasionally there may be only a few hours
between the maturity of successive ova. The ova receives nourishment
from the blood-vessels of the capsule, which vessels are branches of the
ovarian artery.

[Illustration:

  FIG. 56.—Functionating female generative organs of a hen. 1, Ova in
    process of formation of yolk. 2, Stigmal line at which point the
    capsule ruptures when ovum is mature. 3, The funnel end of the
    oviduct. 4, The oviduct torn loose and laid to one side, the
    albumin-secreting portion. 5, The shell membrane secreting portion.
    6, The albumin. 7, The yolk. 8, The shell-secreting portion. 9, The
    cloaca. 10, The rectum.
]

_Structure._—The ovary contains very vascular cellulofibrous tissue. The
ovum as it develops is attached to the ovarian body by means of a
delicate white fibrous pedicle. When the yolk is mature it escapes from
the enveloping fibrous capsule by a cleavage of the capsule. The
cleavage line is called the _stigmen_ (Fig. 56, No. 2). The yolk is
surrounded by a very delicate membrane called the _vitelline membrane_.
The empty sac now shrinks and finally disappears.

=The Egg.=—The principal divisions of the egg are the yolk, the albumin
outside of the yolk content, the shell membranes and the shell (Fig.
58). As stated, the _yolk_ is formed in the ovary, leaving the other
three portions to be formed in the oviduct.

[Illustration:

  FIG. 57.—Section through the ovary of the hen. _a_, The ova. _d_, An
    ovum beginning to receive deposits of yolk material. _c_, Ova
    farther advanced in yolk formation.
]

The _albumin_ may be subdivided into, first, a thin layer of albumin
lying close around the yolk; second, a thick layer of albumin lying at
the outer periphery; and third, a modification of the albumin called the
chalazæ. The chalazæ are twisted, dense cord-like structures at either
pole of the yolk, one end of which is adherent to the vitelline membrane
and the other to the inner membrane surrounding the albumin. The chalazæ
thus act as stays to this structure, which is carrying a delicate
burden, the blastoderm.

The _shell membrane_ consists of two layers, an inner delicate, and an
outer thicker layer. When the egg is just laid these two membranes are
in all parts closely adherent to each other, and the egg content
completely fills the shell cavity. As soon as the content cools there is
a slight contraction; the two shell membranes separate at the large end
of the egg, forming an air cell which gradually enlarges as the
evaporation of liquid through the pores of the shell takes place.

[Illustration:

  FIG. 58.—A diagram of the parts of the egg. _a_, The blastoderm. _b_,
    The shell. _c_, The outer shell membrane. _d_, The inner shell
    membrane. _e_, The air-sac at the large end of the egg. _f_, The
    albumin. _g_, The chalaza. _h_, The yellow layers of yolk. _i_, The
    white layers of yolk. _k_, The flask-shaped portion of white yolk.
    _l_, The vitelline membrane.
]

The shell consists of several layers. Three are easily distinguishable:
first, an inner mammillary layer, consisting of minute conical deposits
of calcareous material; second, a middle spongy layer, composed of a
thick network of fibers; third, an outer delicate, cuticle-like
structure. In certain breeds of poultry a pigment may be added; for
example, in ducks a pea green, in turkeys a spotted brownish material,
and in fowls pink and various shades of brown. The egg shell is porous
to admit the free exchange of air during the process of incubation.

An average sized hen egg weighs about 2 ounces, of which 11 per cent. is
shell, 32 per cent. yolk, and 57 per cent. white. The principal chemical
constituents of the egg are as follows: ash, or mineral matter, 9 per
cent.; fat, or hydrocarbon, 9.3 per cent.; proteids, or nitrogenous
matter, 11.9 per cent.; and water, 65.5 per cent. There is apparently no
constant proportion of weight between the yolk and albumin. There is
also a variation in the weight of the shell due to its variation in
thickness.

In an examination of ten eggs of average size, the yolk constituted 31
per cent. of the total weight of the egg.

The following is the result of the analysis of twelve eggs of average
size. This analysis included the shell and all other parts taken
together.[6]

Footnote 6:

  The analysis was made by D. M. McCarty, chemist, Animal Industry
  Division, North Carolina Experiment Station.

                      Moisture    64.25 per cent.
                      Dry matter  35.75 per cent.
                                 ————————————————
                                 100.00 per cent.

                      Parts per hundred including
                                 shell

                      Protein             10.2500
                      Fat                 10.6200
                      Phosphorus            .3020
                      Calcium               .6080
                      Magnesium             .0985
                      Iron                  .0103
                      Sulphur               .3950
                      Chlorine              .1506
                      Potassium             .0103
                      Sodium                .2000

=The Oviduct.=—The three separate and distinct portions of the egg,
albumin, shell membranes, and the shell, are constructed in different
parts of the oviduct.

_Location._—The oviduct of the hen extends along the left side of the
bodies of the vertebræ, and the roof of the pelvic cavity and lies
dorsal to the abdominal air-sac. It extends from the posterior border of
the ovary and empties into the cloaca (Fig. 56, No. 3 and 8) through a
transverse slit.

_Shape._—In a well-developed Plymouth Rock pullet, but one whose
reproductive organs have never become active, the oviduct is about 4½
inches long; in the fully developed and active state it is from 18 to 20
inches long, and in a collapsed state about ½ inch in diameter. It is
held in position by two ligaments, a dorsal and a ventral (Fig. 55, _B_)
to be described later. The oviduct is tortuous in its course, forming
three principle convolutions before reaching the cloaca, and like the
ovarian mass, in its active state, pushes the abdominal viscera downward
and toward the right side.

_Structure._—The oviduct consists of three coats: first, the serous,
located on the outside, which is a reflection of the peritoneum; second,
the muscular middle tunic; third, the mucous coat, which in a resting
state is thrown into folds.

[Illustration:

  FIG. 59.—The active oviduct of a hen laid open. 1, The ovary. 2, The
    funnel. 3, The albumin-secreting portion. 4, The isthmus. 5, The
    shell=gland portion. 6, The vagina. 7, The superior ligament. 8, The
    inferior ligament.
]

=Parts of the Oviduct.=—The parts of the oviduct are as follows: the
funnel, the albumin-secreting portion, the isthmus, the shell-gland
portion, or uterus, and the vagina (Fig. 59).

[Illustration:

  FIG. 60.—The mucous lining of the oviduct.

  _A._ Transverse section of the oviduct wall in the region of the neck
    of the funnel showing primary and secondary folding of the
    epithelium (after Surface).

  _B._ Showing the type of gland cells of the funnel region.

  _C._ Transverse section through the wall of the uterus showing the
    deep folds.

  _D._ Section from the albumin-secreting portion showing the opening of
    a tubular gland and also showing the character of the cells.
]

The _funnel_ is the trumpet-shaped portion, the ostium tubæ abdominale,
whose mouth or fimbriated opening faces the ovary, and lies ventrally to
receive the ovum, or yolk, as it is discharged from the ovary. Its thin
wall, expanded in the anterior portion, is provided with fimbriæ-like
projections. This funnel-shaped portion soon converges to form a
constricted portion. This portion of the active oviduct is from 3 to 4
centimeters long. The mucous membrane occurs in folds forming low
longitudinal spiral ridges (Fig. 60, _A_). The fimbriæ are continuous
with the dorsal and the ventral ligament of the oviduct; and from this
point, where the ridges of the mucous membrane are almost nil, they
gradually increase in height as they extend down the tube. These ridges
are continued in those of the second, or albumin-secreting portion (Fig.
60, _D_). At this point they increase in height very rapidly. Here the
bundles of muscular fibers of the middle coat are thin and distributed
among bundles of connective tissue. The muscular fibers consist of two
layers, an outer longitudinal and an inner circular. At places in this
portion the inner bundles may be noted to extend longitudinally. In
embryological development the epithelial layer has an origin different
from the outer layers of the oviduct. In the fetal development the
Müllerian duct arises as a thickening along the Wolffian body just
ventral to the gonad. This Müllerian duct is at first a solid cord of
cells. It later develops a lumen, and grows posteriorly until it
connects with the cloaca. At the time of this posterior growth,
mesenchyme cells migrate in from the surrounding tissue and form a layer
about the duct. From this layer of mesenchyme cells there are developed
the outer layers of the oviduct, which layers later develop the muscular
structure and the connective tissue. The epithelium and its derivatives,
which represent the glandular structures, are formed from the walls of
the old Müllerian duct. Thus the two sets of tissues, having different
origins, likewise have different functions. The epithelium is concerned
entirely with secretion, and the derivatives of the mesenchyme are
concerned with supporting and muscular function.

[Illustration:

  FIG. 60. _A._—The mucous lining of the oviduct.

  _E._ Section of the epithelium from the vagina showing unicellular
    glands.

  _F._ A section from the isthmus showing opening of a tubule.
]

To summarize, six layers of tissue occur in the funnel region, namely,
an outer serous covering, an outer longitudinal muscular layer, a layer
of connective tissue, an inner circular layer, a second layer of
connective tissue, and an inner mucous layer. The mucous layer is made
up of glands, as follows. The unicellular glands occur between the
ciliated cells of the epithelium. These glands are found only in the
posterior half of this division of the oviduct. The glandular grooves
are made up of an accumulation of gland cells at the bottom of the
grooves between the secondary folds of the epithelium. These are found
in all parts of this division except the extreme posterior part. In the
posterior part we find the third type of glands, the tubular variety.

The second division of the oviduct, as stated above, is the
_albumin-secreting portion_. The funnel division gradually merges into
the second portion. These two portions are distinguishable from each
other. The walls of the albumin-secreting portion are much thicker and
the longitudinal ridges are higher. This section is the longest of the
five divisions, measuring from 40 to 42 centimeters in length, or more
than half the length of the oviduct. The albumin division terminates
rather abruptly into the third division, the isthmus (Fig. 59, _A_).

It is probable that the secretion of albumin is not confined to the
cells of the second division; yet we are safe in saying that the major
portion is formed here. The folds of mucous membrane in this division
are thicker and higher than in the funnel, due to their containing cells
of the high columnar type, and to the fuller development of the glands
which are of the tubular variety. The muscular layer is heavier, and
therefore the muscular power to force along the tubes’ contents is
greater. In the formation of the mucous folds we find, in transverse
sections, that the central core is made up of connective tissue which
carries blood-vessels and nerve filaments, as in other similar glandular
structure. The epithelium contains glandular cells of two varieties,
namely, the ciliated, columnar variety, and the unicellular, goblet
variety (Fig. 36, No. _B_, 2). These two kinds of glandular cells are
rather evenly distributed throughout the epithelium of this section of
the oviduct. The unicellular gland cells are more numerous at the mouths
of the ducts leading from the tubular glands. The nuclei of the ciliated
cells are oval and lie near the middle of the cells or a trifle toward
the base from the middle. The protoplasm of the cells is finely
granular. Strong cilia in considerable number surmount each cell. In
some cases the goblet or mucous cells have pushed apart the ciliated
cells, and their prolongations extend farther than the surface of the
ciliated cells. The nuclei of the goblet cells are round, and lie nearer
the proximal end than those of the ciliated cells.

The third division of the oviduct, the _isthmus_, continues from the
albumin-secreting portion and terminates in the expanded portion called
by some anatomists, the uterus. Toward the posterior end of the
albumin-secreting portion the longitudinal folds of mucous membrane
become lower, making, at the juncture of this and the isthmus, a clear
fine of demarcation. For a distance of 2 or 3 centimeters the folds are
low, after which they gradually become higher, but never reach the
height or thickness of those in the albumin-secreting portion.

The clear-cut line between the albumin-secreting portion and the isthmus
is partly due to a zone in which the long tubular glands are lacking.
The core of the folds of mucous membrane in this zone contain much more
connective tissue. The cells are both ciliated and unicellular. The rest
of the histological structure of the isthmus is the same as that of the
albumin-secreting portion.

The function of the isthmus is to secrete, or to form, the shell
membrane, the membrana testacea.

The fourth division of the oviduct is the _uterus_, or the shell-gland
portion (Fig. 60, _C_). There is no clear line of demarcation between
the isthmus and shell-gland portion, the walls gradually expanding. In
this region the folds of mucous membrane become leaf-like and of
considerable length, extending into the lumen, thus affording a greater
cellular surface. The same coats of the duct are present here as in
other parts; but the outer longitudinal muscular layer is thicker and
possesses more strength. The quantity of connective tissue is about the
same. The glands are of a tubular type and the same two varieties of
epithelial cells are found here as elsewhere, namely, the ciliated high
columnar and the unicellular mucous variety.

In the active glandular cells of the shell-forming region the nuclei are
small, dark staining, and lie toward the center of the cell. The
chromatin granules and nucleoli take on a comparatively deep basic
stain, but they do not show the intense stain found in the albumin and
the isthmus region. The cytoplasm of the uterine tubular glands does not
present as heavy a granular appearance as that of the albumin portion.
These cells are diffusely granular, the granules appearing of one size
and taking the stain faintly. The function of this portion is to
secrete, or form, the hard calcareous covering which has been described
at the beginning of this section.

The fifth division of the oviduct is the _vagina_. There is located, at
the juncture of the shell-gland portion with the vagina, a strong
sphincter muscle. The vagina is that constricted portion of the oviduct
extending from this muscle to the cloaca. The mucous membrane forms low
narrow folds with secondary folds, which appear continuous with those of
the shell-gland portion. The core of these folds is composed of
connective tissue. The vagina in the hen of average size measures from
12 to 13 centimeters long (Surface). The inner or circular muscular
layer is well developed; it is much thicker than in any other part of
the oviduct. This extra development gives the power necessary to
successfully expel the egg. The outer longitudinal layer is not so well
developed; its bundles are scattered throughout the connective-tissue
layers. The egg is caused to move along in the oviduct by a successive
series of contractions of the circular muscular fibers posterior to it.
There are no tubular glands in this portion, but a simple layer of high
ciliated columnar epithelium, and some goblet, or mucous cells. The
cells on the surface generally are long and slender; in the grooves
between the mucous folds the cells are shortest, reaching their greatest
length at the tops of the folds.

The function of the vagina is the secretion, or formation, of the outer
shell cuticle commonly called the bloom, and also in certain breeds, as
indicated above, the tint.

The cloaca furnishes a passage way from the vagina to the external world
by way of the anus. The walls of the cloaca contain glands.

=The Ligaments of the Oviduct.=—It is held in position by two ligaments,
one dorsal and one ventral. The _dorsal ligament_ of the oviduct is
formed by a double layer of peritoneum with a very small amount of
connective tissue interposed. The peritoneum is also reflected over the
oviduct. The ventral ligament of the oviduct is narrower than the
dorsal, but is similarly constructed. Both ligaments are rather
veil-like in appearance. During the first four or five months of the
growth of the young female fowl the development of the oviduct and its
ligaments is in proportion to that of the body. With the elongation that
takes place about the time of functionation, as described above, the
ligaments enlarge in proportion to the enlargements of the oviduct. The
dorsal ligament maintains a line of attachment to the body wall from the
caudal end of the body cavity to the fourth thoracic rib. The ventral
ligament elongates only slightly during this developing period. It
becomes thicker and stronger and early develops a muscular coat. It also
grows in width except at the caudal end. At this point the ligament is
simply a mass of muscular tissue of the smooth or involuntary type.
These ligaments are fan-shaped.

The muscle fibers of the dorsal ligament of the laying hen, have their
origin in a line near the medial side of the dorsal margin. At this
point the bundles of fibers are quite thick, but are spread out thinly
toward the margin of the oviduct. Frequent anastomoses are noted. The
muscular fibers become continuous with the circular ones of the oviduct.

The _ventral ligament_ of the oviduct of the laying hen is largely a
muscular cord 3 to 6 centimeters in diameter. The caudal end is thicker,
becoming gradually thinner toward the anterior portion. The bundles of
muscular fibers extend toward the oviduct blending with the circular
fibers of that viscus. The ligaments terminate anteriorly in such a
manner that they aid in forming the serous ovarian pocket, which guides
the yolk into the fimbriated portion, or funnel, of the oviduct. The
walls of the ovarian pocket are formed by the left abdominal air-sac, a
part of the intestine, and the mesentery. The dorsal portion is formed
by the roof of the abdominal cavity, and the ventral portion is formed
by the dorsal wall of the air-sac. The medial, the anterior, and the
lateral limit of the pocket are formed by a fusion of the wall of the
air-sac to the mesentery and to the body wall. Posteriorly, the wall
consists of the transverse part of the small intestine and the caudal
portion of the left cæcum with their attached mesentery.




                          THE DUCTLESS GLANDS


These glands do not possess excretory ducts. They furnish materials
which are added to the blood or lymph as it passes through them. The
material from each gland is known as an internal secretion, or hormone.
Some of these secretions are powerful materials and influence profoundly
the body nutrition. The ductless glands are usually given as follows:
the spleen, the lymph glands, the pineal gland, the pituitary body, the
thyroid gland, the thymus gland, the adrenal glands, and the
parathyroids. The spleen, the pituitary, the pineal, and the lymph
glands are described in other sections.

=The Thyroid Gland= (Fig. 21, No. 16). _Location._—The thyroid gland
lies on the ventral side of the carotis communis at a point where the
carotis communis touches the jugular vein, which is about the point of
origin of the vertebral artery.

_Shape._—The thyroid gland is small, oval or somewhat roundish, and red
or rose-colored.

_Structure._—The thyroid gland has a fibrous capsule, which sends into
the interior septa which divide it into acini. These acini are closed
and contain a fluid. The thyroid is a ductless gland. Short arteries
from the carotis enter this gland, and some large veins connect it with
the jugular vein. The lymph vessels which lie along the neck are closely
connected with it and receive twigs from the gland. The minute lymphatic
capillary endings are found in its septa and in its capsule. The acini
are lined with a single or a double row of cuboidal secreting cells.
There are two kinds of cells, namely, secreting and resting cells. The
actively secreting cells secrete colloid.

The =parathyroids= consist of two small bodies attached to the lower
pole of the thyroid.

=The Thymus Gland= (Fig. 47, No. 10).—The thymus gland is an organ of
fetal and early baby chickhood. It soon undergoes retrogressive changes
into fat and connective tissue. It is of epithelial origin, being formed
in fetal life from the entodermal cells of the dorsal end of the throat
fissure.

_Location._—The thymus gland lies anterior to the thyroid, the latter
lying the deeper.

_Shape._—The thyroid consists of two lobes, which are united by
connective tissue, and appears as a loop-like acinous gland lying along
the neck and near the region of the bronchi and the jugular veins with
fibrous extensions toward the head.

_Structure._—The gland lobes are divided into lobules, which consist of
a cortical and a medullary portion. The cortex consists of nodules of
compact lymphatic tissue similar to those found in the lymph glands.
These occupy the chambers formed by the septa of connective tissue. In
the medulla there are a number of spherical, or oval bodies composed of
concentrically arranged epithelial cells. These are known as Hassall’s
corpuscles, and represent only the remains of the original glandular
epithelium. They are characteristic of the thymus gland. The thymus
appears to be a type of lymph organ. Lymph vessels are rare; a few
blood-vessels on the upper side form capillary nets.

=The Adrenal Gland= (Fig. 54, _F_). _Location._—The adrenal gland, often
called the suprarenal capsule, lies just anterior to the front part of
the anterior lobe of the kidney, adjacent to the testicles in the male
and to the ovary in the female. It is loosely attached by connective
tissue to the posterior aorta and to the vena cava.

_Shape._—It is yellowish-brown or reddish-pink in color, small, and of
irregular formation.

_Structure._—The adrenal gland consists of a cortical and a medullary
portion, although these two parts are not distinctly marked. The
cortical portion has columns which extend deeply into the gland, and the
medullary portion sends columns into the cortical portion. Therefore,
the two substances, lying side by side, form a cord-like structure.

It is probable that the cortical portion is derived from the ingrowths
of the peritoneum, and the medullary cords from the sympathetic
ganglion.

The cells are cylindrical or polygonal in shape, with an eccentric
substance between the columns. The cords, or columns, form between them,
elongated channels which extend into the interior of the gland and end
as blind or cæcal extremities. Large ganglionic nerve cells belonging to
the sympathetic system occur near the surface of the gland. The
blood-vessels are not well developed in the interior of the gland but
are numerous and of good size in the outer parts. Lymph vessels are also
present.

_Function._—The adrenals are ductless glands. They secrete an internal
secretion, or hormone, which influences the tonus of the blood-vessels.
An extract from these glands is called adrenalin.




            THE RESPIRATORY APPARATUS (Figs. 50 and 61, _A_)


Owen says: “Notwithstanding the extent and activities of the respiratory
function in birds, the organs subservient thereto manifest more of a
reptilian than of the mammalian type of formation.”

By the action of the respiratory organs certain chemical and physical
changes take place in the blood. The chief of these consists in
absorption of oxygen from, and giving off carbon dioxide to, the
atmospheric air, the former changes being necessary for the elaboration
of the fluid, the latter for the elimination of a substance which, if
retained, would prove injurious. The organs of respiration are
invariably adapted to the wants of the animal and the medium in which it
lives.

In the bird, which breathes through its nose, the organs of respiration
are nostrils, nasal chambers, pharynx, superior larynx, trachea,
inferior larynx, bronchi, bronchial tubes, lungs, and air-sacs.

=The Nostrils and the Nasal Chambers.=—The nostrils of the bird open
externally by two small elliptical openings, which pierce the upper
mandible. Within each nasal chamber (Fig. 26, _A_) are three turbinated
laminæ, or _turbinated bones_. The inferior one is a simple fold
adhering to the lower and anterior part of the nasal septum. The middle
turbinated bone is the largest. It is of infundibular form, and adheres
by its base to the septum and externally to the side wall of the nose.
It is convoluted with two and a half turns. The superior bone, of bell
shape, adheres superiorly to the frontal bone. The internal turbinated
bone extends toward the orbit; the external terminates in a cul-de-sac
behind the middle turbinal (Fig. 26, No. _A_, 1 and 2, and _G_).

The nostrils are separated by a partition which is partly bony and
partly cartilaginous. The posterior nares is represented by a long slit
in the hard palate.

=The Pharynx and the Superior Larynx.=—A transverse row of horny,
filiform papillæ marks the anterior border of the pharynx, where in
other animals the soft palate, or velum, is located. (For further
description of the pharynx see special chapter.)

The supero-posterior border of the larynx, at the juncture of the larynx
and the esophageal margin, is marked by a second transverse row of
horny, filiform papillæ, which point backward. There is no epiglottis.
The superior part of the larynx is pierced by an oval, slit-like
opening, the _glottis_, which is provided with two lips. These when
brought together, tightly close the glottis so that nothing can fall
through into the larynx in the act of deglutition. The margin, or rim,
of this opening is called the _rami glottis_. The glottis is controlled
by two pair of muscles.

The superior surface of the larynx is somewhat triangular with the apex
directed forward. A few delicate, filiform papillæ are upon its surface.
The bird has, as already indicated, two larynxes, the _superior larynx_
located at the upper end of the trachea, and the _inferior larynx_ at
the bifurcation of the trachea. The inner surface of the superior larynx
is smooth and does not contain vocal cords; it is in these animals
simply a passage for air. It is joined to the trachea inferiorly by a
ligament, the _crico-trachealis_, and lies at the base of the tongue
supported by two cornua of the os hyoideum.

The cartilages forming the principal support of the superior larynx,
consist of four pieces, as follows: one unequal ventral piece, two side
pieces, and one unequal dorsal piece. The cartilaginous, flat, ventral
_cricoid_, early in the bird’s life, often becomes bony. The side pieces
are separated from it, only exceptionally fusing with it. The dorsal
cricoid piece also often becomes bony. The two _arytenoid cartilages_,
joined with the cricoid superiorly, are three-sided, and are united to
each other in a sharp angle. They form the superior opening of the
superior larynx.

=The Trachea.=—The trachea is cylindrical and varies in length in
different kinds of birds in accordance with the length of the neck. It
consists of from 90 to 120 cartilaginous rings, complete with the
exception of the two uppermost, which rings are held together by
intercartilaginous ligaments. The tracheal rings are constructed of
hyaline cartilage and the ligaments of fibrous tissue. It is lined with
a mucous membrane covered by columnar epithelium. The trachea is a
passage for air alone and terminates in the inferior larynx.

=The Inferior Larynx.=—The inferior larynx, called the _true larynx_
because it is the organ of voice, is located at the inferior end of the
trachea and the superior ends of the bronchi. By some anatomists this
organ has been called the _larynx broncho-trachealis_. The larynx is
flattened laterally in fowls. It contains two membranous folds, which in
the production of sound are caused to vibrate. These folds are half-moon
shaped elastic structures, located in the bony, arrowlike way,
intero-inferiorly. These structures are called the _membrana tympana
interna_. In the duck this inferior larynx is represented by a drum-like
cartilaginous and bony structure, called the _bulla tympaniformis_. This
bulla is a resonant apparatus which serves to strengthen the voice.

In song birds there is a double glottis, usually produced by a bony bar,
called the _pessulus_, or _os transversale_, which traverses the lower
end of the trachea from front to rear. It supports a thin membrane which
ascends into the tracheal area, and, terminating there by a free concave
margin, is called the _membrana semi-lunaris_. This is most developed in
singing birds, and being vibratile, forms an important part of their
trilling vocal apparatus. The air passes on each side of the membrana
semi-lunaris and its sustaining bone to and from the bronchi and lungs.

The last ring of the trachea usually expands as it descends, with its
fore and posterior parts produced, and the lower lateral borders
concave; the extremities of the pessulus, butts against the angle thus
formed and expands to be attached, also with the fore and posterior
terminations of the first half ring of the bronchus, strengthening and
clamping together the upper part of the vocal framework. The second
bronchial half ring is flattened and curved with the convexity outward,
like the first, but is more movable. The third half ring is less curved
and further separated from the second, to the extremities of which its
own are connected by a ligament, and, for the intervening extent, by a
membrane; its inner surface supports the fibrous cord, or fold, which
forms the outer lip of the glottis of that side; it is capable of rotary
movements on its axis, and is an important agent in the modulation of
the voice. All these parts just described are bony.

=The Bronchi and the Lungs.=—The bronchi, two in number, are provided
with only incomplete cartilaginous rings. They enter the inferior face
of the lungs, toward their anterior and middle thirds and break up into
primary bronchi, which give off at right angles, secondary bronchi, and
these latter in turn give off tertiary branches.

[Illustration:

  FIG. 61.—The lung.

  _A._ The outer surface of one lung. Note the flattened oval shape. It
    is not divided into lobes. 1, The bronchus. 2, Primary tubules
    showing openings leading from the primary tubules to the secondary
    tubules. 3, Openings of two of the large tubes into the
    diaphragmatic and abdominal air-sacs.

  _B._ Sectioned surface of lung. 1, Secondary tubules. 2, Tertiary
    tubules. 3, Interlacing capillaries and air cells.

  _C._ 1, Cavity of tubule. 2, Its lining membrane supporting
    blood-vessels with large areolæ. 3, Perforations in the membrane at
    the orifices of the lobular passage. 4, Interlobular space
    containing the terminal branches of the pulmonary vessels supplying
    the capillary plexus, 5, to the meshes of which air gets access by
    the lobular passage.
]

The lungs occupy only about one-seventh of the thoracic space. They are
long, flattened, and oval, extending along each side of the spine from
the second dorsal vertebra to the anterior end of the kidneys, and
laterally to the juncture of the vertebral with the sternal portions of
the ribs. They present two faces, a _superior convex_ and an _inferior
concave_; two borders, an _external_ and an _internal_; and two
extremities, an _anterior_ and a _posterior_ (Fig. 61). The convex
surface is also called the dorsal, costal, or superior face. It is
moulded on the walls of the thorax and occupies a part of the
intercostal space, pushing the intercostal muscles outward. When the
surface of the lung is examined it is seen to be furrowed where the ribs
pressed during life. These furrows are as deep as the ribs are thick.
The sides of the lungs are covered with connective tissue which attaches
them to the costal walls.

The concave, or inferior, face also called the _diaphragmatic_ or
_visceral face_ is directed downward. The diaphragm separates it from
the abdominal viscera. The surface is covered by connective tissue which
closely attaches it to the diaphragm. It is perforated by the five
tubules which bring the posterior air-sac into communication with the
lungs.

The borders of the lungs extend parallel to the long axis of the body.
The internal border is rectilinear, thick, and rounded. The external
border is convex, thin, and sharp.

The anterior extremity terminates in a sharp point which occupies a
space formed by the ribs externally and the inferior spines internally.
The posterior extremity is somewhat rounded and extends as far back as
the anterior border of the kidneys.

As soon as the bronchi enter the lungs they become broadened, the
cartilaginous rings disappear, and they continue as membranous channels
whose diameters gradually decrease, as they extend backward, to the
point where they terminate in the _ostium caudale_, at which point they
are surrounded by a cartilaginous ring. The ostium caudale brings the
tubules into communication with the ventral air-sacs.

Twelve _air tubules_ have their origin from each common bronchus, or
trunk. Four are given off from the internal wall of the main bronchus by
a series of openings arranged in a row. Seven are given off from the
external wall by a second series similar to that of the first. The
twelfth extends from the inferior wall, and immediately takes a course
downward and outward and communicates with the posterior diaphragmatic
air-sac. This may be considered as the terminal branch of the trunk.

All of these secondary canals, except the last, pass toward the
periphery of the lung. They divide and subdivide at the periphery,
covering it with their ramifications. The canals extending from the
inner wall are distributed to the inferior face of the lung. Those
extending from the outer wall are distributed to the outer face of the
lung. The first constitute the _diaphragmatic_ and the second the
_costal bronchial tubes_.

The four _diaphragmatic bronchial tubes_ are numbered in the order in
which they are given off. The first is carried forward horizontally, the
second transversely inward, the third obliquely inward and backward, and
the fourth directly backward. They have, by some anatomists, been called
the anterior, the internal, and the posterior diaphragmatic bronchial
tubes. There are two posterior diaphragmatic bronchial tubes; the larger
called the great posterior, and the smaller, which passes directly
backward, the small posterior.

The _costal bronchial tubes_, seven in number, are numbered from the
front backward in the order they are given off. Parallel at their
origin, and side by side, like pipes of an organ, they soon spread out
in fan-shape like the preceding. They extend from their central origin
to the periphery. The first extends obliquely upward and inward to the
anterior extremity of the lung. All branches from this bronchus extend
from its anterior wall. The first branches are inflected to reach the
external border of the lung. The succeeding branches are directed
forward and the last forward and inward. They all meet those from the
anterior diaphragmatic bronchus, but do not anastomose with them.

The second, the third, and the fourth costal bronchi extend in a
transverse manner and ramify on the inner border of the lung.

The fifth and the sixth are directed toward the posterior extremity of
the lung. The seventh, very small, reaches this extremity, where it
disappears.

The first costal bronchus is the largest; those following it gradually
become smaller. At their points of origin they adhere closely to the
ribs. They are all imperforate, which is a distinguishing feature from
those occupying the opposite face.

The _canaliculi_ or _tertiary tubules_ given off by these secondary
bronchial tubes do not differ greatly in caliber in the various parts.
They are given off at right angles from the pulmonary wall of each
bronchus, and extend perpendicularly into the lung substance. Thus we
find three kinds of conduits, the primary, the secondary, and the
peripheral, or tertiary. The first are like the barbs of a feather on
its shaft; and the second and parenchymatous are implanted on the
pulmonary walls of the first, like the hairs of a brush on their common
base. Thus instead of the branching of the bronchi being dichrotomous,
as in mammals, it is piniform.

The canaliculi, or finer tubules, communicate with one another. The
inner microscopic appearance of the canaliculi indicate that they are
divided into areola, which gives them a cellular aspect. These tertiary
bronchi open on a dense labyrinth of blood capillaries (Fig. 61, _C_).
At this point the ciliated epithelial cells give way to simple squamous
epithelium.

Thus we find three kinds of bronchi, or their ramifications, as follows:
the primary, the secondary, and the tertiary.

=The Air-sacs= (Fig. 61, _A_).—The air-sacs are bladder-like structures
consisting of a delicate cellulo-serous membrane, an extension from the
bronchial tubes, in some places strengthened by an external envelope of
elastic fibrous tissue. Long thin blood-vessels are distributed in the
substance of these walls. They are branches from vessels of the general
circulation and not extensions from those of the lungs. No lymphatics
have been found in the air-sacs.

[Illustration:

  FIG. 61, _A_.—Diagram of air-sacs and their location. 1, The proximal
    end of the humerus. 2, The proximal end of the right clavicle. 3,
    The cervical air cell. 4, The right coracoid bone. 5, The anterior
    thoracic air cell. 6, The right side of the sternum. 7, The right
    side of the liver. 8, The peritoneum. 9, The right abdominal air
    cell. 10, The coccyx. 11, The proximal end of the right femur. 12,
    The right supero-posterior air-sac. 13, The right infero-posterior
    air-sac. 14, The right lung. 15, The axillary extension of the
    air-sac. 16, The obturator foramen. 17. The pelvis.
]

These sacs do not communicate with each other and normally they are not
fully inflated. In some locations they extend into the bones and are in
communication with the extensions of the bronchial tubes. In fact, by
some anatomists they have been called “bladder-like, extra-pulmonary
expansions of the bronchial tubes, free from cartilage.” The air-sacs
make the bird’s body lighter, thus making long-continued flight
possible. They are best developed in those birds which fly most. There
are four pairs of cells and one single cell from which all other
expansions and extensions are made. These sacs are as follows: a single
anterior thoracic, and, in pairs, cervical, anterior diaphragmatic,
posterior diaphragmatic, and abdominal.

_The Anterior Thoracic Air-sac._—The anterior thoracic air-sac is
located above the clavicles and the interclavicular space, in the cavity
of the thorax. It is related superiorly with the trachea and the
esophagus; laterally with the lungs and the cervical air-sacs;
inferiorly with the sternum, the clavicle, and the interclavicular
aponeurosis; posteriorly with the heart and the anterior diaphragmatic
reservoir; and anteriorly with the integuments of the neck. It contains
the inferior larynx and the two primary bronchi, and large vascular
trunks from which are given off vessels supplying the neck and the
wings.

Three prolongations, called subpectoral, subscapular, and middle, or
humeral, arise from the lateral walls of this air-sac. These
prolongations cross the walls of the thorax and pass around the
articulation of the shoulder.

The _subpectoral prolongation_ extends from the thoracic reservoir by an
orifice situated behind the coracoid, and passes beneath the tendon of
the great pectoral muscle. When the pectoralis major contracts, this
contraction dilates the subjacent cell and draws into it a greater
quantity of air.

The _subscapular_ and the _humeral prolongations_ communicate with the
thoracic air cell by a common opening situated behind the small adductor
muscle of the humerus. The subscapular prolongation, after leaving this
point, spreads under the scapular and the subscapular muscle, which it
separates from the ribs and corresponding intercostal muscles, and
extends in a longitudinal direction.

The humeral prolongation, smaller than the subscapular, occupies the
axilla, and is in shape triangular. It has from its summit into an
infundibular fossa, an extension which enters the canal of the humerus.
The walls of this cell form the lining of the air space in the humerus.

The thoracic air-sac thus possesses numerous membranous folds which
divide its cavity. The contiguous structures which it overlies, as the
trachea, the esophagus, the muscles of the inferior larynx, as well as
the arteries and veins, make its outer walls irregular. This orifice is
dilated during inspiration, by the contraction of the two first
fasciculi of the diaphragm.

_The Cervical Air-sacs._—The two cervical air-sacs are located just
above the thoracic air-sac at the inferior part of the neck and in front
of the lungs. They are cone-shaped with the base directed forward and
the apex backward. They are related superiorly with the cervical
muscles, and inferiorly with the thoracic air-sac from which they are
separated by the trachea, the esophagus, the pneumogastric nerve, and
the jugular veins. The walls touch each other internally, and form a
median septum which includes in its substance the two common carotid
arteries. Externally they are related to the origin of the cervical
nerves, to each of which they contribute a small sheath. They surround
the vertebral artery, and are connected with the subcutaneous muscles
and the skin. The summits communicate with the anterior diaphragmatic
bronchus. Prolongations extend from their bases which conduct the air
into all the vertebræ of the neck and the back, into all the vertebral
ribs, and into the spinal canal. Parallel with and adjacent to the
vertebral arteries, and lodged in the canals excavated in the transverse
processes of the cervical vertebræ, are two cervical prolongations, one
on each side, which extend to the cranium from the base of the cervical
reservoirs. From their sides, at the last six cervical vertebræ, are six
extensions in the form of diverticuli, which, lying against each other,
pass from each side into the muscles of the neck. They are surrounded by
a thin fibrous envelope, a continuation of the mucous lining of the sac,
and apparently form a canal in the inferior part of this region. These
prolongations are better developed in palmipedes than in chickens. On
the internal side of these prolongations, one or more foramina penetrate
the vertebral segment, which allow the extensions of the prolongations
into the spinal canal. Chauveau states that “as the medullary tissue is
replaced by air in the bones of birds, so is the subarachnoid fluid
replaced by air around the spinal cord.”

The prolongations extending from the cervical air-sacs, having entered
the thorax, terminate by passing into the first dorsal vertebra. After
permeating every part of this vertebra, it escapes by a lateral opening
and forms a small sac located between the first two ribs, near the
origin of the first dorsal nerve. From this sac an extension is given
off, which enters the second vertebral segment at the antero-lateral
part; from this point it passes back, forming a new air-sac between the
second and third ribs. It now passes in the same manner into the third
vertebra and extends through the third intercostal sac, and so on till
the last dorsal vertebra has been served. At the same time that these
sacs receive the air from the vertebræ preceding them, and transmit it
to those which follow, they communicate it to all the vertebral ribs.
The aerial currents which leave the cervical air-sacs do not communicate
with those of the cranium. Experiments show that the cranial bones have
apparently no communication with the respiratory apparatus.

_The Anterior Diaphragmatic Air-sac._—The two anterior diaphragmatic or
supero-posterior air-sacs are related with the lungs anteriorly, and
with the abdominal viscera posteriorly. Anteriorly also is the thoracic
air-sac, posteriorly are the posterior diaphragmatic air-sacs, and
laterally the ribs and the intercostal muscles and internally is the
esophagus. The lungs communicate with these air-sacs through circular
openings from the great posterior diaphragmatic bronchus and frequently
by a second opening from this same tube. These are the only sacs which
receive air from the lungs through two openings.

_The Posterior Diaphragmatic Air-sac._—The two posterior diaphragmatic,
or infero-posterior air-sacs are oval in shape and located between the
thoracic and the abdominal cavity. They are related anteriorly with the
anterior diaphragmatic air-sacs. These two sacs form a vertical
transverse partition. The posterior diaphragmatic air-sacs are related
posteriorly with the abdominal air-sacs from which they are separated by
the diaphragm. They are related below with the lateral parts of the
sternum and the sternal ribs, and externally with the ribs and the
intercostal muscles. These air-sacs communicate with the lungs through
openings located in the middle part of the external border of the lung,
into the extremity of voluminous bronchial tubes which follow the
direction of the largest air tubes.

_The Abdominal Air-sacs._—The two abdominal air-sacs located on each
side of the abdominal cavity, when inflated with air, form enormous
bladder-like structures. They are related laterally with the abdominal
wall and internally with the abdominal viscera. The anterior extremities
are in communication with the mesobronchi and are somewhat inflected to
pass under the fibrous arches extending from the spine to the pelvis.
Anteriorly these sacs adjoin the diaphragm, the testes in the male, and
ovary in the female, and to the parietes of the abdomen and those of the
pelvis. Below and in front, they rest on a fibrous septum, which in all
birds divides the abdominal cavity into two smaller cavities: one
anterior, representing the abdomen and containing the liver; the other
posterior, representing the pelvis and containing the gizzard and the
intestines. The anterior portion overlies the posterior part of the
lobes of the liver, the proventriculus, the spleen, and the gizzard. The
kidneys are located above these air-sacs. Dorsal to the sacs is also a
part of the intestines and in the female the oviduct. The abdominal
air-sacs are attached by a ligament-like structure in their medial,
their anterior, and their lateral margin. The posterior, the dorsal, and
the ventral margin are free. Mesially this attachment is to the
mesentery, connecting the left cæcum to the dorsal margin of the
gizzard, and also to the mesentery of the proventriculus. The anterior
attachment is to the body wall and extends in front of the end of the
ovary and the adrenal glands. At the antero-lateral part of the body
cavity the attachment extends in a widening band along the lateral side
of the ovary and of the oviduct, as far back as the caudal margin of the
sac. The lateral attachment is related to the kidney, the dorsal
ligament of the oviduct, and the abdominal wall.

Each of these abdominal sacs has three extensions: one suprarenal and
two femoral.

The _suprarenal extension_ leaves the principal sac at the
postero-external part of the kidney, extends upward, and forward, and
expands over the surface of the kidney. At the internal border of the
kidney, this prolongation extends between the transverse processes of
the sacral vertebræ, reaches a height of the first dorsal vertebra,
forms a triangular canal located above the sacrum in the sacral channel,
and is separated from its fellow by a series of corresponding spinous
processes.

The two _femoral extensions_, an anterior, small, and a posterior,
large, extend from the abdominal air-sac at the cotyloid cavity, leave
the pelvis through the bony passage occupied by the crural vessels,
extend around the coxo-femoral articulation, and terminate in a blind
extremity. In some birds, particularly in birds of prey and ostriches,
there are prolongations extending into the femur, entering through a
foramen at the anterior part of the great trochanter.

_Summary of Bones Supplied by Each Air-sac._—The thoracic air-sac
communicates on each side of the thorax with twelve bones, including the
four sternal ribs. It supplies air to the clavicles, which are
perforated at both their extremities, and to the coracoids, which are
perforated just below their scapular extremity. The sternum is supplied
through two series of openings, the middle ones that conduct air into
the sternal ridge and the lateral ones, eight in number and very small,
correspond to the intercostal spaces. The sternal ribs are penetrated by
small foramina at their inferior extremities. From the subscapular
extension the scapulæ receive air through one or two foramina at their
anterior extremity. The humeral prolongation supplies the humerus
through a foramen located at the upper edge of the humeral fossa, at the
infero-internal part of the articular head.

The cervical air-sac furnishes air to all the cervical vertebræ, to all
the dorsal vertebræ, and to all the vertebral ribs. The anterior parts
of the vertebræ of the neck are supplied with air through the passage
accommodating the vertebral artery. The posterior parts of the vertebræ
are supplied by extensions from the interspinal canal. The first
extensions obtain entrance to the anterior segments by one or more
openings of the inner wall of the intertransverse canals; the median
extensions penetrate the posterior segments by two openings, a right and
a left, situated on the inner wall of those segments. The first dorsal
vertebra is supplied with air in the same manner, by the middle and the
lateral canals of the neck. This air, after passing through the first
vertebra, leaves by a lateral exit to enter a small air-sac. From this
it passes into the superior part of the second vertebra, escapes from
this through its lower portion, to be received into a lateral sac, and
so on to the last dorsal vertebra. These sacs also supply the vertebral
ribs with air, which enters them by very small openings located on their
spinal extremities.

The diaphragmatic air-sacs do not have communications with the bones.

The abdominal air-sacs communicate with the sacrum, the coccygeal
vertebræ, the iliac bones, and the femurs. The air passing through the
sacrum, the coccyx, and the ilium comes directly from the suprarenal
extensions; the air which fills the femoral cavity comes from the
femoral extensions.

In some birds these air spaces are more greatly developed than in
others. The bones that are always aerated in all birds are the cervical
and the dorsal vertebræ, the sternum, and the humeri. Those aerated in
some kinds only are the furculum, the scapulæ, the vertebral and the
sternal ribs, the sacrum, the coccyx, and the femurs. Those that are
never aerated are the bones of the forearm, the hand, the leg, and the
foot.

The service of air to the bones in most parts of the body by the
air-sacs, as just shown, is in special cases otherwise rendered. The
Eustachian tubes furnish air to the bones of the cranium and to the
upper jaw; while the lower jaw receives air from the pneumatic foramen
situated upon each ramus behind the tympanic articulation, and from an
air cell which surrounds the joint.

The cavities of the embryonic bones, which afterward become pneumatic,
are filled with marrow. Selenka states that the invasion of the bones by
the air is a late development, and that in the humerus this invasion
occurs after the twenty-second day in the life of the chick.

Hunter and Compar, who have made extensive researches, consider the
function of the air-sacs as threefold.

First, the air-sacs are subsidiary respiratory organs, which aid in
ridding the blood of waste products and in taking in oxygen.

Second, they aid mechanically the actions of respiration in birds.
During the act of inspiration the sternum is depressed, the angle
between the vertebral and the sternal ribs is made less acute, and the
thoracic cavity proportionately enlarged; the air then rushes into the
lungs and into the thoracic receptacles, while those of the abdomen
become flaccid. When the sternum is raised, or approximated toward the
spine, part of the air is expelled from the lungs and the thoracic
air-sac through the trachea, and part is driven into the abdominal
receptacles, which are thus alternately enlarged and diminished with the
expansion and the contraction of the thorax. Hence the lungs,
notwithstanding their fixed condition, are subject to due compression
through the medium of the contiguous air receptacles, and are affected
equally and regularly by every motion of the sternum and of the ribs.

Third, they reduce decidedly the specific gravity of the whole body.
This must necessarily follow from the large spaces filled with air as
well as from the absence in the bones of marrow and other fluids. The
air-sacs by their position also render equilibrium more stable.




                               ANGIOLOGY


=The Circulatory Apparatus.=—The circulatory apparatus consists of two
tubular systems: the blood vascular system and the lymphatic system.

The blood vascular system consists of the heart, the arteries, the
veins, and the capillaries.

The heart is the central, propelling organ. The arteries form a series
of efferent tubules, which, by branching, constantly increase in number
and decrease in caliber, and which serve to carry the blood from the
heart to the tissues. The capillaries are extensions from these latter
tubules into which the arteries empty, and through the walls of which
the interchange of elements between the blood and the other tissues
takes place. The veins form a system of converging tubules which receive
the blood from the capillaries, decrease in number and increase in size
as they approach the heart, and return the blood to that organ.

The lymphatic system consists of capillaries and veins alone. As in the
blood system, the lymph capillaries collect the effete material and pour
it into the lymph veins, and these in turn, carry it to the large blood
veins adjacent to the heart.

Both these systems have one and the same continuous lining, which
consists of a single layer of endothelial cells. In the heart this
lining is called the endocardium, and in the vessels, the endothelium.
It forms a perfectly smooth surface.


                       THE HEART (Fig. 21, No. 7)

The heart of the domestic fowl is located in the median line of the
thoracic cavity. It is more anterior and mesial than in mammals. Its
axis is parallel with the axis of the trunk. The lungs being confined to
the dorsal part of the trunk, the lower part of the heart is not
surrounded by them, but extends backward, the apex resting in the
anterior part of the anterior median fissure of the liver.

The heart has the form of an acute cone (Fig. 50, No. 1), the apex of
which is bluntly rounded.

The heart is surrounded by a sero-fibrous sac, the _pericardium_. This
sac adheres to the cervical air reservoirs anteriorly and to the
diaphragmatic septum posteriorly. It is composed of two membranous
layers: the _parietal_, external, dense, and fibrous; and the
_visceral_, internal, and serous. The pericardial sac has no direct
attachment to the heart, except at the upper extremity where it
surrounds the large vessels emerging from it. The serous layer is
reflected over the outer portion of the heart, where it is called the
epicardium. The function of the pericardium is to prevent friction
during the beating of the heart. It contains a small amount of serous
fluid for perfect lubrication. This fluid is called the liquor
pericardii.

Internally the heart has four cavities: two auricles and two ventricles.
The _right ventricle_ is more crescent-shaped than in solipedes, and in
a manner envelops the left ventricle in front and to the right, though
it does not reach the point of the heart. The _right auricle_ is larger
than the left. The _auriculo-ventricular_ valve is not tricuspid as in
mammals. This valve instead of being formed as usual by a membranous
curtain, with margins retained by cords fixed to the walls of the
ventricles, is composed of a wide muscular leaf, which appears to be a
portion of the inner wall of the ventricle detached from the
_interventricular septum_. This septum is convex; and the
auriculo-ventricular orifice is an oblique slit situated between it and
the muscular valve in question; so that, when the heart wall contracts
at the systole, the valve is applied against this septum and closes the
passage. The bicuspid, or auriculo-ventricular valve of the left side
usually has two segments, though occasionally there may be three. The
_fossa ovalis_ is a depression behind the posterior semi-lunar valve in
the septum of the heart. The membranous septum closing the foramen ovale
is complete and strong but thin and transparent. The right auricle
receives the blood from the two venæ cavæ coming from the anterior
extremity, and from the posterior vena cava. These empty into a sinus.
The left auricle has two vessels, the pulmonary veins which bring blood
to it from the lungs.


=Structure of the Heart.=—The heart is lined by a serous membrane, the
_endocardium_, which is a continuation of the endothelium of the
blood-vessels. There are a few muscular pillars in the inner wall,
called the _columnæ carnæ_. To give the heart its pumping power, it is
made up of contractile tissue, a specialized kind of muscle called
_heart muscle_. It is involuntary-striated and occupies an intermediate
position, both morphologically and embryologically, between smooth
involuntary muscle and striated voluntary muscle (Fig. 74, No. 4). It,
like striated voluntary muscle, is both transversely and longitudinally
striated. Heart muscle cells are short, thick cylinders, which are
joined end to end to form long fibers. By means of lateral branches the
cells of one fiber anastomoses with cells of adjacent fibers. Each cell
of heart muscle contains one centrally located nucleus. There is no
distinct sarcolemma, but the sarcoplasm is more dense near the surface
of the cell, which gives it the appearance of an enveloping cell wall.
There is a zone free from fibrillæ around the nucleus. The longitudinal
fibrillæ, which make up the cell, are held together by a cement-like
substance.

The main mass of the heart wall, called _myocardium_, consists of the
specialized muscular tissue just described. The myocardium differs in
thickness in different parts of the heart wall. It is thickest in the
left ventricle and thinnest in the auricles. The left ventricle forces
the blood through the systemic circulation and hence must be thicker to
give it more power than is needed for the right ventricle, which forces
the blood only through the lungs. The auricles are thinnest of all; for
they receive the blood and pass it only to the chambers below. The
_auricular appendages_ at the base of the heart in fowls are not so well
marked as in mammals. The auricular muscles consist of an outer coat
common to both auricles, the fibers of which are transverse and of an
inner coat, independent for each auricle, the fibers of which are
longitudinal. Between the two coats, occur bundles of muscle the fibers
of which run in various directions. The disposition of the muscle tissue
of the ventricles is much more complicated. It is composed of several
layers of fibers intricately interwoven.

The _endocardium_, covering the inner surface of the myocardium, forms a
serous lining of all the chambers of the heart. At the arterial and
venous openings it is continuous with and similar in structure to the
intima of the vessels. The endocardium consists of two layers, an
external layer closely attached to the myocardium and consisting of
mixed fibers, including those of elastic tissue and smooth muscle cells;
and an inner, single layer of endothelial cells, spoken of above.

The heart is supplied with nutrient blood by the two _coronary
arteries_, which are given off from the common aorta just above the
semi-lunar valves.

A right, or anterior, and a left, or posterior, coronary from their
point of origin, turn in a ventral direction between the root of the
aorta and the pulmonary artery, the right going to the right coronary
groove and the left to the left coronary groove in the crown furrow.
From here they send branches into the heart. The anterior, right,
coronary, or coronaria dextra, the larger, is given off from the
inferior wall of the aorta. It divides into a ramus superficialis and a
ramus profundus. The ramus superficialis enters the crown furrow and
divides into two or three branches on the right heart wall. These
branches extend to the apex of the heart. Twigs from this artery along
its course extend into the muscular wall reaching the posterior of the
coronary groove where they anastomose with those of the left coronary,
the ramus profundus, and with other branches from the same artery. The
ramus profundus, larger than the preceding, gives off fine branches into
the walls of the aorta and of the pulmonary artery, then enters from
behind into the right wall of the septum ventriculorum, extends into the
apex of the heart, and supplies the septum, or right inner chamber wall
with the last branch, this breaking through the posterior wall of the
auricular appendage.

The posterior, _left coronary_, or _coronaria sinistra_, originates from
the dorsal wall of the aorta, proceeds as one branch on the upper
surface of the left auricular appendix, and then extends between the
left appendix and the pulmonary artery to the ventral surface of the
heart. On the left side it supplies the wall of the pulmonary artery and
gives off a ramus profundus. It sometimes divides into two parts and
supplies the ventral wall of the right chamber and then extends to the
left wall of the septum medium. The rest of the coronaria sinistra
enters into the left crown furrow as the ramus superficialis, which
provides the left and dorsal upper surface of the left chamber to the
apex. From this furrow it extends into the left chamber and the left
appendage, and finally fuses with the ramus superficialis of the
coronaria dextra.


                           THE BLOOD-VESSELS

The blood-vessels consist of arteries, veins and capillaries.

=The Structure of the Capillaries and Arteries.=—The capillaries are
minute vessels which connect the _arterioles_, or terminal arteries,
with the _venules_, or terminal veins. They are only from 6 to 14
microns in diameter. Their walls consist of a single layer of
endothelial cells, which are somewhat elongated in the long axis of the
vessels. Their edges are serrated, and are united by a small amount of
intercellular cement-like substance. Capillaries branch without
diminution in caliber, and these branches anastomose to form capillary
networks, the meshes of which differ in size and shape in different
tissues and organs. The largest meshed networks occur in the serous
membranes and in the muscles; and the smallest occur in the glands, such
as the liver.

The _walls of the arteries_ are thick and stand open when empty, owing
to the elastic tissue contained in their walls, while the walls of the
veins collapse when empty, owing to their containing a smaller amount of
elastic tissue. The arterial wall is provided with three coats: _tunica
intima_, or inner coat; _tunica media_, or median coat; and _tunica
adventitia_, or outer coat.

The _tunica intima_ consists of a single layer of endothelial cells,
continuous with and similar to that forming the walls of the
capillaries. In passing from the capillaries to the arterioles, there is
first a thin coat, or sheath-like layer, of connective tissue around the
outside of the endothelial tubes. Further along, isolated smooth muscle
cells arranged in a circular manner occur between the endothelial layer
and the layer of connective tissue, this structure forming vessels
called precapillary arteries. Further along still, the muscle cells form
a complete layer; in this section the vessels are called arterioles and
are made up of three coats: the inner endothelial, the middle muscular,
and the outer fibrous.

In arteries of medium size the intima consists of the endothelial layer,
a layer of delicate white and elastic fibers, connective-tissue cells,
and the membrana elastica interna, or an outer layer, the elastic layer,
of the intima.

The _media_ consists of a thick coat of circularly arranged smooth
muscle cells, its thickness depending largely upon the size of the
vessels. There is also a small amount of fibrillary connective tissue,
which supports the muscle cells. Elastic tissue is present in the media,
the amount depending on the size of the vessel, the larger the vessel
the more elastic tissue there is present. In the large arteries coarse
elastic fibers intermingle with the finer ones. When much elastic tissue
is present the muscle cells are separated into more or less well-defined
groups.

The _adventitia_ is composed of loose connective tissue with some
elastic fibers. A few smooth muscle cells are present, which, as are
also the elastic fibers, are arranged longitudinally. The adventitia,
blending with the connective tissue surrounding the arteries, serves to
anchor the vessels to the surrounding structure.

=Structure of the Veins.=—In many respects the walls of the veins
resemble those of the arteries. The same three coats exist and the same
elements enter into their structure. The transition from capillary to
small veins, and from those to larger veins, is similar to the
transition from the arteries to capillaries, in inverse order. The walls
are not so thick as those of arteries. The elastic tissue is much less
in quantity and in smaller veins disappears. There is not a clear line
of demarcation between the intima and the media.

The veins of birds differ from those of mammals in that they have fewer
_valves_. The valves are also less perfect, and often permit a backward
flow of blood.

The walls of the arteries and of the veins are supplied with nutrient
blood-vessels. These are called the _vasa vasorum_, or blood-vessels of
the blood-vessel wall. They are mostly in the adventitia. They may arise
from the vessel to which they are distributed or take origin from an
adjacent vessel. These small arteries supplying the vessel coat after
terminating into capillaries form small veins through which the blood,
from the structure of the vessel wall, is returned.

The walls of the blood-vessels are supplied with both medullated and
non-medullated nerves. The non-medullated nerve fibers are axones of the
sympathetic neurones and control the caliber of the vessels. These
fibers are called the _vasomotor nerves_. They form plexuses in the
adventitia, from which are given off branches which penetrate the media
and terminate on the muscle cells. The medullated nerves are the axones
of the spinal nerves. The larger fibers are found in the connective
tissue outside the adventitia and give off branches to the media where
they divide repeatedly, lose their sheath, and terminate in the media
and at times in the intima.


                          THE ARTERIAL TRUNKS

The _common aorta_ is short; it originates from the left ventricle (Fig.
61_B_, No. _K_, 14), and is guarded by three _semi-lunar valves_. The
aorta breaks through the pericardium just to the right of the pulmonary
arteries in a ventral direction; it then turns upward dorsally and to
the right of the inferior bodies of the vertebræ. It is then directed
anteriorly, and dorsally to the right bronchus, between the right
bronchus and the right lung. The right and the left coronaries are given
off from the common aorta; they have been discussed. There is next given
off the left brachio-cephalic or _brachio-cephalic sinister artery_
(Fig. 61_B_, No. _K_, 10), which is just above the border of the base of
the heart. This artery passes upward and slightly forward, over the
center of the inferior larynx. Just beyond this point the _subclavian
artery_ is given off; this artery later becomes the axillary and the
axillary the brachial artery. Then there is given off the anterior and
the posterior thoracic arteries; and finally, the pectoral, which supply
the pectoralis muscles and later terminate in the carotid, the
vertebral, and the cervical arteries. The carotid artery gives off an
esophageal artery. The other arterial trunk given off from the common
aorta is the right brachio-cephalic or brachio-cephalic dexter (Fig.
61_B_, No. _K_, 18). The right brachio-cephalic artery gives off the
subclavian, which continues as the axillary, and continues as the
brachial artery. There is given off the anterior and the posterior
thoracic, the right carotid (Fig. 61_B_, No. _K_, 11), the vertebral,
and the dorsal. The last continues as the cervical.

[Illustration:

  FIG. 61_B_.

  _K._ The arterial trunks. 1, The middle sacral artery. 2, The
    hypogastric
  artery. 3, The posterior mesenteric artery. 4, The ischiadic artery.
    5, The
  femoral artery. 6, The renal artery. 7, The left pectoral artery or
    thoracico
  caudalis. 8, The left axillary artery. 9, The left carotid artery. 10,
    The left
  brachio-cephalic artery. 11, The right carotid artery. 12, The right
    brachial
  artery. 13, The right pectoral artery. 14, The common carotid artery.
    15,
  The posterior aorta. 16, The celiac axis. 17, The anterior mesenteric
    artery.
  18, The right brachio-cephalic artery. 19, The auricular portion of
    the heart.
  20, The ventricular portion of same. 21, Sterno-clavicular artery. 22,
    Anterior
  thoracic.

  _L._ The venous trunks. 1, The caudal vein. 2, The coccygeo-mesenteric
    vein. 3, The posterior mesenteric vein. 4, The anterior mesenteric
    vein. 5, The gastro-duodenal vein. 6, The portal vein. 7, The
    hepatic vein. 8, The left anterior vena cava. 9, The left pectoral
    vein. 10, The left brachial vein. 11, The left jugular vein. 12, The
    right jugular vein. 13, The right brachial vein. 14, The right
    pectoral vein. 15, The right anterior vena cava. 16, The posterior
    vena cava. 17, The common iliac vein. 18, The femoral vein. 19, The
    renal vein. 20, The internal iliac vein. 21, The hypogastric vein.
    22, The auricular portion of the heart. 23, The ventricular portion
    of same.
]

The _pulmonary arterial trunk_ is given off from the conus arteriosus of
the right ventricle. It is guarded at its origin by three semi-lunar
valves similar to those of the aorta. The trunk divides into two
pulmonary arteries, which are short, one called the pulmonalis dexter
and the other the pulmonalis sinister. The former goes to the right and
the latter to the left lung. Each branch penetrates the lung near the
bronchus. These arteries divide, or branch, similarly to the bronchi.
Following the branchings of the bronchi, they finally terminate into the
lung capillaries, forming networks on the bronchi and the air-tube
terminals.


                BRANCHES OF THE BRACHIO-CEPHALIC ARTERY

                               ( Thyroidea
                               (              ( Cervicalis inferior
                               ( Vertebralis  ( Vertebralis anterior
                               (              ( Vertebralis posterior
                               ( ( Arteria cervicalis ascendens
                               ( Bronchiales
                  ( Truncus    ( Inferior esophageal
                  (  caroticus ( Subcutaneous colli
                  (            (              ( Carotis cerebralis
                  (            ( Carotis      ( Cervicalis superior
                  (            (  communis    ( Occipitalis
                  (            (              ( Carotis externa
                  ( ( Spinalis anterior ( Basilaris ( Cerebelli inferior
 Brachio-cephalic (
                  (                                  ( Clavicularis
                  (            ( Sterno-clavicularis ( Sternalis
                  (            (                     ( Acromialis
                  (            (
                  (            (              ( Subscapularis
                  (            (              (            ( Ulnaris
                  ( Subclavia ( Axillaris ( Brachialis ( Brachialis
                     profunda
                               (              (            ( Radialis
                               ( ( Humeralis ( Circumflex humeralis
                               (              (            (  anterior
                               (
                               (              ( Thoracica externa
                               ( Thoracalis ( ( Arteria thoracica
                                              ( Thoracica inferior (
                                                 longa
                                              (
                                              ( Mammaria interna

                               ( Circumflex humeralis posterior
           Brachialis profunda ( Collateral ulnaris
                               ( Collateral radialis

The cord-like remnant of the _ductus botalli_, or embryonal connection
between the lung arterial trunk and the anterior aorta, has been
observed but is rare in grown birds.

The arteries, the veins, and the lymphatic vessels of birds anastomose
far more frequently than those of mammals.


           BRANCHES OF THE ARTERIA CAROTIS CEREBRALIS INTERNA

                    ( Occipitalis         ( Occipitalis sublimis
                    ( ( Occipitalis profunda ( Meningea
                    (                     ( Temporalis
                    ( ( ( Rete temporale
                    ( Ophthalmica ( Recurrent ophthalmicum ( Rete
                       ethmoidalis
                    ( externa ( Ethmoidalis
                    (                         ( Plexus palpebralis
                    ( ( Plexus alveolaris inferior
                    (                         ( Plexus muscularis
 Carotis cerebralis ( Plexus temporalis       ( Plexus lacrimalis
                    (                         ( Ramus ciliaris posticus
                    (                         ( Meningea media
                    (
                    ( ( Sphenoidea ( Ethmodalis
                    ( ( Spheno-maxillaris ( Ethmoidalis ( externa
                    ( ( ( Ophthalmica ( ( Ethmoidalis
                    ( ( ( interna ( ( interna
                    ( Cerebralis   (           (
                                   ( Ramus     ( Sylviæ
                                   ( anterior ( Cerebralis profunda (
                                      Choroid plexus
                                   ( Arteria centralis retinæ
                                   ( Ramus posterior


                BRANCHES OF THE ARTERIA CAROTIS EXTERNA

                                   ( Hyoidea
                  Carotis externa  ( Laryngea superior
                                   ( Facialis
                                   ( Lingualis


                BRANCHES OF THE ARTERIA CAROTIS FACIALIS

               ( Auricularis
     Facialis  ( Facialis interna ( Alveolaris inferior ( Mentalis
               ( Maxillaris interna
               ( Facialis externa


                     BRANCHES OF THE CAROTID TRUNK

The =carotis communis= artery springs from the carotid trunk of the
brachio-cephalic. It is directed horizontally, ascending to the ventral
side of the neck. It then extends downward to the inferior median neck
region. Just after leaving its origin it gives off several small
branches to the bronchi and to the esophagus, and extends toward the
head. The carotid lies on the thyroid gland and at this point touches
the jugular vein (Fig. 21). At this point the =thyroid arteries= are
given off from the carotid trunk. The thyroid gland also receives blood
from the bronchialis artery.

Dorsalward and near the thyroid gland the carotid artery gives off a
branch (the bronchialis) which accompanies the recurrent laryngeal
nerve, along the inferior larynx and the bronchi, and supplies the lung
substance and that part of the esophagus in this region.

The =vertebral artery= is given off from the carotid trunk, dorsalward
to the thyroid gland, and on the left side. The right vertebral artery
may be given off from the brachialis dextra or right brachialis.

The =inferior esophageal artery= is given off from the ventral side of
the carotid, supplies the esophagus, extends then to the skin of the
neck and to the trachea, is directed anteriorly toward the head and
anastomoses with the vertebral artery. This artery accompanies the vagus
nerve and forms a collateral artery to the carotid and the vertebral
artery.

The =subcutaneous colli= springs from the carotid artery near the
thyroid gland and communicates with the inferior cervical artery, which,
in turn springs from the vertebral artery.


=The Common Carotid.=—Near the last cervical vertebra the two carotid
arteries occupy the same channel, to which they are attached by fascia,
and, lying close to the inferior surface of the bodies of the cervical
vertebræ, are covered by the colli muscles. Near the third or the fourth
cervical vertebra, the two carotid arteries separate. Near the atlas
each carotid divides into the _carotis cerebralis_ and _carotis
externa_. Near this division the _superior cervical artery_ branches
off. This latter artery extends down the neck in company with the
pneumogastric nerve and the jugular vein, supplies the skin and the neck
muscles, and anastomoses with the inferior cervical artery and the
subcutaneous colli artery.

The _occipital artery_ originates either from the carotis communis or
sometimes from the superior cervical.


                   BRANCHES OF THE CAROTIS CEREBRALIS

The branches of the carotis cerebralis are as follows:

1. The =occipitalis= (Fig. 72, No. 18), which in turn gives off, first,
the occipitalis sublimis. The _occipitalis sublimis_ supplies the outer
and the middle portion of the digastricus and the posterior
mylo-hyoideus muscle. It also gives off, second, the _occipitalis
profunda_ which supplies the inner portion of the digastricus muscle and
becomes the _meningeal artery_, which passes through the foramen vagi,
entering the brain cavity, where it supplies the coverings of the brain
as far as the sella turcica. Superficial branches of this artery are
distributed to the muscles in the region of the atlas and anastomose
with the vertebral artery.

2. The =ophthalmica externa=, which passes below the articulation of the
quadrate bone, around the tympanic cavity, enters the canalis caroticus,
and passes into the cranial cavity. The ramus occipitalis, passing out
of the same foramen, again enters the diploë of the cranium; then after
passing dorsally over the upper outer semicircular canal of the ear,
passes backward through the occipital bone.

The ophthalmica externa (Fig. 72, No. 9) forms a main trunk and gives
off two branches: the _temporal artery_ and the _recurrent ophthalmic_.
The recurrent ophthalmic gives off the _rete temporalis_, _rete
ethmoidalis_, a branch to the orbital gland, and finally anastomoses
with its own branches and with those of the internal ophthalmic at the
olfactory foramen and aids in forming the _ethmoidal artery_. These
arteries supply blood by giving off branches to the muscles of the eye,
sclerotic coat, iris, choroid coat, and the ciliary bodies. It gives off
another branch to Harder’s gland, and finally anastomoses with the
ethmoidalis.

3. The =plexus temporalis=, rete mirabile ophthalmicum, or wonderful
network (Fig. 72, No. 8), is formed between the second and the third
trunk of the trigeminus nerve and the rete ophthalmicum.

Inferior to this is the _alveolar plexus_, which plexus accompanies the
third branch of the trigeminus into the lower jaw. Two main branches
form this plexus, one coming from the carotis facialis, which
anastomoses with the alveolar artery.

The _palpebral plexus_ lies between the trunks of the trigeminus, and
supplies mainly the lower eyelid.

The _plexus muscularis_ extends to the fifth portion of the temporal
muscle.

The _plexus lacrimalis_ forms on the posterior orbital wall on the ramus
ethmoidalis and supplies the lacrimal gland and the upper eyelid. It
anastomoses with branches from the facial artery.

The _ramus ciliaris posticus_ supplies the inferior rectus and the
external rectus muscle of the eyeball. It anastomoses with the
ophthalmica externa.

The _median meningeal artery_ passes through the foramen occupied by the
second branch of the trigeminal nerve. Passing into the cranial cavity,
it supplies the dura mater. Before passing into this foramen, small
branches are given off, which supply the skin and the temporal muscle;
and some branches anastomose with the superior cervical and the
ethmoidal arteries.


=4. The Cerebral Artery.=—Each cerebral artery enters the cranial cavity
through the canalis caroticus located in the sphenoid bone, passes
forward medially from the cochlea, dorsally from the Eustachian tube,
and passes through a small canal which opens on the inner surface of the
sella turcica. Originating in this foramen, the _sphenoid artery_
divides into two branches which anastomose with the pterygoidean and the
pterygo-pharyngeal artery and which supply the upper jaw and the throat
regions.

The _spheno-maxillaris artery_ supplies the gums.

The right and the left cerebral arteries unite at the sella turcica.
After this union they divide again immediately and pass to the base of
the brain, where they give off twigs to the optic nerve, to the optic
chiasm, and where also is given off the arteria retinæ centralis.
Passing posteriorly each cerebral artery gives off the _ramus
posterior_, and then passes to the side of the cerebellum.

The _basilar artery_, a continuation of the anterior spinal artery, is
located ventrally and mesially to the cerebellum. Laterally and
inferiorly the basilar artery gives off the inferior cerebellar artery.

The _ramus anterior_ is given off from the cerebralis artery and
continues as the _internal ophthalmic artery_. The ramus anterior also
gives off the _sylvian artery_, which supplies the sides of the cerebrum
and the middle brain. In the fissure between the hemispheres and the
optic thalamus is located the _arteria cerebri profunda_. This artery
passes along the median surface of the cerebrum and in its course
supplies the adjacent parts. It enters into the formation of the choroid
plexus of the lateral ventricle.

The _internal ophthalmic artery_ extends out of the cranial cavity,
through the optic foramen, into the orbital cavity. It passes upward
along the interorbital wall and supplies the optic nerve, the trigeminus
nerve trunk, and the eye muscles, and dorsally anastomoses near the
olfactory nerve with the rete ethmoidale and the external ophthalmic
artery, and continues as the ethmoidal artery.

The _ethmoidal artery_ supplies the supra-orbital gland and the gland of
Harder. It gives off twigs to the rete ophthalmicum and other branches
to the skin of the frontal region, where it anastomoses with branches of
the external facial artery. These branches in the frontal region are
rather large. Large branches are given off to the comb.

The _arteria ethmoidalis externa_ originates in the nasal cavity from a
division of the ethmoidal artery.

The external ethmoidal artery passes below the lacrimal bone, extends
forward, supplies the walls of the nasal cavity, and finally sends a
branch anteriorly into the upper median portion of the jaw bone, and
other branches to the septum nasi and other parts of the nasal cavity.

There are frequent anastomoses between the ethmoidalis interna, the
facialis, and the spheno-maxillary artery.

The _internal ethmoidal_ artery supplies principally the posterior
turbinated bones and septum nasi.


                BRANCHES OF THE EXTERNAL CAROTID ARTERY

Branches from the external carotid and the facial artery supply the
tongue and its muscles, the larynx, the lower jaw bone, the gums, and
the upper lateral facial region.

The external carotid (Fig. 62, No. _A_, 8) gives off the following
branches:

First, the =hyoid artery= (Fig. 72, No. 12) which supplies the inner
portion of the depressor mandibular and also the cornua of the os
hyoideum, and extends to the tip of the tongue.

Second, the =superior laryngeal artery= (Fig. 72, No. 16) which supplies
the sterno-brachialis and gives off branches which extend downward to
the trachea and to the esophagus. The main artery passes along the left
side of the esophagus and anastomoses with branches of the inferior
esophageal, forming collateral circulation in that region.

[Illustration:

  FIG. 62.

  _A._ Blood-vessels of the head. 1, The cerebellum. 2. The cerebrum. 3,
    The semicircular canals. 4, Sinus occipitalis superior. 5, Sinus
    temporalis sphenoideus. 6, Sinus transversus dexter. 7, Superior
    esophageal artery. 8, Carotis externus. 9, Lingual artery. 10, Sinus
    longitudinalis.

  _B._ Veins of the antero-inferior part of the head and neck. 1, The
    right carotid artery. 2, The left carotid artery. 3, Vena jugularis
    dexter. 4, Vena vertebralis dexter. 5, Transverse vein. 6, Vena
    cephalica dexter anterior. 7, Vena lingualis. 8, Vena cephalica
    posterior. 9, Vena facialis externa dexter. 10, Vena infrapalatina.
    11, Posterior nares. 12, Vena facialis interna. 13, Vena facialis
    externa sinister.

  _C._ The brain. 1, Medulla oblongata. 2, Cerebellum. 3, Optic lobe. 4,
    Cerebrum. 5, Longitudinal fissure. 6, Transverse fissure. 7,
    Olfactory nerve. 8, Optic nerve. 9, Optic commissure. 10, Motor
    oculi. 11, Patheticus. 12, Trigeminal, or trifacialis. 13, Abducens.
    14, Facialis. 15, Auditory, or acousticus. 16, Glosso-pharyngeus.
    17, Pneumogastric. 18, Spinal accessory. 19, Hypoglossus. 20,
    Hypophysis. 21, Crus cerebri. 22, Ganglion on superior nerve trunk.
    23, Spinal cord. 24, A pair of spinal nerves.
]

Third, the =lingualis artery= (Fig. 62, No. _A_, 9) which lies between
the mylo-hyoideus and the posterior part of the hyoid bone. It supplies
the tongue muscles. It passes to the median surface of the lower jaw
bone, where are given off small branches which enter the jaw and
anastomose with the inferior alveolar artery.

Fourth, the =Facial Artery=.—The facial artery divides into the
following branches:

The _auricular artery_ is given off near the articulation of the os
quadratum with the os zygomaticum. It is located at the outer auditory
canal, and its branches are distributed to the parotid region and to the
depressor mandibular, or digastricus, muscle.

The _external facial artery_ is located between the os quadratum and the
masseter muscle. It gives off a branch to the lower jaw bone and to the
skin of that region, and then passes to the lacrimal bone and supplies
branches to the commissure of the mouth, the auditory canal, the
masseter muscle, the three eyelids (upper and lower eyelids and the
membrana nictitans), the nose cavity, and the skin in the frontal
region. It communicates on the other side with the ethmoidal artery.

The _internal facial artery_ passes over and through the os
pterygoideum, supplies all the jaw muscles, and is continued as the
inferior alveolar artery.

The _inferior alveolar artery_ enters the canal of the lower jaw bone
along with the mandibular nerve. It is finally continued as the mental
artery, leaving the canal, and passing to the outer jaw surface.

The facialis continues as the _internal maxillary artery_.

The internal maxillary artery (Fig. 72, No. 15) supplies the pterygoid
muscle, the upper part of the pharynx, the commissure of the mouth, the
salivary gland region, the gums, and finally anastomoses with branches
of the spheno-maxillaris artery.


                    BRANCHES OF THE VERTEBRAL ARTERY

The vertebral artery is given off, dorsally near the thyroid gland, from
the carotis communis or from the carotid trunk. The vertebral artery
passes horizontally and dorsally into the canals formed in the
transverse processes of the cervical vertebræ. After it leaves the
carotid, it is divided into anterior and posterior branches.

The =posterior vertebral artery= passes in the canals of the transverse
processes of the fifth or sixth dorsal vertebra. It sends branches into
the vertebræ, into the spinal canal, and into the intercostal muscles
between the ribs and anastomoses with the intercostal arteries.

The =anterior vertebral artery= is larger than the posterior. It extends
laterally along the side of the neck in the foramen of the transverse
processes of the cervical vertebræ, and lies along the course of the
inferior vertebral vein and the deep imbedded trunk of the sympathetic
nerve. It continues to the head. In its passage it gives off to each
vertebral segment a dorsal and a ventral branch. Twigs from these
branches pass into the bodies of the vertebræ and the spinal canal,
giving nutriment to the bony structure and to the spinal cord and its
coverings. Other twigs are distributed to the muscles of the neck and
some finally anastomose with branches of the carotis communis. This
artery, reaching the head, gives off a long anastomosing branch which
passes between the atlas and posterior part of the occipital bone and
joins the ramus profundus and the occipital artery, thus again
communicating with the carotid artery. The remainder of the vertebral
artery is small and passes through the foramen magnum into the cranial
cavity where it anastomoses with terminal branches of the cerebral
artery. At the base of the neck and before the vertebral artery enters
the canal of the cervical vertebræ, it gives off the _arteria cervicalis
ascendens_, superior artery of the crop (Fig. 73, No. 18) which branches
out on the upper surface of the crop is also distributed to the neck
muscles, and later subdivides into the transverse cervical arteries
which supply the skin and the muscles of the base of the neck, and the
shoulder region.

On the ventral side of the neck there are given off two subvertebral
carotid arterial branches. They lie in a shallow furrow on the ventral
side of the cervical vertebræ and close to the median line.


                   BRANCHES OF THE SUBCLAVIAN ARTERY

The subclavian artery (Fig. 20, No. 13; Fig. 73, No. 11) gives off the
following branches:


1. =Sterno-clavicularis= (Fig. 73, No. 9) which originates on the upper
part of the subclavia, between the carotid artery and external thoracic
(Fig. 73, No. 3), divides into many branches. The sterno-clavicularis
gives off the _sternal artery_, which enters by the side of the
supra-coracoid muscle and the anterior rim of the sternum. It is
distributed to the inner surface and over the air-sac. Another outside
branch passes the posterior end of the crista sterna and supplies the
large breast muscles.

The _clavicular artery_ (Fig. 73, No. 8) accompanies the clavicle to the
shoulder-joint.

The _acromial artery_ is given off from the sterno-clavicularis on the
ligament near the shoulder-joint.

2. The =thoracic artery= branches from the subclavian artery (Fig. 70,
No. 4). The thoracic artery gives off the following branches:

The _internal mammary_, or _internal thoracic artery_ (Fig. 73, No. 16)
arises on the inner side of the sternum and extends downward and
backward, giving nutrient branches to the anterior vena cava and to the
diaphragm. At the point of the costo-sternal muscle it divides into an
inner and an outer branch.

The inner branch supplies the costo-sternal muscle and extends along the
ribs and along their juncture with the breast-bone. It finally extends
posteriorly, giving numerous branches to the abdominal muscles. The
outer branch is distributed in a similar manner, giving off branches to
the diaphragm and to the abdominal muscles, and anastomoses, on the
surface of the abdominal muscles, with the epigastric artery.

The _external thoracic artery_ (Fig. 73, No. 3), ramus superior,
supplies principally the large breast muscles.

The _inferior thoracic artery_, external ramus inferior, passes along
the outside of the pectoralis major muscle, extends downward, and gives
off the arteria thoracica longa (subcutaneous thoracic). This latter
artery supplies the skin of the breast region. Other branches are given
off to the muscles of the breast and to the skin of the region, and some
finally anastomose with the branches of the sternal artery.

3. The =axillary artery= (Fig. 73, No. 12) extends out of the thoracic
cavity along with the brachial nerve plexus. It gives off the
_subscapularis_ which supplies the muscles of the scapular region. The
axillary artery terminates as the _brachialis_ which passes between the
biceps brachii and anconeus muscles downward along the humeral shaft. It
gives off the anterior humeral circumflex artery and the brachialis
profunda artery (Fig. 68, No. 3). It gives off near the elbow-joint the
ulnar and radial arteries.

The _anterior circumflex humeral artery_ passes through the short head
of the biceps and gives off a branch to the biceps muscle, supplying the
insertional part of the breast muscles.


                  BRANCHES OF THE BRACHIALIS PROFUNDA

The brachialis profunda artery (Fig. 68, No. 3) continues as the
_posterior circumflex humeral artery_. This artery supplies the muscles
of the posterior part of the humerus, the skin of the wing, and the
muscles of the brachial region. The trunk of the arteria brachii
profunda passes downward along the anconeus muscle, supplying that
muscle and giving off the collateral ulnar artery. On the ulnar
olecranon it anastomoses with the recurrent ulnar, thus establishing, at
this region, collateral circulation. The rest of the brachialis sends
branches to the biceps muscle and to the skin of the upper arm, and
finally gives off the arteria collateralis radialis, which supplies the
condylo-ulnaris. It then anastomoses with the end branches of the
recurrent radialis artery.

The _radial artery_ (Fig. 67, No. 4) passes downward on the outer rim of
the forearm. It continues down to the carpal region, where it supplies
the muscles and the skin of the carpal region it gives off the recurrent
radial, which passes on the middle finger and finally anastomoses with
the collateral radialis artery.

The _ulnar artery_ (Fig. 68, No. 6 and 9) passes downward on the inner
surface of the ulna to the carpal region where it gives off a branch to
the wing plexus and divides into two branches, the smaller branch
supplying the thumb (Fig. 68, No. 7). This branch passes down the radial
side of the middle finger to the last joint of the second finger. The
larger (Fig. 68, No. 8) lies between the second and the third finger
bones, and passes through a slit between these two bones to the flexor
side of the hand and extends to the last finger-joint, supplying the
structures in the region. The ulnar artery gives off a small arterial
twig to the papilla of each large wing feather (Fig. 67, No. 6).

The _recurrent ulnar_ passes backward to the olecranon of the ulna and
supplies the muscles, the skin, the feathers, and other structures of
the region, and terminates in end collateral ulnar branches (Fig. 67,
No. 5).


                   BRANCHES OF THE POSTERIOR AORTA[7]

           ( Esophageal
           ( Intercostales
           ( Dorsal
           ( Lumbars
           ( Spermatics
           ( Renals
           ( Ovarian
           ( Celiac  ( Recurrent esophageal
           ( axis    ( Recurrent intestinalis  ( Recurrent ilio-colicus
           (         ( Posterior or recurrent sinister  ( Renalis
           (         ( Anterior or recurrent dexter     ( Splenics
           (         (                  ( Hepatic
           (         ( Hepatica dextra  ( Gastric
           (
 Posterior ( Sacralis media  ( Coccygeæ laterales
  aorta    (                 ( Coccygea media  ( Coccygeæ laterales
           (
           ( Anterior mesenteric  ( Recurrent ilio-celiacus
           (                      ( Recurrent superior hemorrhoidal
           ( Posterior mesenteric  ( Median hemorrhoidal
           (             ( Recurrent renalis
           (             ( Tibialis postica
           ( Ischiadica ( Tibialis antica ( Peroneal ( Anterior tibial
              plexus
           (             ( Arteria ovarialis
           ( Pudenda communis  ( Renalis
           (                   ( Hemorrhoidalis intima
           (                   ( Pudenda externa
           (
           ( Crural             ( Internal pelvic (umbilical)
           (  (External iliac)  ( Circumflex femoris
           (                    ( Femoralis

Footnote 7:

  Nomenclature used by Bronn.

The posterior aorta (Fig. 63, No. 2) passes backward along the inferior
part of the bodies of the dorsal and lumbo-sacral vertebræ. In the
thoracic cavity it lies dorsal to the esophagus. It gives branches
(_esophageal_) only to the esophagus during its passage as far as the
seventh dorsal vertebra. Following this point there are given of several
pairs of arteries which divide into a superior and an inferior branch.
The superior branch extends upward and anastomoses with branches of the
vertebral artery and other twigs coming from the _intercostal arteries_.
These latter arteries given off are small dorsal arteries. The inferior
branches extend downward between the ribs and supply the intercostal
muscles. The intercostal arteries do not take their origin from the
aorta in numerous and regular branches as in mammals; they consist
originally of but few vessels, which are multiplied by anastomoses with
each other and with the arteries which come out of the spinal canal. An
arterial plexus is thus formed around the head of each rib, from which a
vessel is sent to each of the intercostal muscles and ribs and are
continued into the muscles upon the outside of the body and its
integuments. The anastomosis of the intercostal arteries round the ribs
is similar to the plexus, which is produced by the great sympathetic
nerve in the same location. The _lumbar arteries_ are given off farther
posteriorly and along the lumbar region. The lumbar, like the dorsal
branches are given off in pairs. These arterial branches pass along the
thigh and the upper sacral vertebral region, and supply those parts.
Ventrally they are covered by the kidneys and pass into the abdominal
muscles. The posterior aorta gives off the _spermatic arteries_ and the
_ovarian artery_. In the male the former supply the testes. The ovarian
artery of the female gives off a twig to each calyx containing an ovum.
Each calyx is voluminously supplied with blood. Next the _renal
arteries_ are given off to the kidneys.

[Illustration:

  FIG. 63.—The vascular system injected. 1, The heart. 2, The posterior
    aorta. 3, The right brachio-cephalic artery. 4, The left
    brachio-cephalic artery. 5, The anterior mesenteric artery showing
    its many branches and anastomoses near and on the intestines. It is
    accompanied by branches of the mesenteric vein. 6, The rectal branch
    of the posterior mesenteric artery. 7, The duodenal loop and
    pancreas showing the pancreatic artery. 8, The anus. 9, The cloaca.
    10, The liver. 11, The lungs. 12, The right subclavian artery. 13,
    The right carotid artery. 14, The right anterior vena cava. 15, The
    subclavian vein. 16, The right jugular vein. 17, The carotid trunk.
    18, The posterior vena cava.
]

[Illustration:

  FIG. 64.—The splanchnic arteries, veins and nerves. 1, A portion of
    the left testes. 2, Adrenal gland. 3, Anterior lobe of kidney. 4,
    Heart. 5, Liver. 6, Second portion of the esophagus. 7,
    Proventriculus. 8, Gizzard. 9, Spleen. 10, Duodenal loop. 11,
    Pancreas. 12, Blind extremity of cæcum. 13, Floating portion of
    small intestine. 14, Rectum. 15, Cloaca. 16, Anus. 17, Celiac axis.
    18, Ureter. 19, Vas deferens. 20, Recurrent sinister artery. 21,
    Anterior recurrent dexter artery. 22, Arteria hepatica dextra. 23,
    Recurrent esophageal artery. 24, Recurrent intestinalis artery. 25,
    Ilio-colicus artery. 26, Anterior mesenteric artery. 27, Recurrent
    branches of the same. 28, Ilio-cœliacus artery. 29, Recurrent
    superior hemorrhoidal artery. 30, Posterior mesenteric artery. 31,
    Crural arteries. 32, Sacralis media artery. 33, Recurrent renalis.
    34, Middle renal lobe. 35, Posterior renal lobe. 36, Vena
    mesentericus communis. 37, Vena hemorrhoidalis. 38, Vena
    pancreatico-duodenalis. 39, Vena proventriculo-leinealis. 40, Vena
    portalis dextra. 41, Ischiadic nerve. 42, Thoracic sympathetic
    trunk. 43, Anterior splanchnic plexus. 44, Spinal nerves. 45,
    Posterior splanchnic nerve plexus. 46, Intestinal nerve trunk. 47,
    Vena renalis magna.
]

The =celiac axis= (Fig. 64, No. 17) originates near the seventh sternal
vertebra and to the right of the esophagus, breaks through the
diaphragm, and, near this point, gives off a recurrent esophageal (Fig.
64, No. 23). The celiac axis gives off three main branches: The anterior
or recurrent dexter, the posterior or recurrent sinister, the recurrent
intestinalis, all of which lie to the right of the spleen, under the
left lobe of the liver, and along the left side of the stomach. The
_recurrent sinister_ (Fig. 64, No. 20) gives arterial branches to the
proventriculus, the gizzard, the pyloris, and the left lobe of the
liver. The anterior or recurrent dexter (Fig. 64, No. 21) gives off a
renal artery and from four to six splenic arteries.

The _recurrent intestinalis artery_ (Fig. 64, No. 24) arises on the
posterior of the stomach within the duodenal loop, and supplies the
duodenum and the pancreas (Fig. 63, No. 7). It gives off a branch,
called the recurrent ilio-colicus (Fig. 64, No. 25), which supplies the
large intestines, including the cæca.

The _arteria hepatica dextra_ (Fig. 64, No. 22) is a branch from the
celiac axial trunk. It gives several branches to the right lobe of the
liver and to the gall-bladder. The gastric branches pass to the muscles
of the stomach. The anterior and posterior recurrent branches often
anastomose.

The =anterior mesenteric artery= (Fig. 63, No. 5; Fig. 64, No. 26)
originates from the posterior aorta near the generative glands. It is
directed downward, and divides into many branches which pass in the
mesentery toward the intestines. Recurrent branches (Fig. 64, No. 27)
are given off, which anastomose, forming mesenteric arches. From these
arches are given off branches which supply the intestinal walls.

The anterior mesenteric artery gives off the _recurrent ilio-celiacus_
(Fig. 64, No. 28) which is distributed to the cæca; other of its
branches are distributed to the small intestine.

The anterior mesenteric artery extends along the small intestine and
ends in the _recurrent superior hemorrhoidal arteries_ (Fig. 64, No. 29)
which anastomoses on the surface of the rectum with a branch of the
posterior mesenteric artery.

Branches from the anterior mesenteric artery also anastomose with
branches of the celiac axis.

The =posterior mesenteric artery= (Fig. 64, No. 30) is given off from
the posterior aorta posterior to the origin of the anterior mesenteric
and near the arteries of the thigh and is distributed to the lesser
mesentery supplying the large intestine. Branches of the superior
hemorrhoidal arteries anastomose with branches of the posterior
mesenteric artery. Branches from this source are called the _median
hemorrhoidal_ (Fig. 63, No. 6).

The posterior mesenteric artery (Fig. 64, No. 30) also gives off a long
branch to the cæca. Branches of the posterior mesenteric artery
anastomose with branches of the anterior mesenteric.

The =crural arteries= (Fig. 64, No. 31) are given off in a pair from the
posterior aorta. They pass through the mass of the lobes of the kidneys,
at about the median region, and extend out of the pelvic cavity in front
of the spine and ilio-pubic ligament.

[Illustration:

  FIG. 65.—Blood-vessels and nerves of the hind extremity. Inside view
    of leg. 1, Ischiadic nerve. 2, Ischiadic artery. 3, Posterior tibial
    vein. 4, Vena metatarsa dorsalis interna. 5, Vena metatarsalis
    plantaris profunda. 6, Vena cruralis. 7, Vena metatarsalis interna,
    vena magna. 8, Vena tibialis postica. 9, Vena metatarsa magna. 10,
    Nerves of the toes. 11, Vena metatarsalis dorsalis profunda.
]

The crural, or the external iliac artery, is divided into three branches
as follows:

First, the _internal pelvic_, or _umbilical artery_, is given off just
as the cruralis leaves the pelvic cavity. It passes, as a long vessel,
on the inner surface of the lumbo-sacral bones and supplies the
obturator internus muscle and extends into the umbilical region. It
gives off branches to the abdominal muscles, and, in the female, a
branch is distributed to the ligament of the oviduct.

Second, the _arteria circumflex femoris_, which passes between the
sartorius and vastus internus and extends dorsalward, supplies the
sartorius muscle, the vasti muscles, and the ilio-trochanteric region.

Third, the _femoral artery_, which passes beside the vena cruralis and
extends down the posterior surface of the thigh to the knee-joint,
supplies the upper thigh muscles with the exception of the adductor
muscles.

[Illustration:

  FIG. 66.—Blood-vessels and nerves of the posterior extremity. Outside
    view. 1, Anterior tibial artery. 2, Metatarsal artery. 3, Digital
    arteries. 4, Vena cutaneous crurus. 5, Ischiadic artery. 6, Vena
    cruralis. 7, Lateral cutaneous branch of the ischiadic nerve.
]

[Illustration:

  FIG. 67.—Blood-vessels and nerves of the fore limb. Outside view. 1,
    Median nerve. 3, Ulnar nerve. 4, Radial artery. 5, Recurrent ulnaris
    artery. 6, Twigs of ulnar artery to wing feathers.
]

The =ischiadic artery= (Fig. 69, No. 9) forms the main artery of the
posterior extremity. This artery, the largest vessel of that region, is
given off from the posterior aorta and passes ventrally over and between
two of the main lobes of the kidney. The continuation of the posterior
aorta is called the _sacralis media_ (Fig. 64, No. 32). The ischiadic
artery gives off a _recurrent renalis_ on the posterior lobe of the
kidney (Fig. 64, No. 33). On the left side it gives off a branch to the
oviduct and to the ligament of the oviduct. The main trunk leaves the
cavity with the ischiadic nerve (Fig. 65, No. 1) through a foramen
formed by the os ilium and the os ischium. It sends branches into the
adductor muscles of the upper and the lower thigh. It gives off
anastomotic branches which unite with those from the femoral artery. At
the flexure of the knee-joint it gives off two branches to that region
(Fig. 69, No. 10). It gives off another branch to the gastrocnemius
muscle and one to the flexor perforans digitorum. It terminates in the
anterior and posterior tibial arteries.

[Illustration:

  FIG. 68.—Blood-vessels and nerves of the fore limb. Inside view. 1,
    Vena humeri profunda. 2, Brachialis longus inferior. 3, Brachialis
    profunda. 4, Radial artery. 6, Ulnar artery. 7, Ulnar arterial
    branch to thumb. 8, Digital branch of ulnar artery. 9, Ulnar artery.
]

The first, the _tibialis postica_ (Fig. 69, No. 12) passes between the
gastrocnemius and the deep flexors giving off branches in its course to
the skin and to other parts, and disappears shortly below the
intertarsal joint.

The second, the _tibialis antica_ (Fig. 66, No. 1; Fig. 69, No. 11), is
often the larger of the two arteries. The anterior tibial artery gives
off branches to the knee-joint and to adjacent structures. It gives a
large branch to the head of the gastrocnemius muscle. It passes to the
posterior surface of the tibial head and gives off the peroneal artery,
which passes through the membrana interossea located between the tibia
and fibula giving branches to the anterior side of the membrane of the
patellar region of the knee-joint. It gives branches to the anterior
side of the lower thigh and finally terminates subcutaneously in the
anterior tibial plexus.

The main portion of the anterior tibial artery passes downward along the
posterior surface of the membrane located between the tibia and fibula,
and sends branches for the flexor digitorum communis et profundus. It
then breaks through the membrane, reaches the anterior side and there
communicates with the anterior tibial plexus. It gives off branches to
the muscles on the anterior side of the lower thigh and the skin, and
passes between the outer and the middle malleolus of the tarsal bones.
It passes to the plantar surface and divides between the toes. In
addition to the plantar branches there are given off dorsal branches
between the third and the fourth toes. These branches form the direct
continuation of the dorsal vessels of the anterior tibial plexus.

[Illustration:

  FIG. 69.—Blood-vessels and nerves of the femoro-tibial region. A
    section of the tibia removed.

  _A._ Veins, arteries and nerves dissected as in _B_.

  _B._ _V_, Vein. _A_, Artery. _N_, Nerve. 1, Vena poplitealis. 2, The
    three veins forming the vena poplitealis. 3, Vena femoris interna
    profunda. 4, Vena femoris anterior. 5, Vena cruralis. 6, Vena
    cutanea abdominalis femoralis. 7, Vena cutaneous cruralis. 8, Deep
    vein of the knee-joint. 9, Ischiadic artery. 10, Branches of
    ischiadic artery to flexure of knee. 11, Anterior tibial artery. 12,
    Posterior tibial artery. 13, Ischiadic nerve. 14, Trunk (a branch of
    the ischiadic) which gives off the superficialis peroneus and
    peroneus profundus. 15, Median branch of ischiadic nerve. 16,
    Superficialis peroneus. 17, Lateral branch of the ischiadic nerve.
]

The =arteria pudenda communis= (Fig. 70, No. 20) passes to the depressor
coccygeus muscle, gives off a branch to the caudal part of the kidney,
crosses the ureter, provides the ischio-pubic and pubio-coccygeus, or
depressor coccygis lateralis, muscles, and on the lateral rim of the
latter muscle it gives off the _arteria hemorrhoidalis intima_. This
artery passes to the bursa of Fabricius and to the end of the cloaca. It
enters into the ischio-coccygeus muscle, and divides into the _arteria
pudenda externa_, and in ducks, the _arteria profunda penis_. These
branches supply the vas deferens, the ureter, the cloaca, the penile
structure, and the muscles of these parts.

[Illustration:

  FIG. 70.—Blood-vessels of a Cornish cock. 1, The left pulmonary
    artery. 2, Right pulmonary artery. 3, Left brachio-cephalic artery.
    4, Left subclavian artery. 5, Left carotid artery. 6, Right
    brachio-cephalic artery. 7, Posterior aorta. 8, Posterior vena cava.
    9, Left pulmonary vein. 10, Right pulmonary vein. 11, Celiac axis.
    12, Anterior mesenteric artery. 13, Ischiadic artery. 14, Crop. 15,
    Superior artery of the crop and vein of same name. 16, Testicular or
    ovarian artery. 17, External iliac artery. 18, Intercostal nerve.
    19, Median sacral artery. 20, Arteria pudenda communis. 21, Anus.
    22, Vena hypogastrica. 23, Right vena hepatica magna. 24, Left vena
    hepatica magna. 25, Vena iliaca interna. 26, Vena iliaca communis.
    27, Vena iliaca externa. 28, Vena coccygo-mesenterica. 29, Vena
    umbilicalis. 30, Vena suprarenalis. 31, Origin of the pars renalis.
    32, Lumbar veins. 33, Vena epigastrica. 34, Lumbales (arteries). 35,
    Anterior division of the lumbo-sacral plexus. 36, Posterior division
    of the lumbo-sacral plexus. 37, Left anterior vena cava. 38, Right
    anterior vena cava.
]

=The Sacralis Media.=—The _median coccygeal artery_ (Fig. 70, No. 19)
forms the single extension of the sacralis media. It gives off lateral
branches between the caudal vertebræ which supply the dorsal muscles of
that region and the skin. The third pair are the largest. These are the
_arteriæ coccygeæ laterales_, and are located on the dorsal side of the
tail, they supply the tail glands and rudder feathers, the main tail
feathers, or rectrices. A small arterial twig is given off to the
papilla of each rectrix.


                           THE VENOUS TRUNKS

The venous blood enters the lungs from the right ventricle through the
two pulmonary arteries (Fig. 70, No. 1 and 2).

The two pulmonary veins (Fig. 70, No. 9 and 10) collect the arterial
blood from the lungs, and empty it into the left auricle.

There are three venæ cavæ which collect the systemic blood and empty it
into the right auricle. These venæ cavæ are two anterior (Fig. 70, No.
37 and 38) and one posterior (Fig. 70, No. 8).

Each anterior vena cava is formed by the union of a vena jugularis, a
vena vertebralis, and a vena subclavicularis (Fig. 63, No. 15).

[Illustration:

  FIG. 71.—Veins of the liver of a fowl. 1, Vena mesenterica communis.
    2, Vena portalis propria. 3, Anterior vena mesentericus. 4, Vena
    portalis dexter. 5, Vena portalis sinister. 6, Posterior vena cava.
    7, Celiac axis. 8, Base of the heart. 9, The liver. 10, Hepatic
    veins.
]

The jugular vein is formed by the union of the vena cephalica anterior,
and the vena cephalica posterior.

The jugular vein (Fig. 62, No. _B_, 3) passes along the side of the neck
and lies near the trachea, the esophagus, and the pneumogastric nerve.
Near the base of the skull the two jugular veins, the right and the
left, are connected by a transverse vein. By this anastomosis part of
the blood from the left jugular vein is sent into the right. Therefore
the right jugular vein is larger than the left. The jugular veins
collect the blood from the tongue region, the thyroid, the esophagus,
the trachea, the crop, and other structures along its course through the
cervical region.

The =vertebral veins= are divided into the anterior and the posterior,
or the inferior and the superior. The _anterior vertebral vein_ is
located in the cervical region and collects the blood from the brain and
the inner part of the head. The vertebral vein passes along the dorsal
side of the spinal cord.


                  BRANCHES OF THE VENÆ CAVÆ ANTERIORES

                         ( Venæ linguales
                         ( Vena occipitalis lateralis ( Vena
                            occipito-collores
                         ( Vena ascendenes lateralis
                         ( Venæ colli cutineæ
                         ( Venæ esophagealeæ
                         ( Venæ tracheales
            ( Vena       ( Vena subscapularis
            ( jugularis  ( Venæ glandularum thyroidearum
            ( ( ( Vena occipitalis ( Sinus foraminis
            ( ( ( interna ( occipitalis
            (            ( Vena          (
            ( ( vertebralis ( Vena vertebralis posterior ( Vena
               intercostales
 Vena cava  (            (               ( Vena vertebralis anterior
 anterior   (                                      ( Vena vertebralis
            ( Vena vertebralis lateralis dorsalis  ( Venæ intercostales
            (
            ( Venæ coronariæ
            ( Vena subclavicularis
            ( Vena thoracica interna  ( Vena intercostales

                ( Vena pharyngea superior
                ( Vena muscularis depressoris mandibularis
 Vena facialis  ( Vena muscularis colli anterior superioris
 communis       ( Vena lingualis
                ( Vena sublingualis et sphenoidea

The _posterior vertebral vein_ is located in the dorsal region, passes
backward and receives the blood from the dorsal neck region and from the
intercostal veins and from the vertebral segments and adjacent regions.

The anterior and the posterior vertebral vein form one trunk, the
vertebral vein, and this trunk empties into the vena jugularis just
before the subclavian and the jugular unite.

The =subclavian vein= collects the blood from the anterior extremities.
It unites with the vena jugularis of the same side.

The left vena cava receives the coronary veins from the heart.


                         THE VEINS OF THE HEAD


                 BRANCHES OF THE VENA FACIALIS INTERNA

The =vena facialis interna= (Fig. 62, No. 12) lies dorsal on the
pterygoid bone and receives the vena maxillaris, the vena ophthalmica,
the vena mandibularis interna, the venæ pharyngeæ superiores, and the
vena retis mirabilis temporale.

[Illustration:

  FIG. 72.—Blood-vessels and nerves of the abdominal cavity and hind
    extremity and head. 1, Vena renalis. 2, Vena intervertebrales
    sacrales. 3, Posterior aorta. 4, External iliac. 6, Ischiadic nerve.
    7, Ischiadic artery. 8, Arterial rete (plexus temporalis). 9,
    Ophthalmic artery. 10, Palatine artery. 11, Lingual artery. 12,
    Hyoid artery. 13, 14, External carotid artery. 15, Internal
    maxillary artery. 16, Superior laryngeal artery. 17, Superior
    esophageal artery. 18, Occipital artery. 19, Internal carotid
    artery.
]

The =vena maxillaris= comes out of the upper beak with the recurrent
trigeminus nerve and then passes backward between the jugular and
palatine bones. It lies medio-ventrally to the eyeball and communicates
at this point with the ophthalmic vein. It is covered ventrally with the
pterygoid bone. The maxillary vein collects the blood from the gland of
Harder, the upper beak, and receives blood from the _vena
supra-palatina_ and from the lower jaw bone and the external mandibular
vein. It also receives blood from the external sublingual vein, and the
sublingual gland. It follows the inner rim of the jaw bone. The
maxillary vein receives an anastomosing branch from the cutaneous facial
vein, at a point near the commissure of the mouth.

[Illustration:

  FIG. 73.—Photograph of blood-vessels and nerves of the thorax. 1, Vena
    sternalis. 2, Vena thoracico-externa. 3, External thoracic artery.
    4, Coracoid bone. 5, Sternum. 6, Shoulder-joint. 7, Humerus. 8,
    Clavicularis artery. 9, Sterno-clavicularis artery. 10,
    Thoracico-humeralis artery. 11, Subclavian artery. 12, Axillary
    artery. 13, Brachialis profundus artery. 14, Ulnar artery. 15,
    Radial artery. 16, Internal mammary artery. 17, Superior vein of the
    crop. 18, Superior artery of the crop. 19, Brachial nerve plexus.
    20, Anterior division of brachial nerve plexus. 21, Posterior
    division of brachial nerve plexus.
]

The =vena ophthalmica= lies close to the point where the olfactory nerve
passes out of the cranial cavity. The largest branch it receives is the
recurrent ophthalmo-temporalis, which accompanies the lateral side of
the optic nerve. It collects the blood from the base of the brain, from
Harder’s gland, from the eye muscles, from the inner eye, the nose, the
lacrimal gland, the skin of the frontal region, and the comb.


                     BRANCHES OF THE VENA JUGULARIS

                                                         ( Vena
                                                            maxillaris
                                                         ( Vena
                                                            ophthalmica
                                      ( Vena facialis ( Vena mandibularis
                                         interna
                                      ( interna ( Vena retis mirabilis
                                         temporalis
                   ( Vena cephalica ( ( Venæ pharyngeæ superiores
                   (  anterior or     (
                   ( facialis ( ( Vena facialis cutinea
                   ( communis ( ( Vena temporalis
                   ( ( Vena facialis ( Vena auricularis
 Vena jugularis ( ( externa ( Vena palpebralis
  or cephalica ( ( Vena transversus
  communis ( ( Vena retis mirabilis temporalis
                   ( Vena subclavia
                   ( Venæ vertebrales
                   (                  ( Sinus cranii et cerebri
                   (                  ( Vena carotis
                   (                  (
                   ( ( Vena auris ( Sinus foveæ cerebelli
                   ( ( ( Vena occipitalis externa
                   ( Vena cephalica   ( Vena jugularis prima
                   (  posterior       ( Vena occipitalis
                                      ( Vena lingualis

                          ( Vena mandibularis externa
          Vena maxillaris ( Vena sublingualis externa
                          ( Vena supra-palatina

          Vena ophthalmica ( Vena ophthalmo-temporalis, recurrent

          Vena facialis communis ( Vena cephalica externa

          Vena occipitalis externa ( Vena occipitalis interna

          Vena retis mirabilis temporalis ( Vena spheno-temporalis

          Sinus foveæ cerebelli ( Sinus occipitalis externa

The trunk of the internal facial vein receives the blood of the
=internal mandibular vein=. The internal mandibular vein emerges from
the alveolar canal of the inferior jaw bone and receives branches from
the muscles of mastication.

The =vena retis mirabilis temporalis= passes out of the eye cavity and
lies between the internal facial vein and the external facial vein, and
passes around the os quadratum and the os pterygoideum. It receives
veins from the outer ear region, lacrimal gland, eyelids, and the
spheno-temporalis.

The =venæ pharyngeæ superiores= are the veins on the dorsal surface of
the pharynx. These veins form the small plexuses which unite with the
two trunks of the facial veins. This forms an anastomosis between the
left and the right facial veins.


                  BRANCHES OF THE EXTERNAL FACIAL VEIN

The vena facialis externa (Fig. 62, No. _B_, 9) lies behind the quadrate
bone and is partly covered ventrally by the inner extension of the lower
jaw bone. It collects the blood principally from the upper region of the
cranium and the face, including the comb.

The =vena facialis cutinea= receives branches from the muscles in the
region of the jaw, the lower jaw bone, the muscles of the eyelids, the
frontal region, and the anastomotic branches from the vena maxillaris.

The =vena temporalis= is made up of veins from the skin of the temporal
region, the masseter and the tongue muscles, and from the sides of the
upper throat region.

The =vena palpebralis= is made up from veins from the three eyelids and
the temporal region near the eye. Its trunk passes laterally over the
temporo-mandibularis ligament. The vena palpebralis collects blood from
the lacrimal gland, the eyelids, and the outer ear region.

The following veins empty into the trunk of the =vena facialis
communis=: venæ pharyngis superiores, vena muscularis depressoris
mandibulæ, vena muscularis colli anterior superioris, vena lingualis et
hyoidea. The right terminal branches of the vena lingualis empty into
the vena cephalica posterior.

The venæ pharyngis superiores and vena lingualis et hyoidea collect
blood from the muscles of the tongue and posterior tongue region.

The _vena lingualis et hyoidea_ (Fig. 62, No. _B_, 7) collects the blood
from the muscles of the tongue region, the lower tongue glands, and the
upper throat region.

Between the two trunks of the vena facialis communis and anterior to the
entrance of the vena cephalica posterior there is an anastomosis, the
vena transversus (Fig. 62, No. _B_, 5). Through this anastomosis which
lies crosswise the two jugular veins are influenced in different ways.
At this point both jugular veins are of the same size. The anastomotic
branch lies crosswise. Through this anastomosis the right receives some
blood from the left head region indicating that the blood flows from
left to right. This, as stated before, makes the left jugular vein the
smaller.


                BRANCHES OF THE VENA CEPHALICA POSTERIOR

The left vena cephalica posterior (Fig. 62, No. _B_, 8) communicates
with the transverse vein (Fig. 62, No. _B_, 5). The left receives the
smaller veins of the skin region, the esophagus, and the trachea. These
vessels communicate with their fellow of the opposite side and with the
vertebral vein of the same side, which causes a gradual reduction of the
size of the jugular vein.


               BRANCHES OF THE VENA OCCIPITALIS EXTERNUS

               (                  ( Venæ choroideæ
               ( Sinus            ( Venæ cutaneæ et frontales
               (  longitudinalis  ( Venæ nasales
 Vena          (                  ( Venæ ophthalmiæ
  occipitalis  (
  externus     (                  (               ( Sinus occipitalis
               ( Sinus ( Sinus ( Sinus temporo-sphenoideus
               (  semicircularis  (  transversus  ( Venæ cerebellares
               ( ( ( Sinus petrosus sphenoideus

                  Sinus petrosus sphenoideus  ( Retis mirabile temporalis
                  Sinus temporo-sphenoideus ( Sinus annularis venosus
                     basilaris
                  Sinus foraminus occipitalis  ( Venæ medullares

             ( Venæ cerebrales
 Sinus ( Vena cerebralis basilaris ( Sinus venosus annularis anterior
  venosus    (
  annularis  (
  basilaris  ( Vena ophthalmica
             ( Vena medullaris mediana longitudinalis

The vena cephalica posterior (Fig. 62, No. _B_, 8) is formed from the
veins of the sinuses of the cranium, the brain, the vena auris, the vena
jugularis prima, the vena carotis, and the vena occipitalis. It collects
most of the blood from the cranium and the posterior part of the head
and from the tongue.


                     THE VENOUS SINUSES OF THE HEAD

The =sinus longitudinalis= (Fig. 62, _A_, 10) extends from the dorsal
median line of the internal occipital protuberance to the olfactory
nerve. It collects the blood from the choroidea of the brain and from
the skin of the frontal region. It receives laterally the veins of the
nose, the vena ophthalmica, and the sinus transversus.

The =sinus occipitalis= (Fig. 62, No. _A_, 4) forms the continuation of
the transverse sinus. It is located in the posterior cerebral cavity,
and is wing-shaped, extending both to the right and to the left.

The =sinus foraminis occipitalis= a continuation of the sinus
occipitalis, lies transversely on the ventral side of the cranial cavity
and receives the veins from the medulla oblongata. One branch passes
through the os occipitalis basilare, and then extends sidewise to the
foramen magnum and anastomoses with the vena occipitalis.

The =sinus transversus= (Fig. 62, No. _A_, 6) extends in a pair from the
internal occipital protuberance between the cerebrum, cerebellum, and
the corpus quadrigeminum. It receives vessels from the upper surface of
the cerebellum. The sinus has three branches, all of which empty into
the sinus semicircularis.

The =sinus semicircularis= extends along the dorsal petrosal rim,
anterior to the inner ear, and from this point backward. Near the
foramen magnum it passes through the os occipitale and empties into the
external occipital vein.

The =vena occipitalis externus= extends near the foramen magnum,
surrounds the basis occipitalis, and receives the semicircular sinus and
through the semicircular sinus the blood from the sinus transversus.

The =sinus petrosus sphenoideus=, passing in company with the occipital
sinus, extends from the transverse sinus to the cavity near which the
trigeminus lies. The sinus dividing into two branches, one of these
extends to the hypophysis and unites with the basal veins of the brain;
the other passes with the rete out of the cranial cavity along with a
branch of the trigeminus, and communicates with the rete mirabile
temporale.

The =sinus temporo-sphenoideus= (Fig. 62, No. _A_, 5) extends forward
and outward from the transverse sinus, and, between the corpus
quadrigeminum and the cerebrum, unites with the sinus venosus annularis
basilaris.

The =sinus venosus annularis basilaris= lies in the region of the optic
nerve and surrounds the hypophysis, forming a complete circle. It
receives small vessels from the cerebrum, the corpora quadrigemina, and
anteriorly the longitudinal basilar vein or vena basilaris media, of the
cerebrum, which comes out of the anterior annular venous sinus. The
anterior annular venous sinus surrounds the base of the olfactory
nerves. It communicates with the sinus petrosus sphenoideus, which
emerges from behind the optic lobe, the sinus temporo-sphenoideus, which
emerges from in front of the optic lobe, and posteriorly the median
longitudinal vein of the medulla oblongata or vena basilaris. Laterally
and anterior to the optic lobe it receives the vena basilaris lateralis,
and also a branch of the vena ophthalmica.

The blood received by the =sinus annularis basilaris= comes from the
brain cavity through three pairs of veins, as follows: first, the two
ophthalmic veins which pass through the posterior orbital wall between
the olfactory and the optic nerve; second, two other branches of the
ophthalmica which pass with the optic nerve; third, two veins which pass
through a foramen by the side of the sella turcica to the hypophysis
together with the carotis cerebralis, and then leave the cerebral cavity
ventrally, at which point they are called the venæ carotes. These last
accompany the cerebral artery backward, and pass through a foramen in
the base of the cranium. Each one then passes through the cranial wall
close to the external auditory canal, and empties into another vein in
the posterior region of the head.

The =sinus fovæ hemispherii cerebelli= lies in the hollow between the os
petrosum and the semicircular canals. It receives blood from the
external occipital sinus and from the cerebellum, and empties into the
vena auris interna.


                       VEINS OF THE BRAIN CAVITY

The =vena auris interna= passes through a bony canal along the outer rim
of the posterior semicircular canal and then along the external
semicircular canal. It receives vessels from the labyrinth, and extends
along the posterior rim of the tympanum to the outer ear canal.

The =vena occipitalis interna=, extending from the sinus foraminis
occipitalis, passes through the side of the atlas and divides near the
condyle into two branches. One of these branches the internal occipital,
forms the root of the vena vertebralis, and the other empties into the
vena occipitalis externa.

Near the outer and upper part of the condyle it forms two large veins
and collects the blood from the vena occipitalis media. These veins
collect the blood from the rectus capitis anticus, and communicate with
the vena cephalica anterior.

The =vena occipitalis externa=, sometimes called the vena occipitalis
collateralis, extends from the vena auris, and receives vessels from the
neck region. It receives on the side of the occipitoatloid joint the
vena occipitalis interna. The vena occipitalis externa forms a junction
with the vena vertebralis emptying into the transverse vein.


                         THE VEINS OF THE NECK


                     BRANCHES OF THE VENA JUGULARIS

The trunks of the vena jugularis or vena cephalica communis pass
subcutaneously on both sides near the trachea and the esophagus. Near
the height of the thyroid gland they almost touch the carotid artery.
They then cross, dorsalward, the trunk of the subclavian artery, and in
their course receive the vertebral vein and unite with the subclavian
vein toward the side of the vena brachiocephalica. The union on the
right side lies to the right of the anterior aorta, and the union on the
left side lies to the left of the pulmonary artery.

The jugular vein (Fig. 18, No. 4) receives in its course the following
veins:

The =venæ linguales= (Fig. 62, No. _B_, 7), which at times empty into
the vena cephalica posterior.

The =vena occipito-collares=, which arises on the ventral side from the
muscles of the neck and the vertebræ; empties into the vena occipitalis
lateralis and also communicates with the vena jugularis by anastomoses.

The =venæ ascendentes laterales=, which collect blood from the lateral
sides of the neck.

The =venæ colli cutineæ=, which enter the jugular vein laterally. The
upper branches are directed crosswise, and are shorter than the lower
ones. The lower branches are located near the thorax, are directed
upward, and anastomose by fine terminal twigs. Plexuses are frequently
formed in the inner side of the skin of the neck.


                     BRANCHES OF THE VENA SUBCLAVIA

                                                   ( Vena profunda
                                                      ulnaris
                                ( Vena brachialis ( Vena profunda
                                   radialis
                ( Truncus venæ  (                  ( Vena profunda humeri
                (  axillaris    (
                (               ( Vena basilica or cutinea ulnaris
                (
                (                  ( Vena cutinea abdomino-pectoralis
 Truncus venæ   ( Vena pectoris    ( Vena infrascapularis anterior
  subclaviæ     (  externa         ( Vena thoracica externa
                ( Vena coracoidea
                ( Vena sternalis

The =venæ esophageæ= are numerous smaller veins formed in closely woven
plexuses in the region of the esophagus along the neck. Some pass upward
and some downward.

The =venæ tracheales= are located on the supero-lateral side of the
trachea and along the edge of the lateral tracheal muscle. They have
numerous anastomoses transversely with the longitudinal vein of the
cervical region, anteriorly with the vena lingualis, and on the left
side with the left jugular vein.

The =vena subscapularis= passes along the median line of the scapula to
the side of the jugular vein, and anastomoses with the vertebral vein.

The =venæ glandularum thyroidearum= are several small, short veins
coming from the thyroid gland.

The =vena vertebralis=, originating near the atlas, is a continuation of
the internal occipital vein. The internal occipital vein receives the
bulk of the blood from the brain and communicates with the lateral veins
of the cervical region and collects blood from the cervical vertebra.
The vertebral vein accompanies the vertebral artery and the deep
sympathetic nerve trunk in the vertebral canal. The vein either leaves
this canal with the vertebral artery at a point near the last two
vertebral nerve trunks of the brachial plexus, or it leaves the canal
one vertebra in front of the vertebral artery.


                     THE VEINS OF THE DORSAL REGION

The =vena vertebralis lateralis dorsalis= collects blood from the
cervical vertebræ, from the dorsal vertebræ, and from the intercostal
region.

The blood from the neural canal, including the spinal cord, is collected
in one long vein extending from the head to the tail on the upper side
of the cord. This vein has sinus-like expansions. Between each two
vertebræ it anastomoses with the vertebral vein on each side. In the
lumbo-sacral region these anastomotic branches empty into the
hypogastric veins.

The =vena intercostalis= is formed in the costal region and anastomoses
with the vein extending longitudinally between the capitulum and the
tuberculum of the rib.

The =vena vertebralis posterior= at the height of the first and the
second dorsal vertebræ, empties into the main trunk of the vertebral
vein. Its lower roots come out near the side of the kidney, and unite,
forming a large ascending trunk uniting with the vena vertebralis
anterior forming one large trunk, which extends into the chest cavity.

The posterior vertebral vein also receives a large vein from the skin of
the outer tarsal region and a few vessels from the muscles of the outer
abdominal and the outer costal region, from the skin, from the
pectoralis muscles, and from the shoulder region.


                          VEINS OF THE THORAX


                     BRANCHES OF THE VENA SUBCLAVIA

The =vena thoracica externa= (Fig. 73, No. 2) is made up of veins mainly
from the pectoral group of muscles. The posterior branch anastomoses
with the vena cutinea. Its anterior branch is made up mainly of branches
from the furcular region. It empties into the vena pectoralis externa
and the vena pectoralis externa empties into the vena subclavia.

The =vena coracoidea= comes out of the region of the shoulder-joint,
passes downward along the inner surface of the coracoid, and receives
small branches from the walls of the arteria brachia cephalica and from
the pericardium.

The =vena sternalis= (Fig. 73, No. 1) is made up of two branches. The
outer branch comes from the muscles of the subclavian region passes over
the cristi sterni, medially, to the sterno-coracoid joint and into the
breast cavity, where it receives the inner branch, which drains the
inner surface of the breast-bone.

The =vena thoracica interna= empties into the vena cava anterior. It
extends from the abdominal muscles where it communicates with the
epigastric vein. It then passes on the inner side of the thoracic cavity
close to the breast-bone and receives many intercostal veins.

The =vena cava sinistra= receives first, the _vena proventricularis
communis_, which collects the blood from the walls of the
proventriculus, and second, the vena coronaria cardis magna. This latter
vein originates close to the apex of the heart and collects blood
principally from the walls of the left ventricle. It connects in the
left sulcus transversus with the vena cardis superior and ends at the
base of the left upper vena cava. Its exit is not guarded by a valve.
The veins of the right ventricle are partly on the surface. They collect
blood along the sulcus transversus dexter and enter directly into the
right ventricle. The veins of the front part of the heart are small.
They collect behind the sulcus coronalis and end either directly into
the right auricle or into the vena cardis magna.


                         VEINS OF THE FORE LIMB

The =vena radialis profunda= accompanies the radial artery on the dorsal
anterior rim of the index-finger and passes, on the dorsal side, over
the carpal region. It passes through the interosseous ligament between
the ulna and the radius, and reaches the ventral surface of the arm. At
this point it passes upward and anastomoses with the vena ulnaris. It
collects the blood from the skin of the anterior wing region and the
flexor muscles of the anterior arm. It empties into the vena brachialis.

The =vena humeri profunda= (Fig. 68, No. 1) emerges at the height of the
elbow, and collects blood from the skin of the dorsal surface of the
wing. It also receives veins from the muscles of the posterior side of
the upper arm. It passes subcutaneously and dorsally over the dorsal
portion of the humerus in company with the external radial muscle and
passes with it around the external part of the humerus between the long
and short heads of the triceps. It takes a diagonal course to the
shoulder cavity and at that point empties into the brachial trunk.

The =profundus ulnaris= originates at the volar surface of the hand,
proceeds in company with the ulnar artery, and sends on the base of the
hand small anastomotic veins to the vena cutanea ulnaris or basilica. It
passes along the anterior arm and between the flexor carpi ulnaris and
the pronator profundus muscle to the elbow-joint. On the median surface
of the biceps it passes upward and anastomoses with the radial vein. The
ulnar vein, in the region of the elbow-joint, receives a large lateral
branch which extends around the end tendon of the biceps and anastomoses
above with the vena basilica.

The =vena basilica= or cutanea ulnaris is a long vein which originates
from the subcutaneous dorsal surface of the index-finger. Near the base
of the hand it receives an anastomosing branch from the vena radialis
and the vena ulnaris, and then passes upward along the posterior rim of
the ulna. It receives numerous branches from the roots of the flight
feathers. It crosses below the elbow-joint and reaches the volar surface
of the arm. It receives a large branch from the ulnar vein, and then,
passing in a diagonal and median direction to the triceps, extends to
the shoulder cavity where it empties into the axillary vein.

The outer breast veins unite forming a trunk which crosses ventrally to
the subclavian artery, and empties into the subclavian vein.

The vena cutanea abdomino-pectoralis collects the blood from a large
skin area of the abdomen, the upper thigh, the breast, and the
intercostal region. In the skin of the abdomen it forms a network.


                         BRANCHES OF THE ILIACS

                                   ( Vena metatarsalis ( Vena
                                      metatarsalis
                      ( Vena ( interna or magna ( plantaris profunda
                      (  tibialis  ( Vena tibialis antica
                      ( postica ( Vena metatarsalis ( Venæ metatarsales
                           (       (  externa
                           (
                           ( Vena ( Vena metatarsalis dorsalis profunda
           ( Vena ( tibialis ( Vena metatarsalis dorsalis interna
           (  poplitealis  (  antica    ( Vena peronealis
           (               ( Vena cutanea cruralis
           (               ( Venæ surales
 Vena      (
  iliaca   (            ( Vena cutanea abdominalis femoralis
  externa  ( Vena       ( Vena femoralis interna profunda
           (  cruralis  ( Vena femoralis anterior
           (            ( Vena epigastrica

The main trunk passes in the median abdominal line forward and then
upward, along the outer edge of the pectoralis major, over the first
sternal rib; receives blood from the infrascapular vein, and empties
into the pectoralis externa.

The =vena brachialis= is located in the middle of the humerus and the
triceps muscle. It is formed by the vena ulnaris, and the vena radialis.
It passes with the median nerve and the brachial artery over the inner
surface of the humeral joint. Posterior to the humeral head it receives
the vena profunda humeri. At the shoulder cavity it receives the vena
cutanea ulnaris or vena basilica.

The trunk of the axillary vein is very short and is formed by the veins
of the shoulder and the wing. The deeper wing veins accompany the large
arterial and the nerve trunks.


                  BRANCHES OF THE VENA ILIACA INTERNA

                                       ( Vena intervertebralis lumbalis
                     ( Pars truncalis  ( Vena renalis magna
                     (                 (
                     ( ( ( Vena hypogastrica caudalis sinistra
                     ( ( Vena renalis ( Vena hypogastrica caudalis dextra
                     (                 (                ( Vena portalis
                     ( ( Vena coccygea ( Vena cutanea et pudenda
 Vena iliaca ( ( Vena coccygea mesenterica
  interna or         (                ( Vena cutanea pubica
  vena hypogastrica  ( Pars caudalis  ( Vena cutanea caudalis
                     (                ( Vena pudenda  ( Vena spermatica
                     (                ( Vena caudalis muscularis
                     (               ( Venæ sacrales
                     ( ( Venæ intervertebrales sacralis ( Venæ renales
                     (               ( Venæ renales
                     ( Pars renalis  ( Vena ischiadica
                                     ( Vena obturatoria
                                     ( Vena suprarenalis externa ( Azygos
                                        sacralis


                        THE POSTERIOR VENA CAVA

The posterior vena cava (Fig. 63, No. 18; Fig. 70, No. 8) has its origin
in the posterior half of the body of the bird, somewhat to the right of
the posterior aorta, near the anterior lobe of the kidney, by the union
of the right and the left vena iliaca communis. It receives the blood
from all of the posterior half of the body including the posterior
limbs, of the visceral organs, of the abdominal and the pelvic cavity.
The posterior vena cava passes dorsally through the right lobe of the
liver and through the diaphragm and ends in a short, broad trunk on the
posterior dorsal side of the right auricle of the heart. Its opening
into the heart is guarded by two half-moon shaped valves. The basal part
of the trunk reaches from the right auricle of the heart to the upper
anterior rim of the liver where it receives three large trunks, first,
the right and second, the left vena portalis hepatica magna, and third,
smaller vessels from the liver substance.


                  THE VEINS OF THE POSTERIOR EXTREMITY

In the skin region on the inner sides of the toes near their bases the
small veins collect into five metatarsal veins. The largest vein
collects the blood from the first, the second, and the third toe, passes
up the tarsus and is called the vena metatarsalis interna, or vena magna
(Fig. 65, No. 7). It is located just beneath the skin on the inner
surface of the metatarsal bone. It passes in a circle, around the
condyle of the tibia and becomes the =vena tibialis postica= (Fig. 65,
No. 3 and 8). The vena tibialis postica passes under the tendon Achillis
and the tendon of the flexor digitorum brevis, lies subcutaneously upon
the latter, and reaching the knee-joint crosses over the upper surface
of the ischiadic nerve and becomes the =vena poplitealis=, at which
point it receives the vena tibialis antica.


                  BRANCHES OF THE VENA CAVA POSTERIOR

             ( Vena ovariana
             ( Venæ testiculæ
             ( Vena proventricularis communis
             ( Vena suprarenalis revehentis
             ( Vena portalis magna sinistra
             ( Vena portalis magna dextra
             ( Venæ innominatæ
             ( Venæ hepaticæ
 Vena cava   ( Vena cardis coronaria magna
  posterior  ( Vena proventricularis inferior
             (              ( Vena iliaca interna  ( Vena hypogastrica
             (              ( Vena iliaca externa  ( Vena renalis
             (              ( Vena suprarenalis externa
             ( Vena iliaca  ( Vena ischiadica
             (  communis    ( Vena renalis
             (              ( Vena intervertebralis lumbalis
             (              ( Vena renalis magna

            ( Vena mesenterica communis  ( Vena coccygo-mesenterica
 Vena       (                            ( Vena mesenterica anterior
  portalis  ( Vena pancreatico-duodenalis
  dextra    (                                 ( Vena proventricularis
            ( Vena proventricularis lienalis  ( Vena splenica

 Vena coccygo-mesenterica  ( Vena hemorrhoidalis

On the dorsal side of the metatarsus are two veins. The =vena
metatarsalis dorsalis profunda= (Fig. 65, No. 11), which extends under
the tendon of the extensors of the toes, along with the artery and the
nerve. It collects the blood from the third and the fourth toe and in
the middle of the metatarsus receives the =vena metatarsalis dorsalis
interna= (Fig. 65, No. 4), which connects the vena metatarsalis dorsalis
profunda and the vena magna. The two dorsal veins anastomose with the
vena magna, at the intertarsal joint. They pass transversely under the
ligament and form the main trunk of the vena tibialis antica which lies
close to the anterior surface of the tibia. Near this point there is
formed a plexus of veins which again form a trunk and communicates with
the vena peronealis and enters between the tibia and fibula with the
tibialis antica. It extends along the flexure of the knee and the
posterior part of the lower thigh.

The =vena metatarsalis externa= passes subcutaneously on the outside of
the fourth toe and the metatarsus, and above the intertarsal point joins
the tibialis postica.

The =vena metatarsalis plantaris profunda= (Fig. 65, No. 5) lies on the
ventral side of the foot and forms several anastomosing arches with the
other veins of the toes. Below the intertarsal joint it enters the vena
metatarsalis magna (Fig. 65, No. 9).

The =vena cutanea cruralis= (Fig. 69, No. 7) originates at the height of
the tarsal region and passes subcutaneously on the outer posterior
surface of the lower thigh region to the vena poplitealis.

The =venæ surales= or inferior muscular branches of the vena poplitealis
consist of many veins. One branch comes from the region of the shank and
from the gastrocnemius muscle; another as a main branch from the
posterior surface of the lower thigh; and a third from the outer surface
of the muscles and skin of the upper thigh. The three branches together
with the anterior and posterior tibial (Fig. 69, No. 2) unite at the
flexure of the knee forming the vena poplitealis (Fig. 69, No. 1).

In the region of the upper thigh, between the knee and the abdominal
cavity, the following four veins form the vena cruralis: (Fig. 66, No.
6; Fig. 69, No. 5). First, the =vena cutanea abdominalis femoralis=
(Fig. 69, No. 6) which comes out of the side of the abdominal wall,
draining the skin of the inner surface of the upper portion of the
thigh, the adductor muscles, and the region of the abdominal and the
breast border. It crosses the ischiadic artery in a diagonal direction,
and enters the vena cruralis in the middle of the crural region.

Second, the =vena femoralis interna profunda= (Fig. 69, No. 3) forms a
communication between the end of the suralis near the knee. It lies on
the median portion of the flexor cruris internus muscle.

Third, the =vena femoralis anterior= (Fig. 69, No. 4) is formed from
branches from the sartorius and adjacent structures, and anteriorly
empties into the crural vein near where the latter enters the abdominal
cavity.

Fourth, the =vena epigastrica= (Fig. 70, No. 33) is formed by branches
from the abdominal wall and branches from the walls of the abdominal
air-sacs. It passes along the median surface of the os pubis and ends
into the vena cruralis near the spine of the ilio-pubica or at a point
where these join with the vena hypogastrica.


          VEINS OF THE CAUDAL REGION AND OF THE PELVIC CAVITY

The vena iliaca interna or the vena hypogastrica (Fig. 70, No. 22)
collects most of the blood from the tail. The vena iliaca interna
collects most of the blood from the pelvic cavity, and the adjacent
intestines. It unites with the vena iliaca externa (Fig. 70, No. 27) and
receives the vena renalis magna and forms the trunk of the vena iliaca
communis (Fig. 70, No. 26).

The =vena coccygea= originates between the coccygeal vertebræ, and
collects the blood from the region of the tail, including the tail
feathers, the tail muscles, the tail gland, and the skin of the region.
These small collecting vessels form a trunk on each side of the coccyx.
The right and the left pass laterally, each one taking up a vena cutanea
et pudenda, and frequently anastomosing with the vessels on the other
side. These often unite into one vessel. Both trunks are connected by a
transverse, or anastomotic, vessel. At this anastomosis there empty into
it the vena coccygea mesenterica and the vena portalis. There also
communicate at this point the right and the left hypogastrica caudalis.
In its course it is partly imbedded in the kidney and passes anteriorly
to the vena iliaca communis. This circle is called the arcus
hypogastricus. Thus the veins of the abdominal cavity have many
anastomoses forming many arcs, making possible two outlets for the
blood.

The azygos sacralis empties into the arcus at about its middle. From
here it extends forward to the inside and under the kidney and empties
into the vena suprarenalis externa.

The =vena cutanea pubica= originates on the lower portion of the
abdomen, collects the blood from the muscles of the distal part of the
ischium, and enters the pelvic cavity between the ischium and the ilium.
It joins with the vena cutanea caudalis.

The =vena cutanea caudalis= originates from branches which drain the
skin and other parts of the ventral coccygeal region. The vena cutanea
pubica also communicates with the vena caudalis muscularis and with the
vena pudenda, thus forming the caudal trunk of the vena hypogastrica.

The =vena pudenda= originates in the walls of the cloaca in the region
of the generative organs.

A small =vena spermatica= accompanies the lower end of the vas deferens
and the ureter, and empties medially into the vena pudenda.

The pars renalis of the vena hypogastrica extends from the middle of the
arcus to the union of the vena hypogastrica and the vena cruralis.

The =vena hypogastrica= communicates with the pars renalis. The vessels
that empty into the pars renalis are as follows:

The =venæ sacrales= collect blood from the dorsal wall of the abdominal
cavity and enter the pelvis through the foramen sacralis. They pass
between the pelvic wall and kidney, and at times pass through the kidney
tissue. They empty into the pars renalis of the hypogastric arch.

The =venæ intervertebrales sacrales= (Fig. 72, No. 2) originate in the
region of the roots of the plexus of sacral nerves and pass through the
kidney substance or on the dorsal surface and empty into the pars
renalis.

The =venæ renales= (Fig. 72, No. 1) are very numerous and originate in
the kidney substance, forming two main and several minor branches, which
pass posteriorly, and empty partly into the vena hypogastrica, partly
into the vena renalis magna, and also into the vena intervertebralis;
other branches empty into the trunk of the iliaca communis.

The =vena suprarenalis externa= (Fig. 70, No. 30) is located near the
anterior rim of the kidney and is connected with the vena hypogastrica.
It also receives on the medial side, short branches which come out of
the upper kidney surface and sacral vertebræ.

The =vena ischiatica= originates by the union of several venous branches
which come from the muscles of the pelvis and upper thigh region. The
ischiatic vein enters the pelvic cavity along with the ischiatic nerve
and artery, and communicates with the vena hypogastrica at about the
level of the anterior lobe of the kidney. It is always smaller than the
vena cruralis.

The =vena obturatoria= originates mainly from vessels from the obturator
muscles. It enters the pelvic cavity through the obturator foramen.
Another branch is sometimes found which comes out of the inner surface
of the peritoneum which covers the obturator muscles and the walls of
the abdominal air-sacs and empties between the vena ischiatica and the
vena vertebralis into the vena hypogastrica.


               VEINS OF THE TRUNCUS VENA ILIACA COMMUNIS

The =vena intervertebralis lumbalis=, which comes out of the lumbar
region, the spinal canal, the lumbo-sacral nerve plexus, and several
small venous branches from the lobes of the kidney. It passes dorsalward
through the kidney and empties into the iliac vein. There are also
communications with the vena intervertebralis thoracica.

The =vena renalis magna= (Fig. 64, No. 47) forms the main descending
vein to the middle and posterior lobes of the kidney. It lies ventrally
and mesially on the middle lobe and partly on the inner part of the
posterior lobe. It sometimes has on each side two main trunks. The vein
receives some small vessels out of the anterior kidney lobe, also other
small veins from that part of the peritoneum which covers the kidney,
from the rectum and finally small veins from the ureter.


               VISCERAL VEINS OF THE POSTERIOR VENA CAVA

The =venæ testiculæ=, or the vena ovariana drain the blood from the
testicles of the male and ovary of the female. The size of these veins
change with the enlargement of the testes or of the ovary during
reproductive activity.

The =venæ suprarenales revehentes= are short, thick trunks coming from
the adrenal glands. The left empties into the left side of the posterior
vena cava and the right into the right dorsal side. These receive veins
from the testicles in the male and from the ovary in the female.

The =vena proventricularis inferior= drains the stomach wall. One branch
of this vein enters the left side of the posterior vena cava; the other
enters the vena proventricularis communis, which in turn empties into
the trunk of the anterior vena cava sinistra.

The =venæ hepaticæ= consist of one large and several small veins from
each lobe of the liver, and empty into the posterior vena cava.

Some small vessels come from the pericardium and the peritoneal covering
of the liver, and pass in the mediastinum to the trunk of the posterior
vena cava.

In the region of the vena portalis:

The liver receives almost all the blood from the stomach, the
intestines, the pancreatic gland, the spleen, partly from the liver
itself, and partly from the abdominal air-sacs. This blood enters into
the liver through the vena portalis dextra, the vena portalis sinistra,
and the vena portalis propria.

In both lobes of the liver these veins divide into numerous small
branches and collect again into two large short trunks, the vena
hepatica magna dextra (Fig. 70, No. 23), coming out of the right lobe of
the liver and the vena hepatica magna sinistra (Fig. 70, No. 24) coming
out of the left lobe. These two vessels empty inferiorly into the
posterior vena cava.

The vena portalis dextra receives the blood from the vena mesenterica
communis.

The =vena mesenterica communis= (Fig. 64, No. 36) receives the blood
from the vena coccygo-mesenterica (Fig. 70, No. 28) which comes from the
arcus hypogastricus and receives the vena hemorrhoidalis (Fig. 64, No.
37). This drains the cloaca and the bursa of Fabricius, and it also
receives veins from the rectum and from the base of the cæca.

The =vena mesenterica anterior= (Fig. 71, No. 3) accompanies the
anterior mesenteric artery, and collects the blood from numerous vessels
from the small intestine.

The =vena pancreatico-duodenalis= (Fig. 64, No. 38) comes out of the
duodenum and the pancreas, along the right side of the stomach and along
both cæca.

The =vena proventriculo-lienalis= (Fig. 64, No. 39) comes out of the
dorsal side of the proventriculus on the left side of the gizzard,
passes along the hilus of the spleen, and takes up several splenic
veins.

The =vena portalis dextra= (Fig. 64, No. 40; Fig. 71, No. 4) receives a
vein near the base of the gall-bladder. This branch enters the right
lobe of the liver and unites with the vena portalis sinistra.

The =vena portalis sinistra= (Fig. 71, No. 5) enters the left lobe of
the liver and there forms a sinus. It receives vessels which come from
the muscles of the gizzard, the inferior vena proventricularis, and from
the proventricular wall.

The =vena portalis propria= receives small veins which come out of the
walls of the abdominal air-sacs and from the fat of the abdominal walls.

The =vena umbilicalis= originates in the umbilical region and empties
into the vena hepatica magna sinistra at a point where it comes out of
the liver (Fig. 70, No. 29). This is the remains of an embryonal vein
which collected all the blood of the yolk sac, passed on the left side
of the large intestine to the body, took up the vena mesenterica and
ended as the vena umphalo-mesenterica.


                          THE LYMPHATIC SYSTEM

The peculiarity of the lymph vessels is that they are associated with
organs in which lymph cells are formed.

The lymphatic system consists of the lymph vessels and the cell-forming
organs. In some instances the cell-producing organs are lymph follicles
and in others lymph glands. For the most part the glands are replaced by
plexuses which in many places surround the blood-vessels.

The lymph of birds is similar to that of mammals. The larger lymph
vessels are similar to the veins, although the walls are always thinner.
Its tunica intima is rich in elastic fibers and has a layer of
endothelial cells on the inner side. The tunica media is formed of rings
of smooth muscle fibers. The adventitia is composed of loose connective
tissue.

The lymph vessels frequently form plexuses. The large lymph trunks
follow the course of the larger blood-vessels, and frequently surround
the arteries. All the lymph vessels of the body, exclusive of the lymph
of the caudal region, form into a large trunk which originates on both
sides of the celiaca communis and passes upward along the side of the
abdominal aorta, reaching a point anterior to the celiaca. By receiving
many vessels in this region it forms a plexus around the aorta, and
finally divides into two vessels, the right and the left, ducti
thoracici.

The lymph vessels of the left side of the head, the neck, and the lung,
and the left wing, and also lymph vessels of the proventriculus and the
throat enter into the left ductus thoracicus. They accompany the jugular
vein and are closely associated with the thyroid gland.

The right thoracic duct receives the lymph veins from the right cervical
lymph vein, and the right side of the head, the neck, the lung, and from
the right wing.

After the right cervical lymph vein has passed through the right thyroid
gland, it divides into two branches, one branch emptying into the right
thoracic duct and the other into the vena cava dextra.

The lymph vessels of the liver, the stomach, the pancreas, and the
duodenum enter near the root of the arteria celiaca into the large lymph
trunk. The lymph vessels of the remainder of the intestines, of the
kidney, and of the generative organs empty farther caudally.

The lymph vessels of the intestines take up the emulsified fat. This
emulsion in birds is colorless. The vessels pass upward along the
mesenteric arteries. There are no mesenteric glands. These vessels form
a plexus around the arteria celiaca. The lymph vessels of the posterior
extremities accompany the artery, especially the anterior iliaca
externa, and empty into the thoracic duct at the point of the anterior
iliaco-communis.

The lymph vessels in birds are numerous. The lymph glands are few. They
are only visibly found in the anterior breast and the neck region, and
sometimes in the wings. Lymph follicles are numerous in the intestines.

The thin walls of the lacteals, of the lymph vessels, and of the
thoracic duct are made up of two tunics, the inner being the thinner and
weaker.

The lymphatics of the foot unite to form the vessels along the sides of
each toe. In palmipedes there are anastomosing branches which pass from
the lateral vessels of one toe to those of the adjoining toe, forming
arches in the uniting web of the foot. These branches form a small
plexus at the anterior part of the digito-metatarsal joint, from which
pass three or four lymph vessels. The anterior and internal branches
accompany and form a network around the blood-vessels. The posterior and
external branches receive the lymphatic vessels from the sole of the
foot. They then ascend along the metatarsus and form, at its proximal
articulation, a close network from which vessels pass along the tibial
region, forming a plexus around it as far as the middle of the leg. From
this there arises two branches. The smaller passes along the anterior
part of the depression between the tibia and the fibula, as far as the
knee-joint, where it joins the other branch, which accompanies the
blood-vessel. The trunk formed by the union of these two vessels
accompanies the femoral vessels. Forming plexuses in its course, it
receives tributary vessels from the adjacent muscles. The iliac trunk
accompanies the femoral vein into the abdominal cavity, entering just in
front of the anterior end of the pubis. At this point it receives
branches from the lateral parts of the pelvis and then separates into
two branches. The posterior vessel receives some lymph from the anterior
lobes of the kidney, and from the ovary, or testis, and communicates
anteriorly with a branch formed by the lymph vessels adjacent to the
anterior mesenteric artery, and posteriorly with a large vesicular
plexus surrounding the aorta and its branches. This plexus receives the
lymph from the renal plexus and from those accompanying the arteria
media.

There are two sacral or pelvic vesicles which are situated at the angle
between the tail and the thigh in the posterior part of the abdominal
cavity. Each vesicle is a trifle more than a half inch long and a
quarter inch wide, and is shaped somewhat like a kidney bean. They have
muscular coats with striated fibers. These sacs are called “lymph
hearts.”

The anterior division of the femoral lymphatic trunk accompanies the
aorta, on which it forms a plexus with the branches of the opposite
side, and with the intestinal lymph vessels. These vessels commence from
a continuous plexiform network located between the mucous and the
muscular coat of the intestine. They are larger at this point than where
they leave the intestine to pass through the mesentery. They accompany
the trunk of the anterior mesenteric artery and form a plexus around it.

Before reaching the region of the aorta, the intestinal lymphatic
vessels communicate with the posterior division of the femoral trunk and
with the lymph vessels of the ovary or of the testis. After passing to
the region of the aorta they receive vessels from the pancreas and the
duodenum, and terminate around the celiac axis with the lymphatics of
the liver, the proventriculus, the gizzard, and the spleen, forming a
rather voluminous plexus (Lauth).

The aortic plexus represents the receptaculum chyli and gives origin to
two thoracic ducts, mentioned above, which passing on each side of the
bodies of the vertebræ, pass one right and one left, over the lungs,
from which they receive lymph vessels, and terminate after receiving the
lymph vessels of the wing, into the jugular vein of their respective
sides. The left thoracic duct, before emptying into the vein, receives
the trunk of the lymphatics of the left side of the neck, and the right
duct that of the right side of the neck, each tributary collecting lymph
from all the structures of its side.

The lymphatics of the wing follow the course of the brachial artery,
forming a plexus around it. These vessels are well developed in the
elbow region. The principal trunk, following the humerus, receives
collateral branches in its upper third. This vessel, when nearing the
chest, receives two or three large lymph vessels from the pectoral
muscles, and a branch which accompanies the brachial plexus.

The lymph vessels of the head accompany the branches of the jugular
vein, collecting the lymph from the structures of the head and the neck.

The lymphatic vessels communicate at the anterior and posterior oblique
anastomosing vessels. At the lower part of the neck each trunk receives
a vessel, which accompanies the carotid arteries. Further on they are
provided with a lymph gland which rests on the jugular vein.




                      THE BLOOD AND ITS FUNCTIONS


The special function of the blood is to nourish all the tissues of the
body, and in this way to aid growth and repair. It furnishes material
for the purpose of the elaboration of body secretions; it supplies the
organism with oxygen; and it carries away carbon dioxid and other effete
material. Blood is constantly in circulation.

Blood is red, opaque, and is, in the fowl, quite viscid. The exact tint
of the blood depends on whether it is drawn from an artery or from a
vein. Blood from a vein has a purplish tinge while that from an artery
is a bright scarlet. The color of blood is largely due to pigment in the
erythrocyte, called hemoglobin.

The _reaction of the blood_ is alkaline, due to the phosphate and the
bicarbonate of soda. The alkalinity of the blood is reduced by work.
This is due to the formation of sarcolactic acid in the muscle. The odor
of blood is due to volatile fatty acids. Each kind of fowl has its own
peculiar odor. The taste of the blood is saltish, due to a small amount
of sodium chlorid it contains.

The blood consists of the following substances:

First, the unorganized part, or fluid, the liquor _sanguinis_ or
_plasma_. It contains in solution proteids, extractives, mineral matter,
and gases. The gases are held in loose chemical union.

The liquor sanguinis constitutes fully 66 per cent. of the volume of the
blood. It is albuminous in nature and contains a small amount of
coloring matter of a fatty nature. It holds in solution three
proteids—fibrinogen, serum globulin, and serum albumin.

Second, the organized parts, or the cellular structure (Fig. 74, Nos. 1
to 21). The cells float in the plasma and consist of three groups: the
erythrocytes, or red blood cells, the leucocytes, or white blood cells,
and the thrombocytes.

=Erythrocytes.=—The average number of red cells (Fig. 74, No. 21) of the
domestic fowl range between 3,000,000 and 4,000,000 per cubic
millimeter. The red blood cells are flattened and elliptical in shape,
and possess an oval elliptical nucleus. The average length is ¹⁄₂₁₀₀
inch and the diameter ¹⁄₃₈₀₀ inch, or 7 to 8 micra in diameter and 12 to
13 micra in length. However the diameters vary in different kinds of
birds. The cytoplasm is yellow and glassy, and the nucleus takes basic
stains and appears somewhat picnotic.

=Thrombocytes.=—The thrombocyte (Fig. 74, No. 19) is of about the same
length as the erythrocyte but somewhat narrower. The nucleus is round,
stains purple with the Wright’s stain, and the chromatin material is
somewhat diffused. The diameter of the nucleus is nearly equal to that
of the cell. The cytoplasm is pale and may show vacuoles near the
nucleus. They may contain small circumscribed red structures. They vary
somewhat in size and shape. There are in the domestic fowl between
45,000 and 55,000 per cubic millimeter.

=Leucocytes.=—There are, in the blood of the hen, 28,000 to 35,000
leucocytes per cubic millimeter. The leucocytes may be divided into five
distinct types. These are as follows:

_Polymorphonuclear leucocytes_ with eosinophilic rods (Fig. 74, No. 2)
are round and have a diameter about equal to the length of the
erythrocyte. The nucleus is polymorphous; that is, it has two or more
lobes. The nucleus stains a pale blue, and the chromatin is diffused.
The cytoplasm is colorless with bright red staining spindle-shaped rods.
There are 28 to 32 per cent. of this type of cell in the blood of the
hen.

[Illustration:

  FIG. 74.—Blood cells of the fowl. _Wright’s stain._ From a S. C. Rhode
    Island Red cockerel. 1, Basophile (mast cell) with lilac staining
    spherical granules. 2, Eosinophile with rod-shaped acidophile
    bodies. 3 and 4, Eosinophiles with acidophile staining round
    granules. 5, Eosinophile ruptured. 6, Mononuclear leucocyte with
    vacuoles in the cytoplasm. 7 and 9, Transitional leucocytes (first
    stage). 8, Mononuclear leucocyte. 10, 11, and 12, Small lymphocytes.
    13 and 14, Large lymphocytes. 15, A lymphocyte. 16, Lymphocyte
    (nucleus centrally located). 17 and 18, Transitional leucocyte. 19,
    Thrombocyte. 20, Neutrophile (polymorphonuclear). 21, Erythrocytes.
]

Polymorphonuclear leucocytes with eosinophilic granules (Fig. 74, No. 3
and 4) are of about the same shape and size as the preceding. The
nucleus is similar to the former except that it may appear slightly
picnotic. The cytoplasm stains not at all or faintly blue; it contains
round or spherical granules which stain a dull red. There is from 4 to 6
per cent. of this type of eosinophiles found in the domestic fowl.

_Lymphocytes_ are round in shape and of about the diameter of the width
of a thrombocyte (Fig. 74, No. 11). The nucleus is round, staining
somewhat purple, and contains a diffused chromatin material. The
cytoplasm exists in only small amounts; it lies to the side of the
nucleus and stains a pale blue. This is the small lymphocyte. A similar
cell but much larger also exists. This is the large lymphocyte (Fig. 74,
No. 13). There is from 40 to 44 per cent. of the lymphocytes in the
blood of the fowl. The small lymphocytes are most abundant.

_Large mononuclear cells_ (Fig. 74, No. 6) either round or oval, in
shape, whose diameter may be about that of an erythrocyte and at times
much larger. The nucleus may be round, oval, or irregular, and at times
rather crescent or U-shaped (Fig. 74, No. 17). The cytoplasm is abundant
and completely surrounds the nucleus. The cytoplasm stains a paler blue
than the nucleus. Both taking the basic stain as do the lymphocytes.
These constitute 18 to 20 per cent. of the cells of the blood.

_Mast cells_ or _basophiles_ (Fig. 74, No. 1) are of about the same size
and shape as the eosinophiles. The nucleus is round or oval, and stains
a very pale blue. The cytoplasm is colorless, mostly to one side of the
nucleus, and contains round or spherical purple staining granules. This
type of cell constitutes from 2 to 4 per cent. of the white cells of the
blood.

=Structure of the Red Blood Cell.=—The red blood cell is composed of a
spongy stroma holding in its meshes the red coloring matter. The stroma,
or framework, of the erythrocyte consists principally of nucleo-albumin;
it contains lecithin, cholesterin, and salts. The red matter consists of
an albuminous crystalline substance called hemoglobin, which forms about
90 per cent. of the total solid matter of the dried corpuscle. Each red
cell offers a certain absorbing surface for oxygen. As the blood
circulates through the delicate walls of the lungs and the air-sacs, it
takes up oxygen; the blood at the same time delivers to the air carbon
dioxid which has been brought from the tissues where active cell
metabolism has been going on. This oxygen taken up by the erythrocyte
forms a loose chemical union and is known as oxy-hemoglobin. In this
form it is carried to the tissues of the body where it is given up by
the erythrocyte to the tissues where oxidation is going on.

_Hemoglobin_ is a crystallizable proteid substance containing carbon,
hydrogen, oxygen, nitrogen, sulphur, and iron.

=Formation of the Cells of the Blood.=—The red blood cells are formed in
the red marrow of the bone.

Polymorphonuclear leucocytes are formed in the red marrow of the bones,
and the lymphocytes in the lymph glands and lymph follicles.

The bird carries a normal body temperature of 105° to 107° F. The
average temperature of 50 mature hens and cocks was 106.8° F. The blood
is of a deep red color.

=Composition of the Blood.=—The average composition of the blood of the
domestic fowl as given by Owen, is as follows:

               Whole shed blood:
                       Water                   780 parts
                       Clot                    157 parts
                       Albumin and salts        63 parts
                                                   —————
                                              1000 parts

               Moist blood cells:
                       Average total weight       456.69
                       Water                      342.52
                       Solid matter                97.50

               Plasma:
                       Total weight         543.30 parts
                       Water                495.72 parts
                       Solid matter          30.72 parts

Blood when drawn and allowed to stand soon coagulates. In the blood of
birds this process is very rapid, the blood coagulating, in most
instances, in about one-half minute. Blood coagulates only in the
presence of calcium salts.

During life, the liquor sanguinis is termed plasma; but after it has
been shed from the body and coagulation has taken place, the liquid
residue is called serum. Serum is plasma with its modifications as the
result of coagulation, and as this latter process is brought about by
the production of fibrin, we may say that serum is plasma minus
fibrin-forming elements.

The proteids of the serum are serum globulin, serum albumin, and a
ferment produced as the result of coagulation. As fibrinogen is used up
in the process of coagulation, it is not found in the serum, but there
is in the serum a proteid known as fibrino-globulin. This is produced
from fibrinogen during the process of fibrin formation. The following
tabulation gives a clear idea of the difference between the proteids of
plasma and of those of serum:


                           Proteids of Plasma

                             Fibrinogen
                             Serum globulin
                             Serum albumin


                           Proteids of Serum

                     Serum globulin
                     Serum albumin
                     Fibrin ferment (nucleoproteid)
                     Fibrino-globulin

Fibrinogen is the precursor of fibrin.

The fibrin of the blood clot of the bird is soft and very lacerable. The
serum is usually yellow.


                THE FATE OF THE ERYTHROCYTE OF THE FOWL

The power of vascular endothelium to ingest red blood corpuscles has
been studied by Keys.

When bacteria or other minute foreign bodies are injected into the blood
stream of pigeons, they are rapidly withdrawn from the circulation into
the tissues of the liver and of the spleen. The foreign bodies are noted
to be contained within cells of a distinct type, which is found in both
liver and spleen. This type of cell contains, in addition to the foreign
substances injected, much yellow pigment, and when tested for iron by
Pearl’s method gives a positive Prussian-blue reaction.

In such specimens there is a display of contrast to other tissues. There
is an extensive content of cells possessing the distinct tone of
Prussian-blue iron reaction. These cells are distributed rather evenly
throughout both the spleen and the liver, but more numerously in the
liver.

In the liver, under low-power magnification, these cells appear as blue
patches, sharply differentiated from the red-stained parenchyma. These
cells are larger in their greater diameter than the liver cells. They
vary much in size and form. They bear a constant relationship to the
venous capillaries, and often appear to occupy the lumen of the vessels.
Under higher magnification it is noted, however, that each cell is an
integral part of the endothelial intima lining of the capillaries. They
are therefore fixed tissue cells, engaged by one of its surfaces upon
the reticulum of the vessel wall, with a free surface bulging a greater
or less degree into the lumen of the vessel. The attached surface of the
cell follows exactly the line of the vessel wall. These cells are
similar to those described for mammals by Kupffer and are called Kupffer
cells or stellate cells. In the fowl Keys proposes the name hemophages.
The nucleus of the hemophage stains a deep garnet with the carmine used
in the above-given technic, and contains two or three very distinct and
intensely stained nucleoli. In the hemophages, which are more nearly
flat, the nucleus appears like those of the typical endothelial cells;
whereas in the protruding hemophages of greater bulk, the nucleus is
more vesicular and is irregularly pyramidal in form. Rarely two nuclei
are found in one cell. Within this cell may be seen vacuoles of the
cytoplasm which contain red blood corpuscles. These blood corpuscles
have been phagocyted from the circulating blood stream. Approximately
one-third of the intimal cells are hemophages. Each hemophage displays
evidence that it contains, or has recently contained, one or more red
blood cells. The cell body of the hemophage has no fixed morphology, but
changes from time to time according to its phase of phagocytic activity.
In a stage which the hemophage has recently ingested a red blood cell,
the cell body bulges out into the lumen of the vessel and the nucleus is
crowded to one side. At this time the red blood cell appears as those in
the blood stream and possesses the characteristic staining reactions.
The nucleus of the red blood cell stains deep reddish brown and the
cytoplasm an even yellow bronze. In the next stage the cytoplasm of the
hemophage gives a diffuse Prussian-blue reaction. Then in hemophages
which represent later stages there are various stages of disintegration
and digestion of the red blood cell. The first changes of the phagocyted
red blood cell is hemolysis, the hemoglobin escaping into vacuoles of
the cytoplasm of the phagocytic cell, leaving the nucleus-containing
stroma distinctly outlined. The stroma may retain the original ovoid
form or may become spherical; the nucleus in such instances remains
ovoid. Gradually, both the stroma and nucleus lose their staining
reaction until finally the vacuoles contract about a small indistinct
remnant of the nucleus, which in its turn ultimately disappears. During
this latter process the size of the hemophage gradually decreases. The
hemoglobin, which has escaped into the cytoplasm of the hemophage, is
seen to undergo a series of changes. At first the greater part of the
pigment does not give the iron reaction but retains its yellow-bronze
tone with erythrosin and occupies vacuoles of various sizes. Later the
contents of the vacuoles give the iron reaction and with increasing
intensity. Later there is a gradual decrease in the staining reaction
indicating that the iron gradually disappears from the cells which
extracted it from the red blood cells it digests. As a summary we find,
that these cells take care of the worn out red blood cells. They devour
them; hemolyze them, destroying the stroma and nucleus; split the
hemoglobin and free the iron; and then finally return to their normal
form.

The spleen contains the same type cells, but they are fewer in number.
For the most part they are confined to the pulp cords and have no such
evident relation to the vessel wall, or lumen, as in the liver.

The function of the cells of the spleen are essentially the same as
those in the liver.

Iron freed from the worn out red blood cells is not retained by the
cells freeing it, nor is it found in the bile. It does not occur
elsewhere in the tissues of the liver and spleen. It is possibly
discharged into the blood stream, and transported to the hemapoietic
tissues. Cells which hemolyze red blood cells and liberate the iron are
to be seriously thought of in connection with bile formation since
bilirubin is approximately, if not identical with, iron-free hematoidon.




                               NEUROLOGY


=The Nervous System.=—The nervous system is an apparatus by means of
which animals appreciate and become influenced by impressions from the
outer world. Animals react on these impressions, and thus are enabled to
adapt themselves to their environment. This system is the organic
substratum of life, sensation, and motion. Broadly stated, the nervous
system connects the various parts of the body with each other, and to
coördinate the parts into a harmonious whole in order to carry on the
bodily functions methodically and to control the physiological division
of labor throughout the organism.

The nervous system consists of two parts. The first is the
_cerebro-spinal system_, which comprises the central nervous axis,
including the brain and the spinal cord, and the peripheral nerves,
including the cranial and the spinal nerves. The second is the
_sympathetic nervous system_. The two parts of the system are closely
linked together, and both terminate in peripheral nerve endings,
including those of special sense, of sensation, and of motion.

The cerebro-spinal nerves especially preside over the special senses,
motion and sensation; and the sympathetic over the digestive, the
pulmonary, and the vascular apparatus.

From a structural standpoint, the nerve system consists of cell elements
peculiarly differentiated from all other tissue cells in that their
protoplasm is extended in the form of processes, often to great
distances from the nuclear region. The cell elements are held in place
by supporting tissue and receive an abundant blood supply; they are
partly of ectodermal and partly of mesodermal origin.

The cell element of the nerve system, called a _neurone_, is the
developmental, structural, and functional unit of the nervous system. It
is a single cell presenting unusual structural modifications. It
comprises not only the nerve cell body with its numerous protoplasmic
processes, or dendrites, but also the axone, which may vary in length
from a fraction of a millimeter to fully half the bird’s length. The
bulk of the axone is many times the bulk of the cell body.

Certain non-medullated axones are surrounded by a delicate, homogeneous,
nucleated sheath, called the neurilemma, or sheath of Schwann.


                           THE CRANIAL NERVES

The cranial nerves have their origin in the brain and leave the cranial
cavity in pairs. They are numbered numerically from before backward,
there being twelve pairs in all. The following is a tabulation according
to their number, name, and function:

  No.        Name                                  Functional Nature
    I. Olfactory         Smell-sense
   II. Optic             Visual-sense
  III. Oculomotor        Motor to muscles of eyeball and orbit
   IV. Pathetici         Motor to superior oblique muscle of eyeball
    V. Trifacial         Mixed: Sensor to face and tongue. Motor to face
   VI. Abducentes        Motor to External rectus of eyeball
  VII. Facial            Motor to muscles of head and face
 VIII. Auditory          Hearing-sense
   IX. Glosso-pharyngeal Mixed: Tongue, pharynx and muscles of throat
    X. Vagus             Mixed: Sensori-motor to respiratory tract and part of alimentary tract
   XI. Spinal accessory  Motor to muscles of pharynx, neck and heart
  XII. Hypoglossal       Motor to muscles of the tongue

=Olfactorius.=—Nervus olfactorius (Fig. 75, _C_, 16). This is the nerve
of smell, one of the nerves of special sense. The organ of smell
consists of five layers as follows:

First, a layer of olfactory fibers extending in different directions and
consisting of a dense plexiform arrangement of the axones of the
olfactory cells. From this layer the fibers pass into the layer of
olfactory glomeruli where their terminal ramifications mingle with the
dendritic terminals of cells lying in the more dorsal layers, to form
distinctly outlined spheroidal or oval nerve fiber nests, the _olfactory
glomeruli_.

Second, a fine granular layer of basic substance containing round
cellular structures, the _stratum granulosum_.

Third, broader granular, or molecular layer, having on its inner surface
a row of large pyramidal cells which are both small and large and which
send their dendrites into the olfactory glomeruli. Their points are
directed outward.

Fourth, a layer of round cells tightly pressed together and measuring
about 5 microns in diameter. Between these cells are very fine nerve
fibers.

[Illustration:

  FIG. 75.—The brain of a hen. Photograph.

  _A._ Upper surface of the brain. 1, Medulla oblongata. 2, Calamus
    scriptorius. 3, Cerebellum. 4, Optic lobes. 5, Transverse fissure.
    6, Longitudinal fissure. 7, Upper surface of the left cerebral lobe.
    8, Upper surface of the right cerebral lobe. 9, Lateral pillar of
    the cerebellum.

  _B._ The posterior surface of the eyeball. 10, The sectioned surface
    of the optic nerve.

  _C._ The inferior surface of the brain. 11, Corneo-scleral juncture.
    12, The cornea. 13, The sclera. 14, The optic nerve. 15, The optic
    chiasm. 16, The olfactory lobes. 17, The medulla oblongata. 18,
    Tuber cinererum et infundibulum.
]

Fifth, a layer of epithelial cells.

The peripheral fibers and the nerve cell layers near the hemispheres
disappear so that the basic substance of the trabecula with the
hemispheres form the entire lobe mass. On the lower surface of the
hemispheres there is a long bundle of nerve fibers which enter into the
substance of the olfactory lobes and there disappears. These fibers are
medullated. Non-medullated fibers enter into the makeup of the olfactory
trunk.

The original center of the olfactory nerve is not in the hemisphere, but
in the same location as the optic nerve. This nerve trunk consists of
very fine non-medullated fibers. The nerves of smell are therefore not
peripheralistic nerves. The nerve fibers are distributed to the mucous
surface of the turbinated bones. Toward the front they form an expanded
prolongation.

The olfactory nerve, as it emerges from the cone-like anterior tip of
the cerebrum, is of considerable thickness and extends along with the
median dorsal artery of that region above and to the inside of the
orbit, under the thin bony structure. Before its termination into the
posterior turbinated bones, it is crossed by the superior maxillary
division of the fifth pair of cranial nerves. It extends as far as the
pituitary membrane of the turbinate bones upon which its filaments are
distributed radially.

=The Opticus.=—The nervus opticus (Fig. 75, No. _C_, 14) the second
cranial, is the nerve of sight. The optic lobe, or tuberculum bigeminum
lies at the base of the brain on each side of the optic tract.

From the optic lobes the two trunks pass forward along the under surface
of the cerebri, forming the optic chiasm at the hypophysis (Fig. 75, No.
_C_, 15), at which point the nerve fibers originating from the right
side pass to the left, and _vice versǎ_. From the chiasm the true optic
nerves pass forward to the posterior surface of the eyeball. They are
composed of a bundle of very fine, marrow-like nerves. These fibers
enter into the ganglionic cells of the retina. By removal of the finely
adherent neurilemma, the optic nerve is seen to be composed of parallel,
longitudinal lamellæ, the margins of which are mostly free on one side.

=The Motor Oculi.=—The motor oculi (Fig. 62, No. _C_, 10), the third
cranial nerve is a motor nerve. It originates close to the base of the
brain behind the position of the hippocampus of mammals on the inner
side of the crus cerebri, and also on the inner somatic column close
below and somewhat aside from the aqueduct of Sylvius. The nerve leaves
the brain cavity through a distinct foramen near the foramen opticum,
and supplies the following eye muscles: first, after entering the orbit,
it sends a branch upward to the inferior portion of the inferior rectus;
then, it gives off the thick ramus ciliaris. The trunk then extends
under the optic nerve and passes forward to innervate the inferior
rectus, the internal rectus, and the inferior oblique. A ciliary
ganglion forms on the trunk.

=The Patheticus.=—(Fig. 62, No. _C_, 11) is a small motor nerve,
originating close to the sulcus centralis, in the circle of the center
brain over the valve of Vieussens, between the posteriors of the optic
lobes. It extends in a dorsal direction between the cerebellum and the
lobus opticus, to the posterior of the latter of which it then forms a
loop ventrally. Lying close to the optic foramen it passes through a
fine opening into the eye cavity and supplies the superior oblique
muscle of the eye. During its course it passes dorsally over the optic
nerve, and then crosses dorsally over the ophthalmic division of the
fifth pair of cranial nerves and the internal rectus muscle.

=The Trifacialis.=—(Fig. 62, No. _C_, 12). This, the fifth cranial, is a
mixed nerve and is divided into two parts, portio major and portio
minor.

The _portio major_ originates in the ganglion cells of the posterior
part of the brain. Commencing near the medulla oblongata it passes
through the posterior part of the brain, then upward and outward; and
along its route it forms the Gasserian ganglion, which lies partly in
the cranial cavity or in its wall.

The _portio minor_ consists of the downward passing fibers containing
the motoric elements which are distributed to the muscles of the jaw and
of the eye. The roots are found in the ganglion from the center and back
brain, close below the pathetic nerve origin, where the pathetic passes
between the lobus opticus and the pars peduncularis; it then takes a
lateral course between the two.

The fibers of the portio minor do not take part in the formation of the
Gasserian ganglion, but are only partly surrounded by it.

There are three nerve trunks given off of the trifacialis: the
ophthalmic, the superior maxillary, and the inferior maxillary.

The _ophthalmic division_ of the fifth nerve is the smallest of the
three branches. It emerges directly from the Gasserian ganglion, and
passes through a narrow bony canal in the base of the brain, below the
pathetic and the abducens, and through the foramen ophthalmicum. It then
enters the eye cavity above the optic nerve, and on the wall of the
cavity extends downward, and with regard to the eyeball, dorsally lying
close to the rectus internus muscle and close to the surface of the
eyeball. It passes along the olfactory nerve, extends under the superior
oblique muscle, and finally reaches the inner angle, or canthus, of the
eye. It here divides into the recurrent externa and the ethmoidalis. The
ethmoidalis branch is a straight continuation of the ophthalmic. It
extends along close to its fellow of the opposite side, and, over the
vomer, splits into two branches. The smaller of these branches breaks
through the bone cells of the jaw, continues upon its ventral surface in
a furrow extending forward, and terminates in the gum region. It
supplies the gum and point of the beak. The larger branch enters into
the cell substance extending to the tip of the beak, in its course
sending out a number of fine filaments, which spread out along the outer
surface. At this point these two branches may fuse. The larger branch is
endowed with the sense of touch.

The recurrent externa divides shortly after leaving the main trunk of
the eye cavity passes over the lacrimal gland. It gives two branches to
this gland and one to the membrana nictitans, and innervates the upper
eyelid. It then emerges from the eye cavity, passing over the os
lacrimale, and gives one or more branches to the integument of this
region, including the comb. This branch is large in birds with a large
comb. Branches pass in front of the lacrimal bone through the outer
nasal cavity and into its deeper structure.

Shortly after the ophthalmic branch has entered into the eye cavity and
before it crosses the optic nerve, it gives a fine branch to the motor
occuli.

The second and the third branches of the fifth cranial nerve are mixed.
They contain elements of both the portio major and the portio minor.
These two branches come from the lower part of the outer region of the
ganglion, and pass together through a cavity which is located between
the os petrosum and alæ and basis sphenoid, and then branch.

The ramus secundus, or _superior maxillary division_, of the trifacial,
is the second branch and passes into the orbit below the optic nerve and
the eyeball. It is called the recurrent infra-orbitale. It gives an
ascending branch to the gland of Harder, one to the conjunctiva, one to
the membrana nictitans, and one to the eyelids. It also gives a branch
to the skin below the eye and to the angle of the mouth. This latter
branch is called the _recurrent subcutaneous_. These two branches
communicate with the recurrent nasal ciliaris of the first trigeminus
branch. The second branch passes below the nasal opening, then passes on
and forms the alveolar nerve on the side between the gums. It sends
several recurrent posterior branches to the elevations on the back part
of the mouth. It extends forward to the point of the beak.

The _inferior maxillary division_ of the fifth is larger than the other
two. It is directed downward and outward then upward to the temporal
region. At the temporal region it divides into five parts. It gives a
branch to the temporalis muscle, one to the pterygoid muscle, and one to
the mylo-hyoideus. The main branch gives twigs to the parotid gland
region and enters into the dental canal of the lower jaw. Numerous
filaments break through the lower jaw bone, and then spread out on the
skin and rim of that bone. The largest branch, called the recurrent
maxillaris externa, comes out near the coronoid process. The rest of the
trunk extends to, and comes out of, several foramina at the anterior
point of the jaw bone.

These filaments are contained in grooves or cavities of the lower jaw
and terminate in touch buds.

The trifacialis fuses with the other cranial nerves and with the
sympathetic nervous system. Some of these fusions are as follows: The
recurrent ophthalmica fuses with the orbito-nasalis ganglion. Indirect
fusion of the recurrent maxillary division of this nerve takes place
near the Gasserian ganglion through the sympathetic nerves, the
temporo-lacrimalis, the facial nerves, the large cervical ganglion, and
indirectly with the glosso-pharyngeal and the vagus. This fusion has
been called the superior recurrent branch of the trigeminus, or
trifacialis.

There is a direct fusion of the superior recurrent maxillary division of
the fifth just before entering the upper jaw. This fusion is with the
spheno-palatine ganglion and the sympathetic carotidis cephalica, and
also with the large cervical ganglion.

=The Abducens= (Fig. 62, No. _C_, 13).—This nerve originates in the
somatic and motoric column along with the other nerves of the eye
muscles. Its nucleus lies in the circle of the pars commissuralis of the
cerebellum. The nerve then passes ventrally, as does the motoris oculi
and leaves the brain along the median line. This is a comparatively
large nerve and passes somewhat laterally and ventrally from the foramen
opticum through a canal in the sphenoid. It then enters the orbital
cavity. Some muscular twigs are given off to the quadratus and to the
pyramidalis muscle. This nerve also innervates the external rectus
muscle of the eye. The abducens anastomoses with the ramus ciliaris and
the ophthalmic nerve and gives fine nerve twigs to the ramus ciliaris
externus of the ciliary ganglion.

=The Facialis and the Acusticus.=—The facial nerve originates with the
auditory (Fig. 62, No. _C_, 14 and 15) in a very vaguely known manner,
from the cerebellum. It divides into three parts.

The first of these probably comes from the complex ganglion with the
posterior roots of the auditory. This part belongs to the somatic
sensory group of nerves. From this same group originates the auditory,
which spreads out into the cochlea and takes the impressions of sound.
This nerve is short and thick, and, at the point where it loses its
medullary covering on entering the cochlea, there is developed a
ganglion. This ganglion is similar to the spinal ganglia.

The second part is provided with one root which originates mesially and
ventrally, from the deeper ganglion cells. Some of the fibers from this
root constitute the vestibular branches. They accompany the auditory and
supply the anterior part of the ear labyrinth and the semicircular
canals. The larger part of the fibers of this trunk make up the
intermediate part of the facial. The geniculate ganglion is formed at
their fusion. The sympathetic spheno-palatine nerve emerges from this
ganglion, coming out of the aqueduct of Fallopius.

The third part, called the portio dura, is the main facialis. It is
located opposite the auditoria intermedia. Its roots may be traced to
the complex ganglion, from which they take a direction ventrally from
the median portion.

The facialis, after emerging from the aqueduct of Fallopius, takes a
curved course and partly fuses with the sympathetic temporo-lacrimalis
on the upper posterior wall of the ear drum. It is here accompanied by
the carotid and the cephalic arteries. It leaves the ear drum through an
opening in the quadrate bone, giving off a large branch to the
digastricus muscle and a small one to the stapedius of the columella
auris. The facialis trunk is quite large. It then passes downward along
the quadrate bone, where it receives a large branch from the
glosso-pharyngeus. This nerve also gives branches to the mylo-hyoideus
and the stylo-hyoideus muscle, crosses laterally the glosso-pharyngeus,
and finally fuses with branches of the subcutaneous and with the first,
the second, the third, and the fourth cervical nerves. After this fusion
the nerves innervate the skin of the anterior of the neck and the
constrictor colli muscle.

The facialis anastomoses as follows: with a fine branch of the
sympathetic temporo-lacrimalis, indirectly with the ramus trigeminus,
with the large cervical nerve ganglion and with the spheno-palatine
ganglion and nerve.

=The Vagus Group.=—The ninth, the tenth, and the eleventh cranial nerves
are by some anatomists called the vagus group, first so called by
Willis. They are made up of both sensory and motor nerves.

=The Glosso-pharyngeus.=—The roots of the glosso-pharyngeus (Fig. 62,
No. _C_, 16; Fig. 76, No. 13) emerge, along with those of the vagus,
from the medulla oblongata, and enter, as a short trunk, the foramen
jugulare et caroticum. Between these two nerves there is usually found a
thin portion of bone. The trunk of the glosso-pharyngeus forms a
ganglion in the foramen jugulare et caroticum where it receives
connecting branches from the near-by ganglion radicis and vagus nerve.
The glosso-pharyngeus passes out of the foramen jugulare et caroticum
above the large superior sympathetic nerve ganglion, with which it
communicates. The glosso-pharyngeus passes diagonally over the ramus
temporo-lacrimalis of the sympathetic system, and then receives a very
strong branch from the vagus (Fig. 76, No. 12). It sends a short branch
to the recurrent lacrimalis of the sympathetic system. At this point
there is formed a reddish-yellow ganglion, the petrosal ganglion, which
is similar to the petrosal ganglion of mammals. Frequently it is found
close below the large superior cervical nerve ganglion. The petrosal
ganglion is frequently connected by special fibers with the cervical
nerve ganglion, the large superior cervical nerve ganglion and the
ganglion radicis vagi. The glosso-pharyngeus is divided into the
following branches.

First, the recurrent pharyngeus which gives branches to the upper part
of the throat and which is tortuous in its course. It receives a branch
from the superior cervical nerve ganglion and gives off branches to the
salivary glands and papillæ of the posterior tongue region.

Second, the recurrent lingualis, which passes with the lingual artery
over the hyoid bone to the base of the tongue and to the papillæ.
Another branch passes below the tongue bone and supplies the tongue and
the pharynx. The glosso-pharyngeal is a mixed nerve.

[Illustration:

  FIG. 76.—Photograph of spinal cord of a hen. 1, Cerebrum. 2, The
    olfactory nerve terminating at 3, the turbinated bones. 4, The
    superior maxillary division of the fifth nerve dividing. 5, The eye
    with the upper part laid open. 6, The cervical segment. 7, The
    lumbo-sacral segment. 8, The lungs. 9, The kidneys lying above the
    peritoneum. 10, The terminal filament of the spinal cord. 11, The
    hypoglossal nerve. 12, The vagus nerve. 13, The glosso-pharyngeal
    nerve. 14, The branch from the vagus.
]

=The Vagus.=—The vagus, or pneumogastricus (Fig. 18, No. 5; Fig. 62, No.
_C_, 17; Fig. 76, No. 12), a mixed nerve, forms a ganglion in the
foramen through which it passes. The foramen lies between the os
petrosum and os occipitale, close to the foramen jugulare, above and to
the inside of it.

The ganglionic root of the vagus communicates with the superior cervical
nerve ganglion. The vagus, after coming out of the foramen, takes up
branches of the spinal accessory, passes to the superior nerve ganglion,
crosses the carotid artery, and then, accompanied by the internal
jugular, it connects by a branch with the hypoglossal. It then
communicates with the petrosal ganglion, and receives a long branch from
the superior cervical ganglion. It then extends along the neck with the
jugular vein and often fuses with the sympathetic ganglionic plexuses.
As it passes, it is interwoven with the glosso-pharyngeus, but each
nerve element retains its own individuality. Extending down the neck, on
entering the thoracic cavity, it lies between the plexus brachialis and
the carotid artery. Then it passes below the subclavian artery, and
between the bronchial tubes, the aorta pulmonalis, and the subclavian
vein. Then ventrally it rests upon the glands, and the right and the
left vagi fuse or unite. From here they radiate down to the stomach in
fan-shape, and, continuing, they fuse with the sympathetic system.

The other branches of the vagus are:

The first branch is the recurrent laryngeus, which supplies the lower
end of the bronchial tubes, and the esophagus, then enters above the
bronchus near the origin of the subclavian artery as the recurrent
cardiacus.

The second are the recurrent pulmonale which pass into the lungs, each
fusing with its fellow from the opposite side, and giving off branches
inferior to the vena cava including a branch to the heart.

The third are the recurrent hepatici which pass through the diaphragm
and are distributed to the liver.

=The Accessorius Spinalis.=—This is a very small motor nerve (Fig. 62,
No. _C_, 18). It comes out between the dorsal and the ventral root of
the third cervical nerve. It lies close to the neck and extends
anteriorly, receiving roots from the first and the second cervical
nerve. It passes through the occipital foramen into the brain cavity and
then enters the ganglion radicis vagi. It passes out of the cranial
cavity through the foramen jugulare. It then partly fuses with the vagus
and partly, as a fine branch, with the subcutaneous colli.

=The Hypoglossus.=—The hypoglossus is a motor nerve (Fig. 62, No. _C_,
19). It originates anterior to the eleventh pair of cranial nerves, and
from the same ganglion as the abducens and the motor oculi. It leaves
the medulla oblongata from its ventral surface, and passes with a
posterior and an anterior branch out of the cranial cavity through two
separate foramina in the os occipitale laterale. The posterior branch,
much smaller than the anterior, passes between the cranial bones and the
cervical sympathetic nerve; it then passes at right angles through the
rectus capitis anticus, and, while closely following the carotid artery,
it fuses with the anterior branch. The larger, anterior branch, much
stronger than the posterior, sends a short strong branch to the
complexus muscle. The rest of this branch, which probably has
sympathetic elements, is disposed as is a spinal nerve. It crosses the
sympathetic nerve, and at this point forms a typical cervical
sympathetic ganglion. It also forms a short loop with the recurrent
ventralis of the first cervical plexus. From this loop, after it has
given off several branches to the muscles of the neck, it gives off one
or two strong branches, which fuse with each other and with the
posterior thin branch, thus forming the trunk of the hypoglossus. It
receives many elements from the first cervical nerves.

The hypoglossus sometimes communicates with the vagus, crosses over the
latter, and divides itself into two main branches, as follows:

First, the _recurrent laryngo-lingualis_, which passes between the
cornua of the os hyoideum and the larynx to the anterior part, and
furnishes the principal tongue muscles. It extends along the inferior
surface of the tongue and fuses with the one of the other side and
extends to the free tip of the tongue. This nerve probably receives
sensory elements from the second root and from the confluent of the
first cervical nerve. This form of anastomosis is well marked in birds
with thick tongues, as ducks.

Second, the _recurrent laryngeus_ furnishes the muscles of the superior
larynx and of the tongue skeleton. It extends downward and also
furnishes the muscles of the trachea. It follows the course of the
jugular vein and at the entrance of the chest supplies the furcula. The
nerve passes into the thorax, downward along the side of the bronchial
tubes, and supplies innervation to all the muscles of the inferior
larynx.


                            THE SPINAL CORD

=Structure of the Cord.=—The spinal cord is called the myelon or medulla
spinalis. It is a comparatively large, white, irregularly cylindrical
cord, flattened from above downward. It extends from the foramen magnum
at the base of the medulla to the caudal portion of the spinal canal
where it terminates in a fine filament. In order to allow considerable
motion of the spinal column without danger of injury to the spinal cord,
the cord is loosely suspended in the canal. The meninges, or coverings,
are continued from the brain. In addition to these there are to be found
arteries, veins, and nerves entering and others making their exit from
the canal and from the cord. At the cervico-dorsal juncture, where the
brachial plexus is given off, the cord is enlarged. There is another
enlargement at the point where the lumbo-sacral plexus is given off. At
this point, superiorly, there is a longitudinal cavity called the _sinus
rhomboidalis_. This sinus contains a gelatinous substance. There is a
pair of nerves given off at each intervertebral foramen. Thus there are
as many pairs of spinal nerves as there are vertebral segments. The
inferior root is the motor root and carries the impulses from the cord
to the periphery. The superior root is the sensory branch and carries
the impulses from the periphery to the cord, and thence the impulse is
carried to the centers in the brain. The sensory and the motor roots are
of about equal size. The inferior have more numerous filaments. The
ganglion on the superior or sensory root is relatively large. In the
sacral region the sensory and the motor branches pass through their own
bony canal.

White _rami communicantes_ are given off at each intervertebral foramen
to the sympathetic system and gray rami are received from the
sympathetic ganglia. Thus there is established a direct communication
between the sympathetic and the spinal system. There is a ganglion on
the superior root just outside the spinal cord.

The ganglionic portion, or _gray matter_, is arranged in the center of
the cord in two comma-shaped parts forming an X. The white matter, or
the material forming the fibers, is arranged around the central
ganglionic portion.

The spinal cord may be divided into two lateral symmetrical halves.
There are two longitudinal fissures, one on the upper and the other on
the lower half. The upper called the _superior median fissure_ is narrow
but deep. The one on the inferior side, called the _inferior median_, is
usually more pronounced. The superior parts of the gray matter are
called the superior cornua, or horns; the inferior parts the inferior
cornua, or horns. The center of the cord is pierced by a _central canal_
which communicates with the fourth ventricle at the calamus scriptorius.


               STRUCTURE OF THE NERVE TRUNKS AND GANGLIA

The protoplasmic processes called _dendrites_ have a similar structure
to the cell body. The dendrites branch dichotomously, become rapidly
smaller, and usually end at no great distance from the cell body.

The _axone_ or _axis cylinder process_, differs from the cell body and
from the dendrites. It does not contain chromophilic granules. It
consists entirely of neurofibrils and perifibrillar substance. It
emerges from the cell at an enlargement known as the axone hill. This
hill is free from chromophilic bodies.

Nerves are divided into two kinds, medullated and non-medullated.

_Medullated nerves_ are divided into two kinds: medullated nerves with a
neurolemma, and medullated nerves without a neurolemma.

Medullated nerves with a neurolemma consists of an axone, a medullary
sheath, and a neurolemma. A delicate membrane called an axolemma, or
periaxial sheath envelops the axone. The medullary sheath called myelin,
is semifluid, somewhat resembling fat. The outer covering is the
neurolemma, or sheath of Schwann. It is a delicate, structureless
membrane which incloses the myelin. There is under this sheath an
occasional oval nucleus. At intervals there are constrictions, or nodes,
called the constrictions of Ranvier. The part between the nodes is
called the internode.

The medullated axones without a neurolemma are the medullated nerve
fibers of the central nervous system.

The non-medullated axones, or _non-medullated nerve fibers_, are divided
into non-medullated axones with and those without, a neurolemma.

The non-medullated axone without a neurolemma is merely a naked axone.
They are confined to the gray matter and to the beginnings and endings
of sheath axones, all the latter being uncovered for a short distance
after leaving the nerve cell body and also just before reaching their
terminations.

The long axones serve to make connections with the peripheral, or
distant, nerve cell, muscle cell, or gland cell; while the shorter
axones of certain neurones divide into terminal branches in the
immediate vicinity of its cell body, presumably to come into relation
with other nerve cells in the same or adjacent groups.

[Illustration:

  FIG. 77.—Histological structure of tissues.

  1. Non-striated or involuntary muscle cell. _a._ 1, Nucleus; 2,
    Protoplasm. _b._ Transverse section showing nuclei in the center of
    the cells that are cut through the nuclear zone. _c._ A
    cross-section of the connective tissue which binds together the
    muscle cells. _d._ A section showing the so-called intercellular
    bridges.

  2. A cross-section of the rectus abdominalis. 1, The endomysium which
    binds the cells into primary fasciculi or bundles. 2, The perimysium
    which surround the bundles of fasciculi. 3, The epimysium which
    surrounds the muscle. These binding structures are white fibrous
    connective tissue.

  3. A longitudinal section at the juncture of a muscle and tendon. _a_,
    The juncture between the muscle and tendon. Note the many nuclei in
    both muscle and tendon. This is voluntary or striated muscle which
    make up the dermal, dermo-osseous and skeletal muscles.

  4. A longitudinal section of heart muscle. _a_, Connective-tissue
    cell. _b_, Nucleus of a muscle cell. _c_, Cement line between the
    muscle discs. _d_, The cell or segment.

  5. A bipolar ganglionic nerve cell. _a_, The nucleus. _b_, The
    nucleolus. _c_, The fibrillar structure. _d_, The medullary sheath.

  6. A diagram showing the scheme of the peripheral nerve trunk. _a_,
    The neuraxis of the peripheral sensory neurone. _b_, The spinal
    ganglion of the superior or sensory root. _c_, The dendrite or
    peripheral nerve fiber of the sensory nerve. _d_, The nerve trunk.
    _f_, The sympathetic nerve ganglion connected with the spinal cord
    through the white and the gray ramus communicans. _e_, The neuraxis
    of the sympathetic neurone. _g_, Neuraxis or trunk of the motor
    neurone or nerve cell. _h_, The anterior horn of the gray matter of
    the spinal cord.

  7. A diagram of a peripheral sensory neurone. _a_, The neuraxis which
    ends in the spinal cord or brain. _b_, The T-shaped division of
    Ranvier. _c_, The dendrite or sensory nerve fiber in the nerve
    trunk. _d_, The nucleus and nucleolus of the cell _e._, _f._ the
    axis cylinder process of the cell. _g_, The telodendrions or
    terminal branches of the dendrite or axis cylinder.

  8. A schematic diagram of the sensory motor reflex. _a_, The
    telodendria. _b_, The dendrite. _c_, Nerve cell of the motor
    neurone. _d_, The motor neurone. _f_, The muscle fiber. _g_, The
    neuraxis of both sensory and motor neurones, the upper being the
    sensory. _h_, The nerve cell in the sensory ganglion. _i_, The
    sensory neurone or axis cylinder (nerve fiber). _j_, The skin with
    peripheral telodendrion of sensory neurone.
]

_Neurones_ are devoted to the maintenance of functions. Reproductive
neurones are so arranged as to receive afferent nerve impulses from
other tissues; emissive neurones give off efferent nerve impulses. The
former are sensory neurones; the latter are motor neurones if connected
with muscles, and excito-glandular if connected with gland cells. The
basis, then, of the nerve system is a series of neurones, with
projecting and association processes, coördinated for the purpose of
performing specific actions manifested either by motion, by trophic
changes, or by the apperception of stimuli of a chemic, mechanic
(tactile and auditory), thermal, or photic nature.

The whole of the nerve structure is composed of the nerve tissue and
supporting connective tissue. The neurones constitute the nerve tissue,
while the supportive tissue is composed of neuroglia and of white
fibrous tissue derived either from the investing membrane or from the
sheaths of its numerous vascular channels.

The neurones, or nerve cells, exhibit marked variations as to external
characters, dimensions, and form. The neurone presents a swollen cell
mass and a nucleus; it is known as the ganglion cell. From this cell
body are given off a number of processes of two distinct kinds: first,
protoplasmic processes, which are commonly branched, called dendrites;
second, a single, thinner, and paler process; the axis cylinder process.

The bodies of cells vary in size from 4 to 100 microns or more in
diameter. The largest cells occur in the inferior horn of the spinal
cord, in the spinal ganglia, in the large pyramidal cell layer of the
cerebral cortex, in the Purkinjean cell layer of the cerebellum, and in
Clark’s column of the spinal cord. Very small cells occur in the
olfactory bulbs, in the granular layer of the cerebral and cerebellar
cortex, and in the gliosum cornuale of the cord.

Nerve cells are classified according to the number of processes arising
from the cell body, and neurones are referred to as unipolar, bipolar,
and multipolar.

_Unipolar cells_ are met with frequently in early stages of embryonic
development, but are rare in adults, occurring only in the retina, in
the olfactory bulb, and within the baskets of the Purkinjean cells of
the cerebellum. The cells of the cerebro-spinal ganglia, except the
cochlear and vestibular, are apparently unipolar, but they are
developmentally and functionally of bipolar nature.

_Bipolar cells_ are found almost exclusively in the peripheral sensory
system, as in the olfactory membrane, in the retina, in the cochlear and
vestibular ganglia, and in the cerebro-spinal ganglia of the embryo.

_Multipolar cells_ are the most numerous and form the principal elements
of nerve centers throughout the system. They are termed multipolar
because of the greater or lesser number of dendrites given off in
addition to the single axone.

The body of the nerve cell consists of a mass of protoplasm surrounding
a nucleus. The cytoplasm of the nerve cell consists of two distinct
substances: first, neurofibrils; second, perifibrillar substance. In
most nerve cells there is a third substance called chromophilic bodies.

The _neurofibrils_, extremely delicate, are continuous throughout the
cell body and all of its processes. Within the body of the cell they
cross and interlace and probably anastomose.

The _perifibrillar substance_ is a fluid or a semifluid substance which
both in the cell body and in the processes surrounds and separates the
neurofibrils.

The _chromophilic bodies_ are granules or groups of granules which occur
in the cytoplasm of all the larger and of many of the smaller nerve
cells.


                           THE SPINAL NERVES

The first pair of spinal nerves come out between the atlas and the
occipital bone. Each nerve divides into three branches. The first is the
_anterior branch_ which innervates the dorsalis, the biventer cervicis,
the cervicales, and the caput posticus muscles. The second is the
_recurrent ventralis_ which passes mesially and downward from the
recurrent communicans. It innervates the rectus capitis anticus muscle
and joins a branch of the hypoglossal nerve. There is given off a white
ramus communicans to the sympathetic nerve.

The second spinal nerve emerges from the opening between the first and
the second cervical vertebræ and is similarly disposed as the first
cervical. It gives off a branch called the recurrent ventralis which
fuses with branches of the first cervical and the hypoglossal nerve.
This nerve innervates the complexus muscle.

The succeeding cervical nerves emerge in a similar manner down the neck
and are distributed to the muscles and other structures of the cervical
region. The second, the third, and the fourth cervical nerve gives off
branches which form anastomosing loops with the facial nerve.

According to Gadow the last cervical nerve passes between the last
cervical and the first dorsal segment. There are thus fifteen pair of
cervical nerves.

The first pair of _dorsal nerves_ pass out between the first two dorsal
vertebræ. The first few dorsal nerve branches innervate only the trunk
muscles. Other branches supply the skin and the other adjacent
integument. The ventral branches of the cervical nerves often
communicate with the ventral branches of the first dorsal nerves. These
branches are larger than the superior branches and aid in the formation
of the brachial plexus. Smaller inferior branches are distributed to the
scalenus and other muscles, and extend as far posterior as the
intestines.

The dorsal branches of the spinal nerves in the lumbo-sacral region are
very small, on account of the lack of extensive development of the
muscles of this region. The elements entering into these nerve trunks
are largely vasomotor nerves. In addition to the upper twigs supplying
the skin and the other integument of the region, other branches descend
into the abdominal cavity.

The caudal spinal nerves are not well developed and disappear in the
region of the caudal vertebræ. The dorsal branches innervate the levator
muscles, and the ventral branches the depressor muscles.

There is thus given off, throughout the vertebral column, a pair of
nerves between each two vertebral segments, making as many pairs of
nerves for the region as there are vertebral segments of that region.

=The Brachial Plexus.=—The brachial plexus (Fig. 73, No. 19) arises
principally from the roots of the last three cervical and the first
dorsal spinal nerves. These branches anastomose beneath the deep face of
the scapulo-humeral articulation.

The brachial plexus divides into two distinct parts. The first (Fig. 73,
No. 20) the dorsal called the superior thoracic is distributed to the
serratus and the rhomboideus muscle. The second is the inferior thoracic
(Fig. 73, No. 21), which consists of the main plexus, and which gives
off muscular branches especially to the sterno-coracoideus and to the
main portion passing on as the nerve trunk to the structures of the
wing.

From the superior thoracic plexus there are several secondary plexuses
formed.

The _dorsalis_ or _serratus plexus_. This plexus is located adjacent to
the anterior part of the main plexus and is formed of from two to four
spinal nerve branches. The rhomboideus is supplied by branches which may
be traced to the first root of this plexus. This nerve is called the
rhomboideus superficialis. Another nerve is given off from the middle
part of the dorsal side of the plexus and is called the rhomboideus
profundus. A third, the superficialis serratus, is the largest of the
branches. It breaks up into terminal branches, one going to each
serration, or digitation, of the serratus muscle. Branches from the
anterior portion of this plexus are distributed to the patagii muscles.

The superior brachial plexus gives off the following nerves:

The _subcoraco-scapularis_, which is purely a motor nerve, springs from
the anterior roots of the plexus. It gives off a branch to the following
three muscles: subcoracoideus, subcoracoido-scapularis, and
scapulo-humeralis.

The _scapulo-humeralis_ is distributed to the scapular humeral region.

The _latissimus dorsi_ is located on the peripheral border of the
scapulo-humeralis or supraspinatus. It originates from the second, and
the fourth nerve roots of the plexus. It is located on the dorsal side
of the plexus. It divides into two main branches, one going to the
latissimus dorsi and the other to the scapulo-humeralis muscle. From the
side are given off branches which supply the patagii muscle and enter
into the formation of the dorso-cutaneous plexus.

The _axillaris_ springs from the second and the third root of the
brachial plexus, extends in a lateral direction, passing the ventral and
distal rim of the insertional part of the posterior scapulo-humeralis or
teres et infraspinatus and enters near the capsular ligament of the
shoulder-joint. It gives off to this joint a small branch, called the
recurrent articularis, which passes outward between the triceps
brachialis and the humerus. It lies on the inner side of the major
deltoid, and patagii muscles, and also the skin of the lateral shoulder
and the upper arm region. The recurrent axillaris communicates with the
main branch of the radial nerve.

The _cutaneus brachii superior_ is a small nerve which springs from the
last brachial plexus root and passes between the skin and the triceps
brachii muscle on the dorsal surface of the upper arm, or brachial,
region. It extends down over the elbow region, where it gives off
numerous branches to the skin of these regions, to the meta-patagium and
to the extensor muscles of the upper arm.

The _brachialis longus superior_ is a large nerve trunk which springs
from most of the other plexus roots. It extends around to the dorsal
side of the upper arm and supplies the skin, the feathers, and the
muscles of the forearm and the hand. Branches from this nerve trunk
supply the triceps brachii and other muscles of the region. The main
branch passes between the radius and the ulna, and, passing the
elbow-joint, gives off branches to that joint. Passing on, it divides
into two branches. One of these extends superficially over the upper
part of the condylus ulnaris and supplies the extensor digitorum
communis and the extensor metacarpi ulnaris, or flexor metacarpi
radialis muscles, and, continuing superficially to the ulnar side, is
distributed to the skin of the region. The second, a deep branch,
extends on the ulnar side of the radius over the extensor indicis
longus, and innervates the latter muscle, the extensor pollicis longus,
the extensor pollicis brevis, the adductor pollicis, the interosseous
palmaris, and the flexor digitorum.

The inferior brachial plexus gives off the following branches:

The _supra-coracoideus_, a large nerve which springs from the first main
root of the plexus, and passes outward through the foramen coracoideum
of the sternal ligament.

The _sterno-coracoideus_, a small nerve which extends downward from the
plexus.

The somewhat large _posterior coraco-brachialis_, nerve which springs
from one or two middle roots of the plexus and accompanies the pectoral
nerve.

The _anterior thoracic_, a large nerve which springs from two or three
of the posterior roots of the plexus and extends to the shoulder cavity
where it branches. The anterior branch is distributed to the patagium
and the front part of the pectoral muscles. The posterior branch
supplies muscles along the side of the thorax and extends into the
abdominal muscles.

The _anterior coraco-brachialis_, a small nerve which springs mostly
from the inferior longus brachialis, passes to the distal end of the
tuberculum humeralis radii, then passes backward between the front part
of the humerus and the biceps, where it supplies the anterior
coraco-brachialis.

The _cutaneous brachialis_ et _inferior brachialis_, a small nerve which
springs from the posterior roots of the plexus. It is distributed to the
skin of the region and branches are given off to the patagii and the
ventral wing surface. A few branches extend as far as the upper arm.

The _brachialis longus inferior_ (Fig. 68, No. 2), a continuation of the
main trunk of the inferior brachial nerve, which comes out of all the
plexus roots except the first. It gives off some branches to the
pectoral region and then enters the shoulder cavity. It gives off the
anterior coraco-brachialis, passes down the humerus in an S-shape, and
divides into two branches, the ulnar and the median.

The _ulnar nerve_ (Fig. 67, No. 3) divides into numerous branches which
are distributed to the ulnar side of the forearm and the hand. The ulnar
nerve passes below the skin of the ulnar outside rim of the forearm and
gives branches to the carpi ulnaris, finally supplying the flexor
digitorum; it then passes with the tendon of this muscle downward to the
interosseous dorsalis, the abductor indicis, or flexor minimi brevis,
the flexor pollicis, and the abductor pollicis, or extensor proprius
pollicis.

The _median nerve_ (Fig. 67, No. 2) extends down the arm and gives
branches to the biceps muscle, and to the patagii region. Continuing,
the median nerve supplies the pronator muscle and the brachialis
inferior, or brachialis anticus, and then divides into two branches. The
first and largest branch passes between the two pronator muscles giving
branches to the pronator profundus, or pronator longus, and the flexor
digitorum profundus muscle. This nerve then passes anteriorly along the
tendon to the base of the digit, and, on the dorsal side, joins the
other branch of the median nerve. At this point there is often a plexus,
and at the point of fusion of the ulnar nerve on the ulnar side there
may also be a small plexus. These plexuses mainly supply the skin of
these regions. The second branch, passes forward, crosses the extensor
carpi radialis and lies just below the pronator profundus, or pronator
longus, giving branches to the skin. It passes downward on the radial
side of the ulnar and supplies the muscles of that part; it then
continues down the hand. Branches are given off to the extensor proprius
pollicis, the interosseous dorsalis, the flexor digitorum, and to the
skin between the thumb and the forefinger.

The _intercostal nerves_ (Fig. 70, No. 18) are given off from the spinal
cord of the dorsal region. The superior branches are small and supply
the superior dorsal region. The inferior branches lie one behind each
rib, innervate the intercostal muscles, and give a few twigs to the
superficial thoracic muscles.

=The Lumbo-sacral, or Crural, Nerve Plexus.=—The crural plexus (Fig. 70,
No. 35 and 36) is made up of trunks from the last two lumbar and first
four sacral spinal nerves. There are two portions of this plexus
separated by a considerable distance.

The anterior portion (Fig. 70, No. 35) consists of the lumbar nerves and
a portion of the first sacral nerves. The fusion takes place on the bony
ridge that separates the lumbar from the sacral region.

The posterior portion (Fig. 70, No. 36) consists of a part of the first
sacral and all of the three succeeding nerves.

The anterior nerve of this plexus is distributed to the abdominal
muscles. An anterior branch is given off to the sartorius. A large
cutaneous branch enters between the sartorius and the ilio-trochanteric
eminence, and supplies the outer and the upper surface of the upper
thigh region. Several short branches are given off from the middle, or
main, mass of the crural plexus to the ilio-trochanteric, or gluteal,
muscle. Another nerve passes over the side of the sartorius adjacent to
the femoro-tibialis, or extensor femoris, and supplies the
ilio-tibialis, or gluteus primus. The rest of this section of the crural
nerves pass in a distal direction over the inner and front side of the
cutaneous nerve and enter the ilio-femoralis, or gluteus medius, the
ambiens and the femoro-tibialis muscle.

The _furcalis nerve_ comes out between the last two lumbo-sacral
vertebræ.

The _obturator nerve_ springs from several roots. The anterior root of
this nerve comes from the main trunk of the crural plexus, and its last
root from the furcalis nerve. The obturator nerve extends in a ventral
direction from the plexus, then horizontally on the inner surface of the
abdominal cavity. It gives off twigs to the obturator muscle and then
passes through the obturator foramen. After leaving the abdominal cavity
it gives branches to the accessorius, the obturator, and, the
pubio-femoral, or adductor longus muscle.

The crural plexus gives off another large nerve trunk which extends
downward. Shortly after emerging from the plexus it gives off a muscular
branch to the ilio-femoralis, or gluteus medius muscle. It then passes
between this muscle and the shaft of the femur, to the inner posterior
surface of the thigh, and to the inner surface of the knee. It gives off
a branch to the structures of the knee. At the knee this nerve
terminates in several branches, some of which pass to the inner surface
of the tibial head, the internal lateral ligament, the periosteum, the
internal condyle, and finally to the upper part of the head of the
gastrocnemius muscle.

The main part of this nerve passes downward as the cutaneous nerve,
along the inner surface of the lower thigh.

The _ischiadic plexus_ (Fig. 64, No. 41) has five to six roots, which
fuse into the ischiadic trunk. This main trunk extends out of the
abdominal cavity, through the ischiadic foramen, close behind the
anterior trochanter of the ilium (Fig. 65, No. 1). It gives a branch to
the external ilio-femoral or gluteus medius, and a branch to the
post-acetabular portion of the ilio-tibialis, or gluteus primus muscle.
The main trunk (Fig. 69, No. 13) passes downward to the lower portion of
the thigh. In this course there are two branches which run parallel to
the femoral artery and the femoral vein. It gives off a small muscular
branch to the accessorius, and further down gives off a long slender
branch to the outside of the knee-joint. It gives off a lateral
cutaneous branch (Fig. 66, No. 7) to the posterior outer portion of the
lower thigh. It supplies motor fibers to the external head of the
gastrocnemius muscle.

At the knee region the ischiadica divides into three parts. The largest
branch (Fig. 69, No. 14) passes with the tendon of the ilio-fibularis,
or biceps femoris muscle, through a loop, the biceps band, and lies on
the upper lateral surface of the fibula. It is covered by the external
head of the gastrocnemius muscle. It innervates the three posterior
muscles of the lower thigh, and then divides into two branches. One, the
superficialis peroneus (Fig. 69, No. 16) passes with the profundus
nerve, forming a double trunk and occupying the tibio-fibular groove on
the antero-lateral side. It passes over the transverse ligament and the
tibio-metatarsal joint, and after sending small branches to the
structures of the tibial side of the metatarsus, it ends as a cutaneous
nerve on the upper side of the third and the fourth toe.

The other branch is the _peroneus profundus_, which separates from the
peroneus superficialis and passes downward in company with the tendons,
under the transverse ligament, and then along the anterior upper surface
of the metatarsus, where it innervates the muscles of that region. It
gives branches to the malleolus, to the tendons of the third toe, and to
the median part of the second toe, and supplies the cutaneous structures
of the third and the fourth toe.

The third branch of the _ischiadica_, a long nerve, is given off just
after the ischiadica passes through the loop. It passes downward between
the two peroneal nerves. It is covered by a sheath. It passes over the
posterior outside rim of the intertarsal joint and innervates the tendon
sheath. The main portion of this nerve is located on the anterior
surface of the tendon Achillis, and passes down on the plantar side, and
innervates the periosteum and all plantar foot muscles. It finally
radiates to the plantar surface of the three anterior toes.

The integument of the toes is sparingly supplied with nerves.

The nerve trunks that do not pass through the biceps band, or loop can
be divided into a medial (Fig. 69, No. 15) and a lateral (Fig. 69, No.
17) portion. The medial portion (Fig. 69, No. 15) soon divides into
numerous branches which supply the muscles of the posterior and the
inner portion of the thigh. A rather large, long branch passes downward
along the tendon of the plantar muscle, which lies on the posterior
median edge of the tibia, and gives off twigs to the median and
posterior part of the intertarsal joint, supplying the periosteum and
other structures and the adjacent skin. It passes downward along the
outer side of the medial metatarsal insertion of the tendon Achillis.

The _fifth branch_ is given off from the second trunk and lies
laterally. It is covered by the external head of the gastrocnemius,
passes along the vena saphena, and gives off a short main branch to the
inner side of the intertarsal joint. The main part passes the tibial
side of the joint, becomes subcutaneous, and finally innervates the two
plantar muscles. A lateral ascending inner branch innervates the flexor
perforatus digitorum, and, in company with an outer branch, the external
head of the gastrocnemius, and also the flexor pedis perforatus.

The _plexus pedundus_ is formed from the spinal nerves coming out of the
plexus ischiadicus. These fibers emerge caudalward and are directed
horizontally. They frequently anastomose with each other, especially on
the pubic rim and on the outside of the plexus ischiadicus. These
branches are deeply imbedded in the kidney substance and innervate the
pubio-coccygeus, or depressor coccygis lateralis, the ilio-coccygeus,
the transversalis, the sphincter, and other muscles of this region, and
the skin of the anal region.


                               THE BRAIN

=The Brain Coverings.=—The cerebro-spinal axis of birds is similar to
that of mammals. The _meninges of the brain_ are three in number, dura
mater, arachnoid, and pia mater. The _dura mater_ is the thickest. It is
constructed of white fibrous connective tissue, and lines the cranial
cavity. Thus it serves as an internal periosteum. It is continuous with
the spinal dura mater at the foramen magnum, and is also prolonged as a
sheath of the nerves. In birds of flight where the air-sacs and
reservoirs are developed to the highest state, Sappy finds that, “just
as the medullary tissue is replaced by air in the bones of birds, so
might it be imagined that the subarachnoid fluid is also replaced by air
around the spinal cord,” and observations justify the correctness of
this statement. The dura mater measures exactly the volume of the marrow
in birds; so that there does not exist between the fibers and the
nervous surface any space for an accumulation of liquid. This anatomical
fact is sufficient to demonstrate the absence of subarachnoid fluid in
the bird. In denying the existence of this fluid, it ought to be added
that in this class of vertebrates, the spinal prolongation is covered by
a triple envelope; and that between the pia mater and the dura mater is
a thin transparent membrane, which is lubricated by a serous fluid. This
fluid however does not collect; it only moistens the arachnoid membrane.

The _arachnoid_ is located between the dura mater above and the pia
mater below. The pia mater adheres closely to the nerve tissue.

The _falx cerebri_ exists in fowls and in turkeys. It has the form of a
segment of a circle, and extends from the middle of the interval of the
openings for the olfactory nerves to the tentorium cerebelli. The falx
cerebelli is absent. The tentorium is small and is sustained by a bony
plate, and there are in addition two folds, one on each side, that
separate the hemispheres from the tubercula quadrigemina. Owing to the
absence of the falx cerebelli, the meninges lie close together. The falx
cerebri is ossified in birds.

=The Brain Structure.=—The brain (Fig. 62, _C_ and Fig. 75, _A_ and _C_)
is made up of three principal parts: the cerebrum, the cerebellum and
the medulla oblongata. In a fowl of medium size the brain weighs about
150 grains.

The pons varolii is absent in birds. The crura cerebelli (Fig. 75, No.
9) are immediately connected with the corpora restiformia. The lower
face of the isthmus is convex posteriorly; in front, the tubercula
bigemina (Fig. 75, No. 4) are united to each other by a comparatively
large transverse cord, formed by the optic nerves intercrossing in the
median line. The superior face of the medulla oblongata is depressed
above to constitute a fourth ventricle; in front of this ventricle are
the tubercula bigemina, or _optic lobes_. These two voluminous tubercles
are separated from each other above, where they embrace the cerebellum,
and are salient on the sides of the lower face. They are hollow
internally, and communicate with the aqueduct of Sylvius. The thalami
optici are not well developed.

A large _transverse fissure_ divides the cerebrum from the cerebellum
(Fig. 75, No. 5). The optic chiasm (Fig. 75, No. 15) behind which lies
the hypophysis (Fig. 62, No. _C_, 20) covers the region of the middle
brain. The large transverse fissure is the dividing line between the
hemispheres and the optic lobes. If the hypophysis be removed there will
be observed a slit surrounded by gray matter which is called the tuber
cinereum et infundibulum (Fig. 75, No. 18). On the pars commissuralis
and the after brain there are visible the roots of the fifth, the ninth,
the tenth, and the twelfth pairs of cranial nerves. Close beside the
median furrow which extends to the front part of the long furrow of the
spinal cord there is observed the third pair of cranial nerves, which
have their origin in the middle brain. The fourth pair of cranial nerves
extend from the roof of the middle brain on both sides between the
middle brain and the optic lobes. These nerves finally emerge and become
visible on the ventral surface.

The sixth nerve is visible near the middle furrow and almost in the
middle of the pyramids, and near the roots of the fifth, the seventh,
the ninth, the tenth, and the twelfth pair of cranial nerves.


                       THE DIVISIONS OF THE BRAIN

                             (Thalamus
                             (Pineal body
                             (Infundibulum
                             (Hypophysis
                Forebrain    (Optic tract and chiasm
                             (Cerebral hemispheres
                             (Olfactory lobes
                             (Third ventricle
                             (Lateral ventricles

                             (Peduncles of the cerebrum
                Midbrain     (Optic lobes
                             (Aqueduct


                             (Medulla oblongata
                Hindbrain    (Cerebellum
                             (Fourth ventricle

The _medulla oblongata_ (Fig. 62, No. _C_, 1; Fig. 75, _A_ and _C_)
terminates anteriorly in the pars commissuralis and the pars
peduncularis. As the spinal cord approaches the head there is a gradual
swelling, or lateral thickening, which merges into the medulla
oblongata. The superior and the inferior surface of the medulla
oblongata (Fig. 75, No. _A_, 1 and _C_, 17) are flattened. There is a
shallow furrow and a slight swelling at the point where the hypoglossal
nerve emerges. The central canal of the spinal cord gradually comes
closer to the upper surface and communicates with the fourth ventricle,
at which point the posterior raphe is shortened and the sulcus
longitudinalis posterior becomes shallow. At the point where the central
canal terminates in the fourth ventricle there is a V-shaped point
called the _calamus scriptorius_ (Fig. 75, No. 2). The _fourth
ventricle_ is located on the upper wall of the medulla oblongata below
the cerebellum, and is bounded laterally by the peduncles of the
cerebellum. It is marked posteriorly by the calamus scriptorius and
anteriorly by the valve of _Vieussens_.

The _valve_ of _Vieussens_ is located at the posterior end of the
aqueduct of Sylvius. The posterior part of the fourth ventricle is
marked by grooves or furrows. Extending along the central part of the
floor of the fourth ventricle there is a sulcus, or groove, called the
sulcus centralis, which divides the superior pyramids. On the median
lateral sides there are two points of gray substance which form the alæ
cinereæ. The roots of the pneumogastric, the glosso-pharyngeal, and the
spinal accessory may be traced to the alæ cineræ and the gray matter of
the ridges of the medulla oblongata. The sixth pair of the cranial
nerves emerge from the medulla near the sulcus centralis and to the side
of the auditory nerve. Part of the trigeminus emerges from the rim of
the furrow next to the ridge. At the outer border of the medulla are
observed the thick ends of the roots of the pneumogastric, the spinal
accessory, the glosso-pharyngeal, and the auditory facialis.

On both sides of the sulcus longitudinalis inferior are found the
_inferior pyramids_, or _pyramidal columns_. These pyramids become
expanded near the origin of the third pair of nerves and merge into the
cerebral peduncles, or crura cerebri.

The pyramidal fibers may also be traced to the optic lobes. The roots of
the abducens are found at a point between the crura cerebri and the
optic lobes. The third pair lies to the side of this, and the roots of
the trigeminus are adjacent to those of the third. A bundle of fibers
from this region pass into the cerebellum and form the crura cerebelli;
others pass into the cerebellum from the side, spreading out in
fan-shaped radiation, and forming the white central substances
peculiarly arranged, called the arbor vitæ, or _tree of life_. A third
bundle fuse with the crura cerebelli anteriorly, and pass into the
peduncles of the cerebrum, or crura cerebri.

The gray ganglionic substance forms columns which extend the whole
length of the medulla oblongata and into the cerebri. The medulla
oblongata contains numerous centers which preside over various visceral
functions as deglutition, respiration, thermotactic, secretory, cardiac,
and digestion.

In the medulla as in the spinal cord there are five main groups of
cells. First, the posterior or upper horns, from which come the somatic
sensory nerves. Second, Clark’s cells, located centrally, which are the
origin of the ganglionated splanchnic nerves. Third, cell groups of the
lateral horns which are the center for the non-ganglionated splanchnic
nerves, and certain other nerves for the viscera, including the enteric
muscles. Fourth, cell groups of the anterior horns, which are the center
of all somatic voluntary muscles. Fifth, groups of single cells probably
belonging to the posterior horns which are probably centers for other
splanchnic nerve fibers.

[Illustration:

  FIG. 77, _A_.

  _G_, A section through the tuberculum bigeminum. 1, Pia mater. 2,
    Nerve fibers. 3, Fine granular ground substance. 4, Thin layer of
    small cells. 5, Fine granular ground substance. 6, A second thin
    cell layer. 7, Fine granular ground substance. 8, Third thin cell
    layer. 9, Fine granular ground substance. 10, Fourth widely extended
    cell layer. 11, A fine granular layer. 12, A thick layer of spindle
    cells. 13, A layer of medullated nerve fibers. 14, Ependemal cells.
    15, The sinus.

  _H_, A transverse section through the medulla oblongata, 1, 3, 4 and 6
    are ganglionic centers. 2, The dorsal groove. 8, The ventral
    fissure. 5, The central canal. 7, Fiber tracts.

  _I_, A transverse section through the cervical portion of the spinal
    cord. 1, Ventral septum. 2, Dorsal septum. 3, The central canal. 4,
    The dorsal horn. 5, The ventral horn.

  _J_, A section through the wall of the oil gland, or rump gland. 1,
    The stroma. 2, The tubular glands some of which are branched.

  _K_, A section through a spike of a comb of a cock. 1, The epithelial
    layer. 2, A dense fibrous subepithelial layer. 3, A second fibrous
    vascular layer. 6, A denser central core supporting the large
    arteries and veins. 4, A vein. 5, An artery.

  _L_, A section through a lobe of the wattle of a hen. 1, The
    epithelial layer. 2, A dense vascular layer. 3, A vein. 4, An
    artery. 5, A loose fibrous vascular structure.
]

The _gray matter in the cord_ is in the form of two commas placed with
their backs together with the central canal passing between them. The
central canal is located in the center of the cord. As the cord nears
the medulla oblongata the form of the gray matter changes. The second,
the third, and the fifth ganglion centers are arranged laterally, and
show a distinct side-horn group. The central canal separates the two
Clark’s columns; later the side-horn group enlarges and extends
ventrally around the anterior horn group and joins on the other side in
half-moon shaped formation.

The _central ganglionic mass of the spinal cord_, the center for the
enteric visceral system, is divided into three complex parts. First,
there are cell groups on both sides of the posterior raphe. Second, the
half-moon shaped ventral groups extending parallel peripherally
described above. Third, lying between groups one and two a complex
group, which possesses a large collection of cells. These furnish
splanchnic nerve centers, the anterior supplying motor nerves and
carrying motor impulses outward, and the superior sensory which carry
impulses to the centers. The cell group of the superior horns takes a
sidewise peripheral position (Gadow).

The _cerebellum_ (Fig. 62, _C_, 2) is located above the medulla
oblongata and posterior to the cerebrum. The cerebellum consists
principally of a median lobe called the worm. The lateral lobes are
conical and rudimentary. The under part of the worm forms the roof of
the fourth ventricle.

On the upper surface of the cerebellum are numerous transverse markings
(in the hen 13 or 14) which divide the lobe into leaves. When the
cerebellum is cut lengthwise there is observed on the sectioned surface
the peculiar arrangement of the white and the gray matter, the arbor
vitæ, mentioned above. There is a small cavity in the cerebellum which
communicates with the fourth ventricle.

The _cerebellar cortex_ shows four parts, namely: First, the central
part composed of white medullated fibers, between which are arranged
neuroglear cells. Second, a rather reddish layer of cells of different
sizes. These cells are embedded in a fine ground substance and are about
0.003 mm. in diameter. Third, a plain layer of large pear-shaped
ganglion cells, the cells of Purkinje. Fine branches extend outward from
the apex of these cells. Fourth, an outer gray layer which consists of
small multipolar nerve cells with some neuroglear cells. The color of
these three layers, according to Gadow, depends upon the color of the
plumage; that is, if the plumage is dark, this layer is dark; if light,
the layers are light. The marked coloring is said to be most distinct in
the second layer.

The anterior portion of the cerebellum consists of medullated nerves
whose fibers run crosswise. These are the extensions of the true
cerebellar fibers, which become fewer and fewer as they proceed
anteriorly. Finally, a few remaining fibers running crosswise fuse as
the commissura Sylvii, and extend into the lobi optici. A layer of nerve
cells extends under these medullated nerve fibers.

A bundle of fibers extending from the medulla oblongata. These fibers
extend into the optic lobes, form the crura cerebri, or peduncles of the
cerebri, and also form the inferior wall, or floor, of the aqueduct of
Sylvius. The crura are sometimes spoken of as the partes pedunculares.
These contain gray matter. The following division is made of the
ganglion of this region. First, a group of cells near the base of the
peduncles, which are divided from the ventral rim by the arciform
fibers. This ganglionic formation may be considered an extension from
the medulla oblongata. Second, a group of the ganglion cells of the
lobus optici. Third, a group of cells lying near the lobus opticus,
which give rise to the ascending roots of the trigeminus. Fourth, a
group of ganglionic cells from which spring the roots of the motores
occuli, and which lies near the middle line and under the sulcus
centralis. Many ganglion cells are found to the right and to the left of
the sulcus centralis, which show different arrangement of the cells at
different levels. Fifth, a group of irregular cells which extends
centrally on the superior walls of the third ventricle and to the
superior part of the lobus opticus.

The microscopic structure of the roof of the lobus opticus, or corpus
bigeminum, shows that the layers are arranged parallel to the pia mater
and are divided into the following parts:

Externally, the pia mater.

An outer layer of very fine nerve fibers, which lies just below the pia
mater.

A layer of fine granular ground substance.

A thin layer of small cells the diameter of each of which is 0.038 mm.

A layer of fine granular ground substance.

A second thin cell layer.

A zone of fine granular ground substance.

A third thin cell layer.

A fine granular ground substance.

A fourth widely extended cell layer.

A fine granular layer.

A somewhat thick layer of spindle-shaped cells.

A layer of medullated nerve fibers.

This last is the inner layer of nerve fiber. On the inner surface of
this layer we find the ependymal cells, the cells that line the cavity
of the optic lobes. The commissura Sylvii form the covering of the lobi
optici and join these two lobes. This commissure is formed from the
upper and the lower layer of nerve fibers. In the commissure these
fibers cross each other.

The _hypophysis_ (Fig. 62, No. _C_, 20) lies back of the chiasm, or
optic commissure, and below the middle of the third ventricle. The
infundibulum, a pedicle-like structure, connects the hypophysis with the
third ventricle of the cerebri. It contains a cavity and forms an
extension of the third ventricle. The hypophysis is divided into two
lobes, an anterior and a posterior.

The _third ventricle_ communicates anteriorly with the lateral
ventricles of the cerebri through the foramen of Monro, and posteriorly
with the fourth ventricle through the aqueduct of Sylvius. The posterior
walls of the third ventricle are relatively thick and form the posterior
brain commissure. The wall is thin from the commissure to the chiasm.
Within it lie two ridges, which connect the two hemispheres with the
corpus callosum, and, farther anteriorly, with the anterior cerebral
commissure. The space from the third ventricle and to the anterior
commissure is called the laminæ terminales.

The _pineal gland_, located between the cerebri and the cerebellum, lies
against the choroid plexus, which covers the highest point of the third
ventricle.

The _cerebrum_ is divided by a deep longitudinal fissure into two
hemispheres. The cerebrum is shaped somewhat like the heart on a playing
card. The lower face is somewhat flattened. The upper and lateral sides
are not provided with convolutions or sulci, but are smooth. The fissure
of Sylvius is faintly marked on the inferior face. The olfactory lobes
appear well developed and are relatively large for the size of the
brain. They lie close together on the extreme anterior portion in the
median line.

The _olfactory cerebral crura_ emerge from the cranium at the upper
angle between the posterior wall, the roof, and the septum of the orbit,
and pass through the olfactory foramina and in grooves on the upper part
of the septum; then passing forward they penetrate the frontal structure
and are finally distributed over the turbinated mucous membrane.

The _corpus striatum_ is large; it occupies nearly the entire floor of
the ventricles.

The _anterior commissure_ is found between the hemispheres. Its middle
part lies in the lamina terminalis on the division between the anterior
and the middle brain, and close to the thalami optici. Its side
extensions are rounded masses called the nervi amygdales.

The _corpus callosum_, quite rudimentary, lies on the posterior dorsal
rim of the anterior commissure.

The _corpus striatum_ forms a thin broad ridge, which passes ventrally.
This structure consists of twenty-five large pyramidal cells which lie
in the posterior lateral dorsal section, and of from ten to fifteen
pyramidal cells which are located in the rest of the section. In
addition to these two groups there are many cells about 5 millimeters in
diameter. These lie, six or more, in a nest imbedded in neuroglia. There
is a thin layer of spindle cells near the ventral line. The outer nerve
nest, or nerves amygdalis, lies in the posterior lateral ventral part.
It is covered by a thin membranous layer. Its cells are pyramidal in
shape and are from 10 to 15 millimeters in diameter. The cells terminate
in spindle form toward the periphery. Nerve fibers extend from the
anterior commissure.

The outer wall of the corpus striatum consists of the following layers:

An outer white layer consisting of fine medullated nerve fibers imbedded
in a ground substance containing numerous nerve cells.

A layer of ganglionic cells, consisting of pyramidal cells from 10 to 15
millimeters in diameter, of other round cells 20 millimeters in
diameter, and finally of cells only 5 millimeters in diameter. This
layer forms a reddish line in the dorsal portion of the corpus striatum.

These layers form part of the median and the posterior cerebral wall of
the lateral ventricle. The lateral ventricle is closed except for a
slit-like opening behind the posterior commissure. This is the foramen
of Monro, through which the lateral ventricle communicates with the
middle, or third, ventricle.

The _choroid plexus_ is found at the base of the lateral ventricle.

The wall of the lateral ventricle becomes thinner near the region of the
transverse commissure on the surface toward the middle brain. At this
point the pia mater and the ependyma, or the lining cells of the
ventricular membrane, form the major part of the wall.

The domestic fowl does not have the hippocampus.

The wall of the middle ventricle consists of an outer white layer, which
is arranged similarly to that of the corpus striatum. The ventral rim of
the wall is formed by a spiral band which consists of fine medullated
fibers, in which are imbedded a few cells.

The _processus cerebri mammillares_ are also called the tubercula
olfactoria. From these structures extend forward the olfactory nerves,
the posterior roots of which may be traced to the walls of the lateral
ventricles.

The structure of the processus cerebri mammillaris is made up of five
layers as follows:

An outer layer, which consists of colorless olfactory fibers extending
in all directions.

A granular ground substance layer, in which are imbedded a few cells.

A thicker granular layer, on the inner edge of which are twenty large
pyramidal cells with processes pointing outward.

A layer of closely packed cells, in which are fine medullated nerve
fibers. These cells are about 5 millimeters in diameter.

An innermost layer of ependymal cells.

Near the hemisphere the peripheral nerve fibers and nerve cells
disappear, leaving only the ground substance of the processus to aid in
the formation of the hemisphere.

There is a long bundle of fibers on the lower surface of the hemisphere,
which blends with the substance of the olfactory fibers.

The peduncles of the cerebrum (Fig. 62, No. 21) are the slightly
diverging columns of nerve tissue, which form the anterior continuation
of the medulla oblongata and disappear under the optic tracts and the
chiasm.


                     THE SYMPATHETIC NERVOUS SYSTEM

The sympathetic nervous system commences anteriorly at the large
superior cervical nerve ganglion. This ganglion, anteriorly, brings into
communication the glosso-pharyngeal, the pneumogastric, or vagus, and
the sympathetic system.

The following nerve trunks emerge from the superior cervical nerve
ganglion: a large trunk fusing with the vagus and directed downward,
accompanying and surrounding the carotid artery; a second large trunk
fusing with the recurrent pharyngeus and the glosso-pharyngeus; a third
trunk which merges with the hypoglossal; finally several trunks which
are distributed to the head.

The _temporo-lacrimalis_, one of the large sympathetic nerves of the
head, as it extends from the cervical nerve ganglion, receives branches
from the ganglion radicis vagi. This nerve, passing between these two
ganglions, extends horizontally forward and outward through a foramen,
crossing the glosso-pharyngeus. Near the Fallopian canals it crosses the
facial nerves, lies supero-laterally, and receives a short branch from
the facial nerve whose fibers are traceable to the geniculate ganglion.
It also receives a branch from the recurrent maxillaris.

This nerve accompanies the external ophthalmic artery forming around it
a network of fibers, called the external ophthalmic plexus. It lies
outside and downward from the optic nerve, sends fine branches to the
external ophthalmic artery and to the masseter artery, and extends along
with a small branch of the superior maxillary nerve to the skin of the
outside rim of the eye cavity.

The _ophthalmic plexus_, a second trunk extending to the head, enters in
its course, anteriorly, the lacrimal plexus. Its fibers also supply the
lacrimal gland, and finally anastomose with the second recurrent branch
of the trigeminus.

The sympathetic _caroticus cephalicus_ nerve, a third trunk extending to
the head, after emerging from the large superior cervical nerve
ganglion, receives some small branches from the glosso-pharyngeal
ganglion, and then enters, in a horizontal manner, a foramen, the
canalis caroticus externus, located in the lower part of the
basi-occipital and the sphenoid bone. The anterior opening of this
foramen, or canal, is close to the posterior part of the pterygoid bone.
Inside this canal the sympathetic caroticus cephalicus receives a small
branch which extends in a straight line from the basal part of the
facial nerve. After receiving this branch, the nerve trunk, passing to
the ear drum, lies close to the petrosum and the sphenoid. It is covered
by the masseter muscle. The carotic ganglion is located at the point of
the fusion of the caroticus cephalicus with the main trunk. At this
point the caroticus cephalicus divides into two branches. The first is
the superior recurrent nerve, which lies close to the upper surface of
the alæ of the sphenoid, passes between the obliquus externus and the
orbital wall, around the eyeball, and finally into the orbital septum
and the internal muscles of the eye. It communicates with the ophthalmic
nerve and sends twigs to the lacrimal gland, the gland of Harder, the
upper eyelid, and the nose. The orbito-nasale ganglion is located where
these nerves communicate near the nasal region. The second branch of the
sympathetic caroticus cephalicus is the inferior recurrent nerve. This
branch passes forward and dorsally from the pterygoid bone to a point
where the upper rim of the rising wings of the jaw bone meets the
sphenoid rostrum. In this course, some branches are given off to the
pharynx, one branch near the lacrimal gland, and a branch which
communicates with the superior maxillary nerve just before the nerve
enters the jaw bone. The spheno-palatine ganglion is at the point of
fusion.

The terminal branches of the spheno-palatine are distributed to the hard
palate, the nose, and the lacrimal gland.

From the large cervical nerve ganglion and near the roots of the
caroticus cephalicus are given off a few small nerve fibers which pass
alone to the pharynx or accompany the jugular nerve branches, and fuse
with the main trunk of the caroticus cephalicus nerve.

From the large superior cervical nerve ganglion the sympathetic trunk
extends downward toward the thorax. It is covered deeply with muscles.
This portion is known as the cervical sympathetic nerve trunk. A trunk
lies on each side of the cervical vertebræ. The large thoracic nerve
ganglion, the inferior cervical, is located along this trunk at the
entrance of the thorax. From this ganglion there is given off the
recurrent cardiacus which supplies the heart. The end branches of the
sympathetic nerve trunk blend with the pneumogastric nerve. The inferior
nerve ganglion is the ganglion cardiacum. Near this ganglion is found a
nerve plexus in which there are imbedded peripherlistic ganglia. This
thoracic plexus, accompanying the collica artery, passes to the
abdominal region, supplying the intestines and taking part in the
formation of the abdominal plexus. The abdominal plexus is located near
the anterior portion of the kidneys. Its fibers are directed mainly
downward to the visceral organs. The large intestine, the rectum and the
copulatory organs receive branches. These latter branches take part in
the formation of the pedunda nerve plexus. Some branches of this plexus,
follow the branches of the posterior mesenteric artery.

The _thoracic trunk_ (Fig. 64, No. 42) of the sympathetic is double. The
anterior portion gives off an anterior splanchnic nerve, or plexus (Fig.
64, No. 43) which accompanies the celiac axial artery to the gizzard and
liver, communicating with the pneumogastric. The posterior splanchnic
nerve is intimately combined with the adrenal body, and the testes, or
the ovary (Fig. 64, No. 45). Intestinal branches accompany those of the
mesenteric arteries (Fig. 64, No. 46). Other branches supply the
kidneys, and communicate with long branches of the spinal nerves
destined for the cloaca and adjacent parts, and thus form a plexus
similar to that found in mammals.


                    FUNCTIONS OF THE NERVOUS SYSTEM

According to function, the nerves composing the trunks are divided into
afferent and efferent.

The _afferent nerves_ are those that convey the impulses from the
periphery of the body to the nerve center, which are located in the
brain or in the spinal cord. The impulses conveyed are those of special
senses, as sight, hearing, taste, touch, and smell. Impulses producing
sensation pleasurable or painful come from the skin, the muscle, or the
viscera.

The _efferent nerves_ are those which convey impulses from the nerve
centers to the periphery. These impulses may be motor as those going to
the muscle cells of the skeletal muscles, the viscera, or the
blood-vessels. These motor impulses make movements in these organs
possible. In the blood-vessel they result in the control of the caliber
of the vessel. These impulses may be of an inhibitory character, as in
slowing the heart. They may be secretory impulses stimulating the gland
to activity or regulating metabolism.

The _ganglia_ are nerve centers which receive and generate impulses; the
nerve trunks are filaments which convey impulses. The gray matter of the
cord described above is the ganglionic portion, and the outer white
matter is made up of nerve fibers which convey impulses from one part of
the cord to another, or to and from the brain.

The nerves that have their roots in the spinal cord superiorly, are
sensory; that is, they convey the sensory impulses from the periphery to
the cord ganglion and to the brain. They have a ganglion just outside
the cord.

The nerves that have their roots in the spinal cord inferiorly; that is,
they convey motor impulses from the nerve centers to the periphery. The
function of the inferior roots is to supply all the voluntary muscles as
well as the oviduct, the intestines, and other hollow viscera, including
the blood-vessels with the power of movement. Many of these fibers pass
to the sympathetic ganglion and are distributed as sympathetic nerve
fibers.

The cord is divided into different tracts, that is, certain groups of
fibers convey certain kinds of impulses.

The superior column of the cord conveys to the cerebrum such impressions
as temperature, pressure, and muscular tension.

The fibers of the lateral columns carry sensations of pain.

The fibers of the direct cerebellar tract carry impulses which result in
the maintenance of the equilibrium of the body.

All the voluntary impulses originate in the cerebrum, pass through the
cerebellum and travel direct to the bulb; they then pass over to the
opposite side, and travel by the crossed pyramidal tract to the
multipolar cells of the inferior horn of the spinal cord, and transmit
the impulse through motor fibers that originate at that point in the
cord.

All sensory impulses enter the brain on the side opposite their origin,
and all motor impulses leave the brain on the side opposite that to
which they are distributed. Injury of the motor area of the right side
of the brain leads to paralysis of the left side of the body.

An impulse of the vasomotor nerve travels in the lateral column of the
cord.

A nerve impulse may originate in the brain and be modified in passing
through a ganglion in the spinal cord or in the sympathetic system.

The system of _reflex action_ is as follows: first, an efferent nerve
which conveys the impulse from the periphery to a nerve center; second,
a ganglion, or nerve center, to receive the impulse and generate other
impulses; third, an efferent nerve to convey the impulse from the nerve
center to the periphery.

The following is an example of reflex action. The foot of a fowl is
pierced with a pin. The sensory impulse is conveyed by sensory nerve
fibers to the nerve centers. In this center the ganglionic nerve cells
generate a motor impulse which is sent back through the motor nerve
fiber to the muscles controlling the part. The result is that the muscle
contracts and jerks the foot.

There are many _functional centers_ located in the medulla oblongata.
Destruction of this part of the system results in instant death of the
bird. In addition to furnishing a path for fibers carrying impulses from
the body to the cerebrum, it furnishes a large number of centers for
such functions as respiration, swallowing, secretion, temperature, and
vasomotor and cardiac activity.

The _function of the cerebellum_ is principally that of coördination. It
brings about harmony and rhythm in muscular movements. If the cerebellum
be removed, the bird can no longer walk. It has lost, with this removal,
all power to coördinate.

The _cerebrum_ of the bird has no convolutions, and the gray, or
ganglionic, portion is thin, indicating low power of intelligence. There
are certain areas presiding over other functions, as motor areas,
sensory areas, and so on.

A careful study of the brain of the fowl shows us that the centers
presiding over sight and smell are well developed.

The olfactory bulbs are the centers of the sense of smell.

The optic thalamus is the center of the sense of sight.

The sympathetic nerve system transmits impulses to the involuntary
muscular structure of all organs, including those of the intestinal
tract, the blood-vessels, and perhaps also the glands.




                              ESTHESIOLOGY


                            THE SENSE ORGANS

The five special senses are seeing, smelling, tasting, hearing, and
feeling.


                           THE ORGAN OF SIGHT

The sense of sight in the bird is well developed. The eye (Fig. 26, _D_,
_E_ and _F_), the organ of sight, is relatively large, round laterally,
and rather flattened antero-posteriorly. It is located at the side of
the head. The eyeball is only slightly movable. The septum interorbital
separates the two eyeballs laterally. As in mammals, the eyeball has
three coats, which are from inside to outside, the retina, the choroid,
and the sclera. The =sclerotic coat= is completed anteriorly by the
cornea with which it forms a union called the _corneo-scleral juncture_.
Around the cornea the sclerotic coat contains a ring of osseous scales
varying in number from twelve to twenty. The sclera may become ossified
posteriorly, forming an osseous sheath around the optic nerve. The
_pecten_ is a vascular comb-like membrane stretching from the nervous
opticus to the crystalline lens. The choroid coat is always black. The
pupil in the hen is also black and round. The iris contains striated
muscular fibers. The _membrana nictitans_, located at the inner angle is
well developed. It is moved by two muscles (Fig. 26, No. _B_, 7, 8, 10).
The lacrimal gland and the gland of Harder are present. There is no
meibomian gland.

The _tears_ are secreted by the lacrimal gland and are drained away from
the fore part of the eyeball by two small canals which extend into a
lacrimal sac. From this sac there extends a tube into the nasal cavity
called the lacrimal duct.

The lower lid is the larger and often incloses a small cartilaginous
plate. The _conjunctiva_ is a true mucous membrane which covers the
anterior portion of the eye cavity attaching to the cornea-scleral
juncture.

The =choroidea= is rich in pigment. On its inner surface lies the dark
pigment layer of the retina. The corpus ciliare, that part of the
choroid coat bearing the ciliary processes, consist of numerous folds.
The ciliary muscles are arranged obliquely. Each consists of three
digitations.

The _iris_ is covered on the posterior side with pigment, the color of
which determines the color of the eye. The yellow pigment of the iris
has been said to be due to carotin and xanthophyll and the black pigment
to melanin. The enlarging and the contracting of the pupil is brought
about by muscles. The reduction of the pupillary caliber is due to the
sphincter pupillary muscle. It is said by some anatomists that the
muscles controlling the caliber of the pupil in the bird furnish
voluntary motion and that the capability of accommodation of the eyes is
greater in birds than in mammals.

The =retina= contains no blood-vessels; otherwise the structure is
similar to that of mammals. The crystalline lens is flattened on the
corneal side and is convex posteriorly. The lens epithelium develops
into fibers in the parts close to the equator, and are almost
perpendicular to the eye axis. The corneal portion is relatively small.

The =sclerotic coat= is dense and white. It is divided into three
layers. It is thin and flexible, and somewhat elastic posteriorly. It
has an internal layer of hyaline cartilage. Anteriorly its form is
maintained by the circle of osseous plates mentioned above. These
plates, interposed between the exterior and the middle layer, are
located immediately behind the cornea. The scales are thin and of oblong
quadrate shape, being elongated from before backward.

The choroid coat is a membrane loosely cellular and highly vascular. It
is impregnated by a black pigment. Opposite the bony circle the choroid
separates into two layers. The external layer is the thinner and adheres
at first firmly to the sclerotic; it passes forward to become continuous
with the iris. The inner layer is thicker than the external. The two
layers are made up of radiating fibers which terminate anteriorly in the
ciliary processes, the ends of which are adherent to the capsule of the
crystalline lens.

The iris is delicate in structure. It is composed of a fine network of
interlacing fibers.

The ciliary nerves and blood-vessels run in the form of single trunks
between the choroid and the sclerotic, and terminate anteriorly in a
ring-shaped plexus for the supply of the iris and the muscular circle of
the cornea. As stated before, the pupil in the fowl is round, but in the
goose it is elongate transversely; and in the owl, a vertical oval.

The optic nerve approaching the sclerotic coat becomes altered into a
conical extremity, which enters a sheath and is directed downward and
obliquely forward. The extremity of the optic nerve in the interior of
the eye presents a white narrow streak. Branches of the opthalmic artery
enter the eye between the lamina of the retina, along the whole extent
of the oblique slit, and penetrate the fold of the pecten upon which
they form a delicate ramification.

The crystalline lens is of soft texture. It is inclosed in a capsule and
is nearly round. It adheres very firmly in the depression in the
anterior part of the vitreous humor. The capsule is lodged between two
layers of hyaloidea, which as they recede from each other, leave around
its circumference the sacculated canal of Petit.

The cornea is of horny consistency and is transparent. Light thus
rapidly passes through it to the posterior part of the eye.

The vitreous chamber, lying back of the crystalline lens, contains a
clear jelly-like substance.


                          THE ORGAN OF HEARING

The ear, the organ of hearing, has in the fowl no conchal cartilage. The
_external auditory meatus_, or canal opening, is found on each side of
the head, and is usually guarded by a few stiff, short feathers. In some
kinds of birds these feathers are capable of being erected so as to
direct the waves of sound into the inner ear. The outer entrance of the
ear contains glands. This canal is short. It leads to the drum, which is
somewhat convex from the outside, and which has a membrane forming a
complete curtain stretched over the outer part. The irregularly formed
drum has connection with the air-containing cavity of the skull, and by
a thin cartilaginous canal, the Eustachian tube, with the pharynx. The
_auditory ossicles_ are represented by only a single bone, called the
_columella_, which most closely represents the stapes of mammals. This
is attached by processes of cartilage to the tympanic membrane. Owen
considers these cartilages as representing the malleus of mammals.
Huxley on the other hand considers them to represent the incus.
Originating from the processes is a small muscle which is attached to
the drum. This is by Shufeldt considered the Tensor tympani. The drum
cavity through the fenestra vestibularis and cochlearis is connected
with the labyrinth.

The =inner ear= consists of a membranous labyrinth, surrounded by a
spongy bony structure—the bony labyrinth. In it are recognized the
vestibulum, the three half-circle shaped canals, and the cochlea. The
superior semicircular canal is the largest. The acoustic nerve enters at
the end of the canals near the ampullæ. The nerves are supported in
delicate vascular membranes lining the canals and slightly projecting
into the ampullæ.

[Illustration:

  FIG. 78.—Diagram of the inner ear. 1, The integument. 2, The superior
    semicircular canal. 3, The external canal. 4, The horizontal canal.
    5, The ampulla. 6, The obtuse osseous conical cochlear cavity. 7,
    The Eustachian tube. 8, The tympanum. 9, Filaments of the auditory
    nerve.
]

The =vestibulum= is a small irregular cavity which communicates with the
arcades and the cochlea, and through the fenestra vestibularis with the
drum cavity. The endolymph of the vestibulum contains microscopic
crystals of calcium carbonate. The semicircular canals are relatively
larger and thicker than in mammals. The ampullæ in the upper and back
part are separated by walls. The cochlea is an obtuse conical tube-like
structure slightly curved at the blind extremity with the concavity
directed backward. It contains a membranous lining. At this point the
cochlea is broadened and accommodates a branch of the auditory nerve.
This nerve spreads out in fine filaments upon the surface of the tubes.
The hollow space of the cochlea is divided by a spiral partition, making
two chambers, the scala vestibuli and the scala tympani. These walls
extend from the beginning of the cochlea.

The =tympanic cavity= is formed by the occipital, the basi- and
alisphenoids, the petrosal portion of the temporal bone. It represents
the stapedial canal leading to the foramen ovalis and the pneumatic
apertures by which the air from the Eustachian tube is conducted to the
precranial diploë.


                           THE ORGAN OF SMELL

The nose is the seat of the peripheral portion of the organ of the sense
of smell. The terminals of the olfactory nerves, which receive the
impressions of odors, are broadened in the mucous membrane of the walls
of the anterior nares. There are no ethmoidal volutes, or sieve-like
structure, in birds. The nerve extends from the anterior portion of the
brain in cone-shape, finally dividing into filaments which are
distributed over the mucous surface of the turbinated bones.


                           THE ORGAN OF TASTE

The most important part of the organ of taste is the _tongue_. In birds
the dorsum of the tongue is covered by a thick stratum corneum, a heavy
layer of stratified squamous epithelium. The tongue, therefore is not in
birds so well adapted for the perception of taste as it is in mammals.
The lingual branch of the trigemini is lacking in birds. This fact makes
the ninth pair, or the nervi glosso-pharyngei, the exclusive nerves of
taste. There is an opinion ventured by one anatomist that, since the
first and the second branch of the fifth pair, or trigemini, have
terminal filaments in the hard palate, they may furnish fibers for the
sense of taste. There are many taste cells on the tongue and on the
dorsal palate.


                           THE ORGAN OF TOUCH

The peripheral parts of the organ of touch in the fowl are the skin and
the feathers.

In a few birds special touch and taste perception can be supplied by the
edge and point of the beak.

In the skin of birds are found numerous sensory nerve endings for
tactile sense.

The sensory nerves, which provide the sense of touch, usually terminate
in one of two forms. The first are the Herbst’s bodies, which in many
respects are similar to the Picinian bodies.

Herbst’s _touch corpuscles_ are found on all parts of the skin; they are
especially numerous in the region of the tail and of the wing. In the
wing they are particularly numerous in the region of the flight
feathers. They occur in large numbers in the periosteum of the anterior
tibial region and in the mucous membrane of the cloaca and of the
generative organs. They are numerous in the conjunctiva and on the
surface of the tongue. They are also found in the gums and in the beak.

Herbst’s corpuscle is made up of a central fiber-shaped part with a
smooth extension of the axis cylinder of its nerve (Fig. 29, _G_). This
central fiber is surrounded by a peculiar protoplasmic body. Outside of
this there is a double row of cubical cells which surround the axial
part. These are close together. Outside of these there occurs a
concentric lamellar layer, which contains cells. In the periphery these
lamellæ become more distinct and contain larger but fewer cells. The
capsule is made up of very thin layers, which are continued into the
perineural layer. Each body contains a thin outer zone. The nerve fiber
passes in a regular manner from the axis cylinder, the myelemma, and the
sheath of Schwann, and as a delicate nerve twig is surrounded by a
sheath consisting of several perineural layers. As it enters the center
of the touch corpuscle, it loses its myeline sheath near the base of the
body, and the terminal fiber becomes flattened. Its rim is directed
toward the two rows of cubical cells, and it ends in a rounded knob.

The touch corpuscles are the largest in the mucous membrane of the
cloaca and smallest in the skin. Hess has found these touch corpuscles
in the large filiform papillæ on the side of the tongue and a few on its
lower surface. They are also found in the soft skin of the edges and
inner borders of the beak.




                        STRUCTURE OF APPENDAGES


The _skin of the fowl_ is very thin and does not contain oil glands or
sweat glands. In the fowl the oil is supplied by a tail or rump gland,
the _glandula uropygii_ (Fig. 35, No. 16). This gland is round or oval
in shape, and about the size of a pea and consists of two lobes. It is
of the tubular variety with a teat, which, in most instances has two
openings. A medium septum divides the gland into two halves. The oil
secreted by the columnar epithelial cells is collected in a body cavity
located in the center of the gland; this has a duct extending to the
surface. The bird by squeezing out a quantity of this oil into its beak
oils the feathers, passing the beak over them, one by one. The oil
renders the feathers practically impervious to water. It is necessary
for the bird to give proper attention to its plumage in order that the
feathers appear in prime condition. Should there be a disease of the oil
gland, or should the bird become ill and neglect its toilet the result
is an unkempt appearance of the plumage, the feathers becoming rather
rough and more or less injured by the weather.

The _subcutis_ is well developed and furnishes to the cutis great
capability for movement, which is necessary for the rising and falling
of the feathers. The corneum is very thin. Papillary bodies are present
only in a very few places, such as the region about the eye and on the
toes. Where the toes touch the ground in walking there are large
wart-like thickenings of the epithelium. In most birds the shanks are
unfeathered. The epidermis on the feathered parts of the skin is thin,
dry on the surface, and abounds in continuous scales. The stratum
corneum is very thick on the horny sheath of the beak, on the top of the
toes, on the spurs of the cock, and on the scale plates that cover the
skin on the shanks. The feathers of birds serve the same protective
purpose as hair on mammals. In cold weather the skin muscles controlling
the feather movements contract; thus the feathers become ruffled much as
we observe the hair standing erect on horses under similar conditions.
By increasing the dead air space around the body, the radiation of heat
is retarded, and the body kept warmer. The corneum of the skin is not
usually rich in blood-vessels; however, in the domestic fowls there is
in the comb, in the wattles, and similar appendages of the head, a thick
vascular network.

The _beak_ and the _claws_ are modified skin; they are true horn
material. At the base of the beak there is often formed scales, which
surround the nostrils, in whole or in part, and have a naked, or waxy,
appearance, which is known as the _cera_.

[Illustration:

  FIG. 79.—Photomicrograph of the section of skin from the sole of the
    foot of a hen. 1, Horny stratified squamous epithelium. _a_, Stratum
    corneum. _b_, Stratum lucidum. _c_, Stratum germinativum. 2,
    Connective tissue supporting membrane, pars reticularis. 3,
    Blood-vessels.
]

The feathers may be considered of two chief kinds, the quill feathers
and the clothing feathers. The most rudimentary of the latter are known
as down. A _quill feather_ consists of two principal parts: the quill,
or calamus, and the vane, or vexillum. The quill is continuous with the
central shaft, called the rachis, the two forming the stem of the
feather. Projecting outward from the stem on each side are a large
number of pointed and very flexible _barbs_. These barbs are located
nearly at right angles to the quill and have extending from them at
right angles smaller processes or _barbules_. These barbules hook
together the barbs and give the web its form. In some feathers, as the
hackle, and in the wing bar feathers of the male of some breeds, there
is a portion of the upper outer edge of the feather not provided with
barbules, which fact gives the feather its characteristic appearance.
The down feathers are loose and fluffy. In this kind of feather the
shaft is weak, and the barbs are not provided with barbules. The barbs
like the shaft may be considered weak. These feathers give great warmth
to the body. There are fiber feathers appearing as hair-like filaments,
and called _filo-plumæ_. These are found scattered over the body; they
are particularly abundant in the region of the head and the neck.

At each end of the quill is a small opening, or _umbilicus_. Inside the
barrel of the feather there is _pulp_, which in young feathers is very
vascular; the vessels entering by the proximal umbilicus are buried,
along with part of the quill, in a papillated follicle of the skin. From
this follicle the feather is developed. At the base of the shaft a
secondary rudimentary quill is usually formed, which may be represented
by a mere tuft of down. On the same general principle the smaller
feathers are constructed. These cover the body, the upper parts of the
legs, and the head, while the larger feathers and quills are confined to
the wings and the tail. The longest quill feathers are those arising
from the hand, called the _primaries_. Those arising from the forearm
are called the _secondaries_. Those that are developed from the proximal
part of the arm are called the _tertiaries_. The rudimentary pollux
carries some feathers which form the _alula_, or bastard wing. The
scapularies are feathers covering the scapula and the humerus. Covering
the bases of the larger flight feathers are wing coverts consisting of
several rows of small feathers. The quill feathers of the tail are
called the _rectrices_. The rectrices have considerable mobility; their
bases are covered by a row of tail coverts.

The pedal digits of the natatores are joined by a membrane, covered with
scaly skin, which forms the web foot.

The feathers in many parts of the body are developed in rows, there
being intervals, or elongated skin areas, between these groups of
several rows, which are not provided with feather papillæ, but which are
covered over by the feathers developed in front of these spaces. The
definite feather lines, or areas, have been called _pterylæ_. The
intervening tracts devoid of feathers are called the _apteria_.

The first outer covering of the bird, or baby chick, is a temporary one
consisting of fasciculi of long filaments of down. These fasciculi on
their first appearance, are enveloped in a sheath, which soon becomes
ruptured and are entirely cast off by the time the baby chicks are ready
to be taken from the nest or the incubator.

[Illustration:

  FIG. 80.—Photomicrograph of the skin of the neck of a S. C. White
    Leghorn hen. 1, The skin possessing an outer stratum, the stratum
    corneum, next the stratum lucidum, next the stratum granulosum and
    underneath the stratum germinativum. Beneath the outer dark band
    representing the upper skin strata is the pars reticularis of the
    derma. 2, Papilla showing from inside to outside the hyaline feather
    wall, the stratum corneum, the Malpighian layer of the follicle, the
    corium. Inside the feather is noted the pulp-like material.
]

The down fasciculi, each emerging from its small quill, are succeeded by
the feathers, which they apparently guide through the skin.

Feathers do not spring from all parts of the body alike; especially
devoid of feathers are those parts where chafing and friction is
greatest, as under the wings and in the groin.

At the end of the quill there is a small opening, the _inferior
umbilicus_, into which projects a papilla of the dermis. Where the quill
emerges from the skin there is another small opening, the _superior
umbilicus_, from which springs frequently a small feather called the
_hyporachis_. The shaft, or _rachis_, has a groove extending along that
surface which lies next the body.

In the newly formed chick the first indication of feathers is the
formation of papillæ, which is constituted by the upward growth of the
dermis, or the sensitive and vascular parts of the skin. Then the skin
immediately around the papilla sinks downward, so that later the papilla
is inclosed in a follicle of the skin. The epidermis over the papilla is
the same as over the rest of the surface. The horny outer layer of the
epidermis forms for the growing feather a protective sheath which is
cast off as the feather is formed. The feather proper develops from the
underlying germinative layer, which as the feather develops, forms a
cylinder of cells. The lower part of the cylinder is in touch with the
papilla; this later becomes the quill (Fig. 80, No. 2). The upper part
of the cylinder develops the web portion of the feather. As soon as the
feather is fully developed the papilla, which has projected into the
quill and nourished it, is withdrawn, and the quill becomes filled with
a pithlike material forming septa, which extend in different directions.

Once a year, usually in the late summer or in the fall, the entire
feather coat is changed. This process is called _molting_. During this
time the bird appears in a somewhat depressed condition, the hen almost
always ceases laying. Birds also molt in the spring, to a limited
extent. The male at this time takes on the so-called breeding plumage,
which is the most beautiful of the year. It has recently been
established by Rice, that the young fowl, in reaching a stage of egg
production, molts five times before the laying period begins.

The =structure of the skin= of fowls is similar to that of the skin of
mammals. The skin consists of two layers the outer portion, or
_epidermis_, and the inner true skin, the _cutis_, _corium_, or
_dermis_. If we study a section of skin from the shank region of a fowl
we find the outer portion is differentiated into two distinct regions,
the rete Malpighii and the stratum corneum. The _stratum corneum_ is the
outer horny layer. The cells making up this portion are fusiform,
flattened, and in regular rows. The nuclei in these layers of cells are
not pronouncedly visible, and the outline of the cells not clear in a
section such as used in our ordinary methods of study. The corneum is a
compact mass of remnant cells which have lost the appearance and their
texture of living cells. It thus becomes modified into scales upon the
skin surface.

Between the stratum corneum and the stratum Malpighii there is another
zone which consists of the cells undergoing a transitional stage from a
cubical shape to a more flattened appearance, and gradually becoming
more granular and hyaline.

The various parts of the epidermis are in close genetic relationship to
one another. The upper layer of epithelium is constantly being
desquamated. This casting off is compensated for by a continuous upward
pushing of its lower elements. Cell proliferation occurs in the basal
cells and in adjacent cellular strata of the stratum germinativum, or
stratum Malpighii, where the elements are often seen in process of
mitosis, or cell division. The young cells are gradually pushed upward.
During their course they assume the general characteristics of the
elements composing the layers through which they pass. This process is
as follows: each cell changes first into a cell of the stratum
Malpighii; then, when it commences the formation of keratohyalin, it
changes into a cell of the stratum granulosum; later still, into a cell
of the stratum lucidum; and finally into an element of the stratum
corneum, where it gradually loses its nucleus, cornifies, and at last
drops off.

The mesodermic portion of the skin consists of loose, subcutaneous
connective tissue containing some fat. The amount of adipose tissue in
the subcutaneous layer is subject to great variation; there are a few
places in which there is little or no fat. The upper portion of this
layer contains a few elastic fibers, which interlace and run in all
directions. Numerous round or oval cells are found in the upper region.
The lower and middle portions of the corium are richly supplied with
blood-vessels terminating into capillaries, which penetrate the portions
bordering the epidermis. Nerves giving off terminal branches also occur.

The various _colors_ of the skins of fowls are due to the distribution
of various quantities of two colors, orange-yellow and brownish-black.

The yellow pigment is probably carotin and xanthophyll, two pigments
contained in association with the chlorophyll of plants, which the bird
obtains in its feed. These coloring matters were formerly called
lipochrome; but as lipochrome may be any coloring matter of fat, it is
not sufficiently definite. This yellow pigment, when present, is
diffused through all parts of the cell. When dilute, it gives a yellow
hue; when concentrated, orange. It is found in the epidermis and in the
fatty masses of and beneath the corium, and is probably identical with
the yellow color of fat in other portions of the body and in the yolk of
the egg. A yellow shank, in a heavily laying hen, soon loses a part of
its pigment; this is also noted of the coloring matter in other parts of
the body. This fact indicates that the coloring matter of the fatty part
of the egg yolk is from the same source as that of the fat. The draught
of this substance is more than normally and the reserve is being drawn
upon. Feed rich in zanthophyll and carotin cause intense yellow colored
yolks, and feeds poor in these substances cause the yolks to be a pale
yellow. Cotton seed meal contains two pigments, one a yellow crystalline
substance and the other a brownish resinous substance. Both of these
pigments are probably deposited in the egg yolk. The eggs of some hens
contain a large quantity giving a light brownish-yellow color to the
yolk.

The brown or black-brown pigment is carried in microscopic pigment
granules, which may be scattered through the ordinary cells or may be
confined to special pigment cells. The former are confined to the
epidermis; the latter may be found in both layers, but infrequently in
the epidermis. When granules are present in the flattened cells of the
corium, they occupy the nuclear region. They lie in short thin lines
while those of the under portion of the Malpighian layer occur in oval
groups. Where these granules occur in the rete layer, they cluster
around the nuclei. In the colored skin there are dark pigment granules
found in the corium and to a less extent in the rete layer. Hanau has
described a definite cellular body which he found densely packed among
the black-brown granules. There is a central body which sends out
branches in all directions. In very dark skinned shanks these ramifying
strands interlace, and form a compact network, which in many cases is so
thick as to give the impression of a homogeneous mass. Here and there
occur round or oval pigmented bodies, which Hanau concluded were the
star-shaped cells with their pseudopod-like appendages contracted.
Pigment cells commonly lie around blood-vessels, clearly indicating
their course. They frequently form a compact tube, but more often are
limited to fragments which only partly enclose the vessels. Pigment
cells occur in several well-defined localities: in the upper portion of
the cutis among the closely interwoven strands of connective tissue; in
the region bordering the blood-vessels; in proximity to nerves, in nerve
endings and in surrounding fat masses. Isolated granules are frequently
scattered throughout the lower section of the corium. Barrows concludes
that the lower bodies of pigment play little or no part in the color of
the external shank, as they lie far below the opaque connective tissue.
Melanin pigment granules are always contained in the pigment cells. When
found in the Malpighian layer, the pigment cells are of an oval form.

Immediately below the epidermis in the shank skin, extends a space less
in width than the row of columnar cells, which is devoid of pigment. The
brown pigment is melanin, which in large quantities takes on a black
hue.

White skin does not contain superficial pigment. Melanin has been
observed in the study of white shank skin, but it lay at considerable
depth or in quantities insufficient to be noticeable. In some breeds of
fowls, as the Mottled Houdan, there are areas in which much melanin is
irregularly deposited, which circumstance gives the leg its mottled
appearance.

The yellow color is the result of a deposit of the yellow pigment in the
fat of the shank. This may be deposited in both layers of the skin, or
in the corium alone. When present it is diffused throughout the entire
cell as well as throughout the intercellular substance. In young birds
the Malpighian layer contains much yellow pigment. Old hens have only
small quantities in the corneum. In breeds with normal yellow shanks old
hens that have never laid eggs show a deep orange color in both the
dermis and epidermis.

In blue shanked birds melanin is present only in the corium. The black
pigment is seen through the semi-transparent Malpighian stratum, making
it appear bluish instead of brown or black.

The black shank color results when melanin appears in the epidermis. Two
forms of black pigment occur in the epidermis: granules in both layers
and pigment cells in the rete Malpighii.

The green shank is produced where there is pigment in the epidermis and
numerous melanin pigment cells in the upper corium. It is an optical
effect due to melanin lying under the semi-transparent yellow epidermis.
There is no melanin in the epidermis.

In the beak the corium of the skin is represented by a thin layer
located between the =periosteum= and the stratum Malpighii. Numerous
blood-vessels pass into it, and in the soft horn-like skin, occur
sensory nerve fibers.

The nails originate from the epidermis, of which they are a
modification. The nails of the toes are bent downward. They present a
convex dorsal surface and are concave ventrally. The dorsal surface
consists of a horny plate, which is set in a nail matrix. The ventral
portion merges with the sides of the upper half, and, as the lower
portion is the softer and wears faster, the nail has a sharp point and
edge. The matrix is formed by a growth of the Malpighian layer of the
cutis. A fold of skin lies over its posterior part. The epidermic cells
of the dorsal, or nail, part, and the base of the ventral part grow
fast. The outer cell layer gradually becomes horn-like.

The _spurs_ are conical with a flat base. The basal part rests upon an
enlargement of the shank bone. Soft structure is found between the horny
spur and the bone. The upper cells, like those of the nails and of the
skin, are constantly being worn or cast off, and new cells push up from
the lower layers of cells. These newly formed flattened cells soon
become cornified. The oldest formation is found at the tip and the
youngest at the base.




                        EMBRYOLOGY OF THE CHICK


That a new individual may be brought into existence, there must be
accomplished the union of the male element, or _spermatozoon_, with the
female element, the _ovum_. This union is called _fertilization_. In the
fowl this fertilization is accomplished at the anterior portion of the
oviduct, after the calyx has ruptured and discharged its yolk, and
before the albumen has been formed around it. The blastoderm is found on
the surface of the yolk. One spermatozoon is all that is required; in
fact, only one can be used in this union.

=Spermatogenesis.=—The spermatozoa are formed by the seminiferous
tubules of the testis. From these cells, called the _spermatogonia_, are
formed other cells called _spermatocytes_, which in turn form the
_spermatids_, the immediate forerunners of the spermatozoa. During the
period of multiplication the spermatogonia divide repeatedly by mitosis.
Numbers of small cells are thus produced, each containing in its nucleus
the number of chromosomes typical of the somatic cell of that fowl. In
the second period the cells become larger and spermatocytes of the first
order are formed. Then comes the period of maturation, during which two
succeeding divisions rapidly occur. The first division results in the
formation of two cells exactly alike. These are spermatocytes of the
second order. They differ from the somatic cells in that they contain
only one-half the typical number of chromosomes. The second division
produces two similar spermatids from one spermatocyte of the second
order. Therefore four spermatids exactly alike may be formed from one
spermatocyte of the first order. From these spermatids the spermatozoa
are formed (Fig. 55). The heads of the spermatozoa contain the nuclei
derived from the spermatids; the necks contain the centrosomes; and the
tail, consisting of three parts is probably formed from the protoplasm.
Three parts of the tail are as follows: first, the pars conjunctionis,
which unites the tail to the neck; second, the pars principalis, which
constitutes the main length of the tail; and, third, the pars
terminalis, which consists of an axial filament which transverses the
entire tail and is surrounded by a protoplasmic sheath.

=Oögenesis.=—The ovum during its formation passes through three stages.

[Illustration:

  FIG. 81.—Section of ovum in a hen. 1. Nucleolus. 2. Nucleus. 3. Liquor
    folliculi. 4. Stratum granulosum. 5. Follicular cells. 6. Theca
    folliculi. 7. Peripheral stroma.
]

The first stage, that of _division_, takes place before the chick is
hatched, and, according to Bradley, comes to an end about the time of
hatching. This stage consists of the rapid formation of ova in the
female chick. In the second stage, which begins about the time of
hatching, there is an increase in the size of the units of the ovary,
accompanied by _yolk formation_. At this time each ovum is in its own
follicle (Fig. 81), and is surrounded by a layer of cuboidal cells and a
_theca_. The theca is formed from the adjacent fibrous stroma. The third
stage, that of _maturation_, commences during the development of the
yolk and is complete after it has escaped to the oviduct. Maturation
consists of each cell’s dividing into two unequal parts. In each
division the cell is split into a small cell known as the _polar body_,
which is cast off and disappears, and a larger cell, which is the ovum
proper. In this process half of the original chromosomes are cast off.

=Fertilization.=—The sperm travels rapidly; experiments have shown eggs
to be fertile laid twenty-four hours after service by a male. When the
ovum is discharged into the ovarian pocket it is surrounded by
spermatozoa.

After the male pronucleus has united with the female pronucleus in the
single-celled ovum, there is a cleavage of the cell in the long axis of
the egg, making two cells; and then a cleavage at right angles, which
progressively continues, makes the mulberry-like mass. The remaining
content of the egg consists of food for the development of the embryo.
From this mass of cells before the egg is laid the _blastoderm_ is
formed. The cells of the blastoderm are differentiated into two layers.
The superficial layer is the _ectoderm_ and the lower layer is the
_entoderm_. In the newly laid egg the blastoderm may be observed. It is
about 4 millimeters in diameter. It has a transparent central area, the
zona pellucida, which is located over the subgerminal region. There is a
peripheral, less transparent area called the zona opaca.

In the fertile egg, as soon as it is subjected to the proper
temperature, cell multiplication in the blastoderm begins. The first
signs of such change are noted in the pellucid area of the blastoderm
where embryonal traces appear in the form of the parallel lines called
the _plicæ primitivæ_, which diverge to form the cephalic dilatation. At
about this time takes place the formation of the _myelencephalous
columns_, in which the blood lakes expand in the surrounding halones and
in the tracts along which pass colorless blood particles. These tracts
extend from below the cephalic expansion to the peripheral sinuses, as
the _proto-vertebræ_, which begin to appear at the sides of the myelon.
The red color is acquired by the blood, and the heart by its movements,
is made more manifest as the _punctum saliens_. A distinct membrane, the
serous layer, is formed upon the germ and the blastoderm. The cephalic
end of the embryo rises from the surface of the blastoderm, and then,
curving down, sinks into it, forming for itself a kind of hood of the
serous layer. This hood gradually extends from the margin of the fossa
over the body, and, meeting a similar fold formed by the projecting and
incurved tail, closes over the germ on the upper side, making a
circumscribed cavity, which is the _amnion_. The progress of
differentiation of layers of the blastoderm has, meantime, gone on
beneath. The serous layer is in part reflected from the vascular and
from the mucous layer. The mucous layer is concerned in the formation of
the intestinal canal; and beyond this part, which is at first an open
groove, the mucous layer expands over the yolk, which it ultimately
incloses, the margins of the _vitellicle_ so formed contracting and
uniting at the side opposite the embryo at a sort of cicatrix, to which
the last part of the abdominal yolk adheres. The vitellicle is richly
vascular, and the surface next to the yolk is augmented by rugæ.

The fowl’s egg, at about the fortieth hour, shows the buds from which
the limbs are developed. A vesicle is seen to protrude near the anal end
of the intestine, which, rapidly expanding, spreads over the embryo,
acquiring a close adhesion to the amnion, but remaining distinct from
the vitellicle, over which it spreads. It finally encloses the albumen
and interposes itself between the latter and the lining membrane of the
shell. Umbilical vessels are associated with this membrane. Hunter
called this membrane the _allantois_ from its containing urine, and Owen
states that the sac which surrounds the albumen acts as the chorion or
_placenta_; for it is most probable that from this surface the albumen
is absorbed and the chick supported on its developmental food. The
external part of the sac apparently acts as lungs as it comes into
contact with the shell of the egg through pores of which there is an
exchange of air. Oxygen is consumed and carbon dioxide is given off. The
blood in the vessels of this membrane is in color more like arterial
blood and that in the interior more like venous blood.

The embryonic mass of the incubating egg always floats to the top side.
As the embryo grows it turns upon its left side, exhibiting a profile
view; it then indents the yolk, and finally almost divides it into two
parts.

The peripheral layers of cells rise from the margin of the germ mass,
and extend and contract toward the opposite pole. This tract of germ
substance is the _primitive streak_. Along the median line it next forms
a furrow, which stops short of the ends of the streak. This streak
terminates opposite the point from which the germ begins, and swells
into the head. The median furrow expands upon it. The cephalic borders
are next united by a thin layer of epithelial cells above the furrow,
converting it into a cavity, or ventricle. The myelonal furrow is
similarly covered by a layer, uniting the lateral columns. The embryonal
trace becomes longer, narrower, and bends round the vitellus. A layer of
epithelial cells forms a network over the whole dorsal surface of the
embryo. Oblique striæ appear in the broadening germ mass radiating from
the primitive streak. These indicate divisional segments. These
beginnings of aponeurotic septa probably accompany and support nervous
productions from the myelon columns.

Two transverse constrictions begin to divide the cephalic enlargements
into three lobes, the second and the third of which expand into
vesicles. An accumulation of cells at the side of the middle expansion
appears to add greatly to its breadth. This forms the basis of the eyes.

The differentiation and the confluence of the cell constituents of the
primitive streak have led to the formation of a pair of albuminous cords
along the sides of the median furrow, forming the _myelon_ proper. The
cells exterior to and above them are converted into muscle and fibrous
septa; and beneath the column is a jelly-filled cylinder, with a
transversely striated sheath, pointed at both ends, forming the
_notocord_. Its anterior point passes a little in advance of the
acoustic vesicle. Beneath the notocord and surrounding the blastema is
stretched the vegetative, or mucous, layer of cells, in contact with the
yolk. Both the head and the tail of the now cylindrical embryo are
liberated from the surface of the yolk. A fold of the blastema,
reflected from the under part of the head, sinks like a pouch into the
yolk, and soon includes the rudiment of the heart, like a bent cord,
which begins to oscillate about the seventh day. From the midline of the
inferior surface of the embryo, or its mucous layer, two longitudinal
plates descend, diverging into the yolk-substance, and form the
_primitive intestinal_ groove.

The _ophthalmic vesicle_ elongates and curves outward until the two ends
almost come into contact. Between these two ends and beneath the
delicate tegumentary layer connecting them the _crystalline lens_ is
formed. About the same time, the _otoliths_ appear in the acoustic
vesicles, which have now acquired a cartilaginous case. The _cerebral
lobes_ begin to be formed by a small fold, rising laterally and
overlapping the forepart of the second enlargement, which has expanded
to greater breadth. The _olfactory cavities_ appear as small cutaneous
follicles.

The two myelonal columns, expanding between the ear sacs and receding so
as to show the notocord beneath, bend upward and inward, and unite, to
be continued into the posterior of the _optic lobes_, thus commencing
the cerebellar bridge across the epencephalic ventricle. The encephalic
vacuities have begun to be filled by the granular basis of the
cerebellar substance.

The _intestinal groove_ begins to be converted into a canal at its two
ends. Beneath the anterior end, and behind the heart, there gradually
accumulates the cellular basis of the liver.

The commencement of the development of the _organ of hearing_ is by a
superficial depression of the cephalic blastema to meet the process from
the encephalon, which forms the acoustic nerve. The lining of the
depression becomes, on closure of the slit, the proper tunic of the
labyrinth.

The vesicle of the labyrinth swells into four dilatations, of which
three are ampullar and the fourth cochlear. The _ampullar dilatations_
extend into very slender canals, at first almost in the same plane, by
which they are brought into mutual communication. As the canals expand
and elongate, they assume their characteristic relative positions as
external, superior, and posterior, the posterior end of the external
canal being extended beneath the posterior canal. The cochlear
dilatation curves as it elongates. An inner layer becomes distinct from
the common membrane and forms the _acoustic lamina_.

As in the development of the ear, so in the development of the eye, the
production of the nerve process from the cerebral center is the first
step; the infolding of the superficial blastema to meet the nerve is the
next. The so-called _cutaneous follicle_ becomes a circumscribed sac or
vesicle, in which the changes and the development next proceed,
converting the vesicle into an acoustic labyrinth or into an eyeball. In
each case neural elements of two vertebræ become modified to lodge and
to protect the sense organs, forming respectively the recess called
_otocrane_ and that called the _orbit_. The one is located between the
occipital and the parietal vertebræ, and the other between the frontal
and the nasal vertebræ. The part of the outer blastemal layer of the
head which sinks to meet the process from the mesencephalic dilatation,
rapidly changes its follicular into a vesicular state. The vesicle thus
formed elongates, bending around the cell mass in which the _crystalline
lens_ is formed, and the meeting of the two ends results in forming the
choroid fissure at the lower part of the eyeball.

The _mesencephalic process_, or optic nerve, expands at the posterior of
the circular sac, and, in the course of mutation into eyeball, lines its
posterior part with a layer which becomes the _retina_. The transparent
layer covering the forepart of that sac and the inclosed lens is formed
into the _cornea_. Other layers of the sac are formed into the
_choroid_, the _ciliary processes_, the _iris_, and the _pecten_.

Of the appendages of the eye the membrana nictitans is the first to
develop. Then develop the lower lid and, last, the upper lid.

After the development of the essential organs of sense, the skin is
developed. Modifications of the skin form the outer ear and the eyelids.
Then are formed the maxillary arch, the hyoidean arch, and the scapular
arch.

The vessels which return the blood from the vitellicle are the
transverse and the longitudinal _vitelline veins_. The first are so
called because these trunks pass to the embryo at right angles to its
axis. They are the largest returning canals. The _longitudinal veins_
extend parallel with the axis of the embryo; they are of smaller size.
The right anterior longitudinal vein becomes the right precaval and
receives the remains of the right transverse vitelline vein, as the
right vena azygos. The left anterior longitudinal vitelline vein is also
persistent as the left precaval, and enters in the mature bird, as in
the embryo, at the posterior or the lower part of the auricle. The left
transverse vitelline vein is also subsequently reduced, by receiving
only the vertebral veins of that side, to the condition of a so-called
azygos vein. The main trunk of the post-caval is the result of the
returning vessels from the abdominal viscera and the posterior limbs at
a later stage of development. There is but one principal posterior
longitudinal vitelline vein, and this anastomoses with the left
transverse vein as it enters the embryo.

The _auricle_, which, by its dilatation of the left side, appears to be
double, receives the venous blood at its right division. The left one,
subsequently receives the veins from the lungs, is ultimately separated
from the left precaval and the right auricle to which that vein is
conducted and restricted.

The _ventricular part of the heart_, at the second day of incubation, is
in the form of a bent tube, curving from behind downward, forward, to
the right and upward, continuing insensibly into the part representing
the aortic bulb, in which the septum first appears, and ultimately
dividing the ventricle into two.

At this stage the piers of the _maxillary arch_ appear as buds from
beneath the eyeballs. The naso-premaxillary process is above their
interspace. The piers of the mandibular arch and those of the hyoidean
arch follow in close succession. The blastemal base of the scapular arch
projects slightly at the sides of the fovea cardiaca; the piers, now
separate, ultimately meet in front of the heart, and accompany it in its
retrograde course. The mesencephalon is the largest of the segments of
the brain which are connected with the eyeballs.

When the heart has assumed its form as such, distinct from the great
trunks rising from it, the two _arteries_ from the base of the
ventricles appear. The artery to the right bifurcates, one division
supplying the head and the wings, the other winding over the right
bronchus. That to the left also bifurcates. Its left division arching
over the left bronchus and anastomosing with the right arch a little
below and behind the apex of the heart. Its right division arches over
the back of the heart, bending to the right and anastomosing with the
right aortic arch just above the outer ductus arteriosus. Each of these
divisions of the left primary arterial trunks sends off a branch to its
corresponding lung. As the lung expands, and especially at the beginning
of the act of expansion toward the close of the period of incubation,
the blood is diverted into the pulmonary vessels, and the channels below
them shrink and disappear. The left primary artery is retained as the
trunk of the pulmonaries, and, through the changes in the interior of
the ventricle, this artery comes to discharge exclusively the ventricle
corresponding to the right in mammals. The retained aorta rises from the
left ventricle.

The _air-sacs_ begin at the lower point of the lung, appearing like
small hydatids, and extend further and further into the abdomen, in
front of the kidneys. They are at first full of fluid. Soon after the
development of the abdominal air-sacs others are developed.

The _lungs_ are at first free, but afterward begin to be attached to the
ribs and to the spine.

In the female embryo we first observe two _oviducts_, one on each side
of the basis, or stroma of the ovarium, which appears in a relation to
the primordial kidneys similar to that of the testes in the male. At the
period when the permanent kidneys have sent their ureters to the cloaca,
the oviducts have been developed as prolongations from that part, and,
up to a certain point of development, they are of equal size and length.
Subsequently the left oviduct alone continues to grow; the right
remaining stationary or shrivels; occasionally it may be discerned as a
rudimentary in the mature bird, but usually all trace of it has
disappeared before hatching. The left oviduct expands above or at its
free end into the infundibular orifice, where its parietes are very
thin. As it descends, these increase in thickness, and the efferent tube
gradually acquires the texture and form of an intestine. It is attached
and supported by a duplicature of the peritoneum.

[Illustration:

  FIG. 82.—Embryological studies.

  _A._ 1, The chorion and allantois. 2, The allantoic cavity. 3, The
    amnion. 4, The yolk sac. 5, A small quantity of remaining albumin.

  _B._ Brain tube of a chick 25½ hours old showing partly closed brain
    tube with eleven folds of neuromeres.

  _C._ The development of the alimentary tract. 1, Trachea. 2, Lung. 3,
    Esophagus. 4, Stomach. 5, Pancreas. 6, Bile duct. 7, V-shaped loop
    of midgut. 8, Cloaca. 9, Vitello-intestinal duct.

  _D._ 1 to 6 inclusive, same as C. 7, Cæca. 8, Cloaca.

  _E._ Kidneys, Wolffian bodies, and testes of an embryo chick. 1, The
    adrenals. 2, The genital. 3, Primitive oviduct. 4, Permanent kidney.
    5, Ureters. 6, Duct of primitive kidney which conducts the excretion
    into the cloaca.

  _F._ A transverse section of a chicks’ head 48 hours of incubation. 1,
    Forebrain. 2, Pigmented layer of retina. 3, Ectoderm. 4, Nervous
    part of retina. 5, Optic stalk. 6, Invagination of ectoderm to form
    the lens rudiment.
]

At first, the right and the left ovaria are similar in size, but the
symmetry is soon disturbed by concentration of development in the left
ovary. The right ovary remains stationary and ultimately, in most birds,
completely disappears by the time the chick is ready to emerge from the
shell.

Three fetal membranes are developed, the _chorion_, the _amnion_, and
the _allantois_. There is also developed the _yolk sac_ (Figs. 82 and
83). The amnion is connected to the body wall at the umbilicus. The
amniotic fluid is found in this sac. The chorion is at first surrounded
by the albumen, but as the albumen is absorbed the chorion comes in
contact with the inner shell membrane. It is probable that the chorion
consists of ectoderm on the outside and of mesoblast on the inside. The
amnion, on the other hand, is formed of mesoblast on the outside and
ectoderm on the inner, or embryonal, side. The allantois springs from
the embryo soon after the fourth day, and develops from the ventral wall
of the primitive gut. By some embryologists, the yolk sac is included in
the embryonic membranes. It commences as the splanchno-pleure
surrounding the mass of yolk. It becomes smaller as the yolk is
absorbed. At first its outline is round but later its walls become
folded in. The yolk is dissolved and absorbed by the entodermic lining
of the sac, and is carried to the embryo by veins called the vitelline
veins (Fig. 83, No. _B_, 4), which ramify on the walls of the sac.

Some time after the fourteenth day, the chick assumes a position
lengthwise within the egg shell so that the head is near the broad end
of the egg. The head is bent upon the chest and the beak is usually
tucked under the wing. Later the head assumes a position, by a double
curve of the neck, so that the beak is in contact with the air cell.
About the fifteenth day, the coils of intestine, which heretofore have
been outside the abdominal cavity, are withdrawn into the abdominal
cavity, as is also the abdominal yolk sac. As the chick pips out of the
shell, the umbilicus becomes occluded.

The outer upper part of the tip of the beak is provided with a short,
stout, spike-like arrangement, called the _egg tooth_. On the twentieth
day this part of the beak is forced against the wall of the egg and
gradually breaks through the egg shell. The breathing by the lungs
commences some time before hatching; this is evidenced by the chick
within the shell giving chirping sounds.

[Illustration:

  FIG. 83.

  _A._ Longitudinal section of chick, 4 days incubation. 1, Cephalic
    fold. 2, Caudal fold. 3, True amniotic cavity. 4, Epiblast. 5,
    Somatic mesoblast. 6, Visceral mesoblast. 7, Hypoblast. 8, Future
    anua still closed. 9. The allantoic vessicle. 10, The mesentery. 11,
    Intestine. 12 and 13, Yolk sac. 14, Cavity of true amnion. 15, The
    mouth. 16, Pleuroperitoneal cavity. 17, Fore gut.

  _B._ Membranes of the chick at the third day of incubation. 1,
    Membrane surrounding albumin. 2, Amnion. 3, Allantois. 4,
    Vitellicle.

  _C._ The fore part of an embryo chick at the second day. 1,
    Mesencephalon. 2, The eye. 3, Olfactory organ. 4, Mandibular arch.
    5, Maxillary arch. 6, Maxillary arch. 7, Hyoidean arch. 8, Scapular
    arch. 9, Depression organ of hearing. 11, Process from encephalon
    for union with nerve of hearing.

  _D._ Primitive blood-vessels at second day of incubation (Owen). 1,
    Mesocephalon. 2, The right anterior longitudinal vein. 3, The eye.
    4, The mandibular arch. 5, The hyoidean arch. 6, Scapular arch. 7,
    The same. 8, The ventricular portion of the heart. 9, The right
    transverse vitelline vein. 10, Posterior longitudinal vitelline
    vein. 11, Vertebral vein. 12, Tributaries of same. 14, The auricle.
    16, Aortic bulb.

  _E._, A transverse section of chick embryo, 29 hours incubation. 1,
    Neural canal. 2, Neural crest. 3, Somatopleure. 4, Splanchnopleure.
    5, Omphalomesenteric vein. 6, Aorta. 7, Notocord. 8,
    Pleuroperitoneal cavity.

  _F._ Chick embryo at the ninth day of incubation. 1, Allantois. 2,
    Amnion. 3, Air cell at large end of the egg. 4, Egg shell. 5, Outer
    shell membrane. 6, Inner shell membrane. 7, Yolk sac. 8, Albumin
    (Bradley).
]

The _circulation of the blood_ is somewhat like the circulation in the
fetus of quadrupeds. The primitive tubular heart (Fig. 83, No. _D_, 8)
is bent in S-shape; the two ends are connected with blood-vessels; and
later, by the development of the septa, the cavities of the adult heart
are defined. The foramen ovale is found in the median septum. This
opening brings the right and the left side into communication. The septa
between the cavities of the heart are completed by the end of the sixth
day. The two vitelline, or omphalo-mesenteric, veins carry the blood
containing the nutrients from the yolk sac to the liver, where it is
mixed with the blood drained from the intestines by the portal vein, and
this blood is finally carried by the posterior vena cava into the right
auricle of the heart. From here it passes through the foramen ovale to
the left auricle; from the left auricle it enters the left ventricle,
from which it is forced into the aorta, and then out into the systemic
circulation. Practically all, if not all, of the blood of the pulmonary
artery is sent into the aorta through a connection with this vessel
called the ductus arteriosus.

_Down_ appears about the thirteenth day of incubation. There are two
kinds of down on the chick, one long, which comes first, about two or
three days before hatching; a second, or fine, down forms at the roots
of the other. As the embryo develops the air cell, at the large end of
the egg which is developed between the two shell membranes, or _membranæ
putaminæ_, gradually enlarges.




               OUTLINE FOR LABORATORY STUDY OF THE CHICK


  The objects of laboratory study of the embryos are as follows:

  1. To study the living embryo.

  2. To study the entire embryo:

          With the dissecting microscope, as an opaque object.

          With the compound microscope after killing, hardening,
          clarifying, and mounting.

  3. To study embryos by dissection, in later stages.

  4. To study the serial sections with the compound microscope.


                           THE LIVING EMBRYO

The egg is opened under warm physiological salt solution: 0.8 per cent.
sodium chlorid in distilled water heated to a temperature of 38°C.

Gradually pick away the shell at the large end. Note that there are two
membranes and an air cell. Strip off the membranes. When sufficient
shell and membranes have been removed from the large end, invert the
open end of the egg in the salt solution and allow the contents to flow
out. Care must be taken not to break the yolk. The embryo, or
blastoderm, lies upon the surface of the yolk, which is usually turned
with this body uppermost. Separate the blastoderm by cutting around the
outside of the area vasculosa. In doing this a small pair of slightly
curved scissors is needed. After the embryo, or blastoderm, has been
separated, gently float it into a watch crystal with the flat bottom
submerged in the salt solution. The watch crystal with its contents may
now be gently lifted out. Next remove the vitelline membrane. The
vitelline membrane is the delicate transparent membrane covering the
blastoderm, The embryo is now ready for study.


        THE PREPARATION FOR STUDY OF ENTIRE EMBRYOS AND SECTIONS

The following processes may be used in killing embryos up to four days,
or ninety-six hours, of age. After removing the embryo as described
above, spread the blastoderm out in the watch crystal and pipette off
the salt solution. Allow it to stand till the edge of the tissue begin
slightly to adhere. Then slowly add the killing fluid by aid of a
pipette, dropping it on the center of the embryo. The pipette must be
held low or the mechanical interference will dislocate the parts.

Older embryos are submerged with their membranes intact into the killing
fluid. The quantity of fluid should be several times the bulk of the
specimen. Kleinenberg’s picrosulphuric acid may be used as a killing
fluid. This fluid is a saturated solution of picric acid plus 2 per
cent. sulphuric acid, to which is added twice its volume of water.

Chick embryos from one to two days old should be left in this fluid from
one and one-half to six hours. Embryos from two to four days old two and
one-half to six hours. Remove the specimen from the killing fluid, and
place it in 70 per cent. alcohol. Change the alcohol every twenty-four
hours until the color ceases to come out of the embryo. Preserve in 80
per cent. alcohol.

If the specimen is to be mounted whole, transfer it from 80 per cent.,
then to 50 per cent., then to 35 per cent., and, finally to water. Small
embryos should remain in each fluid thirty minutes and large ones sixty
minutes.

The following method may be used for _staining embryos_: Dilute
Delafield’s hematoxylin with four times its volume of water. To every 6
cubic centimeters of this diluted hematoxylin, add one drop of
Kleinenberg’s undiluted picrosulphuric acid, and leave specimen in the
fluid thus prepared until it is stained through. This will require from
one to three hours. Now pass up through the series of alcohols to 70 per
cent. Next extract the excessive stain with 1 per cent. hydrochloric
acid in 70 per cent. alcohol. Wash repeatedly with 70 per cent. alcohol
to free from the acid; then transfer the specimen to 80 per cent.
alcohol and leave in this for several hours for complete removal of the
acid; then transfer to 95 per cent. alcohol for thirty minutes. Allow
the specimen to remain in absolute alcohol for one hour. Introduce a
layer of oil of cloves or xylol beneath the alcohol. This may be done by
gradually allowing the fluid to run down the side of the bottle. After
the embryos have sunk into the oil and begun to appear transparent,
remove the fluid and add fresh oil. After the specimen is sufficiently
transparent, mount in balsam, supporting the cover slip so that it will
not rest on the embryo.

In staining for section, place the embryo in borax carmine from the 50
per cent. alcohol and leave twelve hours. Then wash in 50 per cent.
alcohol; after which transfer to 70 per cent. alcohol for six hours.
Clarify in oil of cedar or oil of cloves, and place in melted paraffin
for two hours. Imbed in paraffin, and section.

Embryos may be hardened, imbedded, and sectioned after the usual
methods, using either paraffin or celloidin, and the sections stained
with hematoxylin and eosin after sectioning.


                   POINTS TO BE OBSERVED IN THE STUDY

1. THE EMBRYO TWENTY-NINE TO THIRTY-FOUR HOURS OLD WITH FROM TEN TO
FOURTEEN SOMITES.

A study of the egg.

In opening the egg, observe that the shell membranes are double.

Observe that the shell is porous.

Note the air cell at the large end of the egg and note that the space or
cell lies between the outer and the inner shell membrane.

After the egg contents have dropped into the salt solution, note
extending from the ends of the yolk the twisted denser cords of albumen.
These are the chalazæ, which act as stays to the yolk. Note that the
yolk is surrounded by a delicate membrane. This is the vitelline
membrane. The yolk is the true ovum and serves as food for the
developing embryo.

A study of the living embryo.

Note the amount of yolk that is covered by the blastoderm. Note the
slipper-shaped, transparent center of the blastoderm. This is the area
pellucida. In the center of this there is a narrow white streak. The
area opaca is the area lying external to the area pellucida. In this
there is the area vasculosa.

A study of the embryo entire, including the vascular area.

The blood islands show as irregular deeply stained masses in the
vascular area. At this stage they are inclosed in wide anastomosing
tubes, the extra-embryonic blood-vessels, which open peripherally into
the bounding sinus terminalis.

The following structures may be identified:

The neural tube forming the axis of the embryo. In the anterior region
may be noted the forebrain, the optic vesicles, the midbrain. The
hindbrain is subdivided into the neuromeres. The cord, or myelon, of the
neural tube back of the hindbrain is closed in front but is open behind.

The head projects above the blastoderm. The fold which unites the
ventral surface of the head with the blastoderm is called the head fold.

The diverging folds of the myelon encloses the primitive streak.

On each side of the neural tube are the mesoblastic somites. The series
is continued behind by the undivided segmental plate.

The heart is beneath the hindbrain. The portion of the body cavity in
which it lies, is bounded in front by the head fold and behind by the
diverging limbs of the splanchno-pleure. Its posterior or venous end
receives the vitelline veins from the vascular area. The anterior or
arterial end is prolonged into the ventral aorta.

Note that the axis is somewhat bent.

The head fold of the amnion is noted to extend over the anterior end of
the head.

A study of the transverse sections.

The sections about 20 micro-millimeters thick should be cut serially,
and so mounted. Knowing how many micro-millimeters the embryo is in
length will enable one to make a diagram of the fetal structure in the
study of the series of transverse sections. The sections should be drawn
in the order studied so as to obtain relative structural ideas.

With the microscope study the following regions:

1. Optic vesicle.

2. Midbrain.

3. Posterior half of the heart.

4. Myelon in the closed region.

5. Myelon in the open region.

6. Through the primitive streak.

2. THE EMBRYO TWENTY TO TWENTY-FOUR HOURS OLD WITH FROM TWO TO SIX
SOMITES.

Compare the parts in this embryo with those of the embryos from
twenty-nine to thirty-four hours old. Note and describe the relations of
the embryo, the area pellucida, and the area opaca. Note how much of the
yolk the blastoderm covers.

In studying the entire embryos, note the condition of the medullary
plate. Observe if the tube is formed in any part; how far back the head
plate extends, if the heart can be seen; and if the primitive streak is
longer or shorter than in 1.

Study relations of structures and make drawings through the point of
divergence of the walls of the fore gut; also through the somatic
region, and through the primitive streak.

Study all parts, as the head fold, the heart, and the fore gut.

3. THE EMBRYO FORTY-FOUR TO FORTY-EIGHT HOURS OLD WITH TWENTY-FOUR TO
TWENTY-NINE SOMITES.

Remove the embryo with the entire area, and preserve it.

Note and carefully describe the changes visible to the naked eye since
the thirty-fourth hour.

In making a study of the entire embryo we note there has been a rapid
growth of the dorsal surface of the head, which has become more bent.
This bend, in the region of the midbrain is called the cephalic flexure.
The forebrain and part of the midbrain form almost a right angle with
the rest of the head. The head is compressed laterally and free from the
blastoderm. The dorsal side of the trunk is turned up, and there is a
twisting of the axis of the embryo just back of the heart. The tail fold
begins at about this time and may or may not be visible. The optic
vesicles are relatively smaller in relation to the brain than in 1. Note
the part of the forebrain to which they are attached. Observe the inner
and outer layers of the retina, the lens, the choroid fissure, and the
cavity of the vitreous humor.

Note the auditory vesicles and whether or not they are closed sacs.

Note that the heart has grown in length and has become doubled on
itself. The two ends are fixed. Note the relation of the heart to the
afferent and efferent blood-vessels. Note that two, and possibly three,
visceral pounches are visible. Note whether or not they are ventral to
the midbrain. The first, the hyomandibular pouch, is bounded in front by
the first visceral, or mandibular, and behind by the second visceral,
arch. The second pouch is bound in front by the hyoid, and behind by the
third visceral arch. The third pouch is bounded in front by the third
visceral arch, and behind by the fourth. Note the number of mesoblastic
somites and the condition of the mesoblastic segmental plates.

Note how far back the foregut is closed. Locate the head fold of the
amnion, and note how far back it is closed. Note changes that have taken
place in the vascular area. In studying the sections it will be found
that a section cut transversely to the trunk will pass horizontally
through the forebrain and through the midbrain.

Study a section through the trunk a short distance behind the heart.
Observe the elevation of the axis of the body. Note the way in which the
lateral folds, or the lateral limiting sulci, in the somatopleure,
delimit the embryonic from the extra-embryonic area.

Note the appearance of the mesenchyme, the approximation of the two
dorsal aortæ, the appearance of the amniotic folds. Observe in the
mesoderm the posterior cardiac veins, and the myotomes, or muscle
plates. The sclerotome is made up of the mass of mesenchyme between the
myotome, on the one hand, and the neural tube and the notochord, on the
other. Note the folding of the splanchno-pleure, and note if there is
present the Wolffian duct, or the nephrotome.

Study sections through the optic vesicles. Note if there is the
beginning of the lens. Do you note the diverticula of the pharynx? Can
you identify the closed amnion and the chorion?

Study sections through the auditory pit. Note fusion of the gill pouches
with the ectoderm. Note the blood-vessels. Study sections through the
region of the heart, through the roots of the vitelline veins, and
through the primitive streak, if it is still present.

For this study it will appear that the anterior end has developed in
advance of the posterior end. The tail fold has probably just begun.

Write a description of the pharynx, and of the circulation at this
stage.

4. THE EMBRYO SIXTY-EIGHT TO SEVENTY-TWO HOURS OLD WITH CERVICAL
FLEXURES FORMED.

In a study of the living embryo note the changes visible to the naked
eye since forty-eight hours old. Note the difference in the
blood-vessels of the vascular area. Name the arteries and veins. Note
the beating of the heart.

In a study of the entire mount note that a second, the cervical flexure,
has appeared in the head. Note that the tail fold is well formed. Note
the position of the embryo on the blastoderm. Determine if the amnion is
completely closed. Note the olfactory pits on the ventral surface of the
head, a short distance in front of the optic stalks. Note the
telencephalon, a rudiment of the cerebral hemispheres and an extension
of the primary forebrain. It is bilobed anteriorly. The optic stalks are
attached to the floor near the anterior end of the thalamencephalon.
Note the infundibular region, which is the depressed region behind the
optic stalks. In the roof of the thalamencephalon there is a short
diverticulum, the epiphysis. The mesencephalon, or midbrain, forms the
apex of the cranial flexure, and is united to the hindbrain by a narrow
isthmus. The metencephalon, or rudimentary cerebellum, appears as a
thick portion on the most anterior division of the hindbrain. The rest
of the hindbrain is provided with a transparent roof and constitutes the
myelencephalon, or the rudimentary medulla oblongata. Observe the inner
and the outer wall of the optic cup, the lens, the choroid fissure, and
the posterior, or vitreous, chamber.

Note the form of the otocyst, or auditory sac. Note above which visceral
arch it lies. Note the number of visceral clefts. The visceral arches
are formed by the thickening of the walls of the bounding clefts. The
visceral arches are as follows: the first is the mandibular, or
hyomandibular, arch, which is in front of the first cleft. From this
there is developed the lower jaw. Note if there is a maxillary process
arising from the dorsal angle of the arch. The second arch is the hyoid
arch, which is located behind the first cleft. Then follow in order the
third, the fourth, and the fifth visceral arches. Note above the
mandibular arch the rudimentary trigeminal ganglion, and above the hyoid
arch the rudimentary acoustico-facialis. The latter is in contact with
the anterior walls of the auditory sac. The rudimentary
glosso-pharyngeal ganglion is noted above the third visceral arch. The
vagus, or pneumogastric, ganglion is located above the fourth and the
fifth. Note the form and the position of the heart. Note the anterior
and the posterior limb rudiment in the trunk.

In a study of the sections it is found that cuts transverse to the trunk
pass about horizontally through the forebrain. At this age the following
sections of the embryo should be studied:

First, through the hindbrain, at which level will be noted the auditory
sacs, the neuromeres, the trigeminal, the acoustico-facialis, and the
glosso-pharyngeal and the vagus ganglion.

Second, through the upper part of the pharynx, at which level will be
observed the midbrain, the hindbrain, the visceral pouches, the nerves,
and the blood-vessels.

Third, through the choroid fissure of the optic cups. Note the parts of
the eye, and, on the other side of the section, the heart.

Fourth, a study of a section through the olfactory pits.

Fifth, a study of a section through the pancreatic and the hepatic
diverticula.

Sixth, a study at the beginning of the allantois through the hind-gut.

At this age it is of interest to study the systems of organs. Observe
the manner in which the splanchno-pleure folds to form the walls of the
intestine. Note the commencement of the mesentery. Note that the
foremost part of the alimentary tract is formed from the stomodeal
invagination of the ectoderm. The hypophysis is formed from a dorsal
outgrowth of this. Note its relation to the brain.

The following structures are formed from outgrowths of the ectoderm at
this stage:

First, the visceral pouches.

Second, the median rudiment of the thyroid. This is an outgrowth from
the pharynx between the two hyoid arches.

Third, the rudimentary lungs, which develop in a pair from a median
ventral diverticulum of the alimentary tract, just behind the last
visceral pouch. The esophagus is just posterior to this. The esophagus,
very short at this stage, is continuous with a slightly wider part that
develops into the stomach.

Fourth, the first liver diverticulum, and, at a short distance posterior
to this, the second liver diverticulum.

Fifth, the pancreas is at a point where the intestine opens ventrally.
It first appears as a slight thickening of the dorsal angle of the
intestine.

Sixth, the ventral wall of the hind-gut forms a wide evagination.

Seventh, the beginning of the allantois.

After the whole series of transverse sections have been studied and
drawn, construct a longitudinal section of the fetus, including a
reconstruction of the alimentary tract.

At this stage the =heart= is a simple tube. The following divisions are
distinctly visible: the auricular portion, the ventricular portion, the
sinus venosus, and the bulbus arteriosus. The union of the two ductus
Cuvieri and the ductus venosus form the sinus venosus. The two ductus
Cuvieri are formed by the union of the anterior and the posterior
cardinal veins. The ductus venosus is formed by the union of the small
right and the large left vitelline vein. These latter veins return the
blood from the yolk sac. The sinus venosus empties into the single
auricle above which it is located. The single auricle is later divided
into two chambers, the right and the left auricle. At this stage it is
widest in the lateral direction. The auricle empties directly into the
ventricle. The ventricle lies ventrally and behind the auricle. This
location is due to the bending of the heart at this stage of
development. Its hindmost portion forms the future apex of the heart. If
the series of sections be studied from the posterior forward, the
ventricle will be first to appear in the sections. Just beneath the
auricular portion of the heart there is the bulbus arteriosus. The
bulbus arteriosus soon divides into a number of aortic arches. There is
an ascending pair in each of the visceral arches. The dorsal aorta is
formed by the union of the aortic arches above the visceral arches. The
aortic arches are first continued a short distance forward as the
carotid arteries. The dorsal, or posterior, aorta passes backward under
the notochord. The dorsal aorta divides into two parallel aortæ which
give off on each side the vitelline arteries. Note other branches of
this aorta.

The veins at this stage consist of the anterior and posterior cardinal,
the ductus venosus, the ductus Cuvieri, and the vitelline veins.

Make drawing of the circulatory system after a completion of the study
of the series of sections.

Make a study of the =nervous system= according to hints already given.

The dorsal and the ventral roots of the spinal nerves are given off
separately, and secondarily unite. From the neuroblasts of the cord
there are at regular intervals outgrowths representing the ventral
roots. From the neural crest there develop segmental collections of
neuroblasts which form the spinal ganglia, from which the dorsal spinal
nerve roots develop. In fact this developmental stage can be observed in
embryos only forty-eight hours old, first appearing as a line of cells
springing on each side from the angle between the neural canal tube and
the external epiblast. In the section from the embryo seventy-two hours
old there are observed the rudiments of the development of these spinal
nerves. Four primary ganglia develop in the neural crest of the head.
These ganglia are as follows: the acoustico-facialis ganglia, which is
located over the hyoid arch; the ganglia of the trigeminus, which is
located over the mandibular arch; the ganglia of the glosso-pharyngeus,
which is located over the third visceral arch; and the ganglia of the
vagus, which is located over the third and the fourth visceral cleft.

In this stage of development the trigeminal and the acoustico-facialis
are clearly visible.

On each side and dorsal to the aorta is noted the Wolffian body, or
mesonephros. The Wolffian body (Fig. 82, _E_) consists of a series of
tubules imbedded in the mesenchyme. The openings into the Wolffian duct
lie just beneath the cardinal vein.

In a study of the =Wolffian duct= determine just how far anteriorly and
how far posteriorly it extends. Note whether it empties into the cloaca.

Each tube beginning in a blind extremity is later dilated. It has a thin
wall, and is situated near the median portion of the Wolffian body. The
tubule proper passing transversely, opens into the duct. The upper wall
of the thin walled part is invaginated by a mass of mesenchyme that
receives a small vessel from the dorsal aorta. The Malpighian corpuscle,
consisting of a glomerule and Bowman’s capsule, is thus established. In
the study of the four days old chick note the further development of
these parts.

In a study of a chick four days, or ninety-six hours old, note to what
extent the yolk is covered by the blastoderm. It will be noted that the
embryo lies in the extra-embryonic cavity. This cavity is bounded above
by the chorion and below by the splanchno-pleure. In removing the amnion
from the embryo, note the relation to the somatic umbilicus. Note the
relation of the splanchnic umbilicus to the splanchno-pleure. What
relation has the allantois to the above?

In examining the head, locate the cerebral hemispheres, and note their
development. Locate the pineal gland. Note changes in the olfactory pit
and the eye. Locate the lens and the choroid fissure. Note that the
maxillary process of the mandibular arch lies beneath the eye and behind
the olfactory pits. Note the otocyst and the relations of the other
arches to the above structures.

In a study of the =trunk=, note the tail, the allantois, Wolffian
ridges, the heart, and the condition and the position of the rudimentary
limbs.

Make drawing of embryo from the side view. Carefully cut off the head
immediately behind the last visceral arch, and study and draw the
structures observed on the ventral side. Note the maxillary processes,
the mandibular and the hyoid arch, the nasal pits, and the fronto-nasal
process, which is just beginning its development.

In a study of transverse sections observe from your drawing at what
level the section is made. Study and draw a section made through the
region of the anterior limbs. Note the spinal ganglion, the muscle
plate, or myotome, the condensation of mesenchyme around the notochord,
the pancreas, the liver, and the intestine; and note the distribution of
the mesenchyme. Note the ventral roots of the spinal nerves, and the
neuroblasts in the spinal cord.

In sectioning the embryo from before backward, the first sections will
pass horizontally through the hindbrain and the midbrain region. Note
the parts, including the auditory vesicle. In the first series of
sections also locate the ganglia of the pneumogastric, or vagus, the
acoustico-facialis, the trigeminus, and the glosso-pharyngeal nerves.
Note the notochord and the cardinal veins. After the disappearance of
the ear, we observe the midbrain, which, is located at one end of the
section, and the cord at the other end. The region between lies just
above the pharynx. In the following series study the visceral arches.
Note the third pair of cranial, or motor ocular, nerves. This latter
nerve springs from the floor of the midbrain. From the ventral
prolongation of the floor of the thalamencephalon there arises the
infundibulum. The hypophysis is located just beneath the infundibulum.
At this stage the hypophysis appears as a tube to empty into the mouth.
This is an ingrowth of the oral epithelium.

In a study of a section through the center of the eye we should observe
the lens and optic stalk. This is in the region of the optic chiasm.
Note the choroid fissure and the pineal gland, the latter appearing just
beyond the eyes. Just forward lies the telencephalon, or rudiments of
the cerebral hemispheres.

In a study of the =alimentary tract= we note that the mouth is bounded
by the mandibular arches. Note the maxillary processes, and the ventral
surface of the head. A finger-like diverticulum, extending from the roof
of the ruptured double membrane, formerly separating the pharynx from
the arches, forms the hypophysis. The great development of the visceral
pouches makes the pharynx rather complex. In studying sections
horizontally through the pharyngeal region note the various visceral
arches and pouches. Note the arteries of the thyroid diverticulum.

In the series note the changed development of the lung rudiments, the
glottis, the esophagus, the trachea, and the bronchi. The bronchi appear
in pairs. Note that the liver has assumed proportions, and that it
surrounds the common trunk of the vitelline veins, which it divides into
two parts. The sinus venosus lies close to the heart. The ductus venosus
is also surrounded by the liver. Above the tip of the ventricle we note
a dilatation which represents the stomach. The hepatic, or bile duct is
located immediately behind the stomach. This duct is formed by the
fusion of the right and the left duct. Locate, draw, and describe the
pancreas; trace the intestine; locate the splanchnic umbilicus, or yolk
stalk; locate the allantois stalk, and trace its connection with the
hind-gut.

In the series, locate and study the Wolffian ducts, the beginning of the
Müllerian duct, the embryonic kidney, or mesonephros, the permanent
kidney, or metanephros. The urino-genital ridge is made up of all the
above except the last named. The urino-genital ridge forms a rounded
projection on each side of the mesentery into the dorsal angles of the
body cavity.

The Wolffian ducts empty into the cloaca. There are two ducts which may
be traced far forward, and which are found to extend backward along the
lateral margin of the ridge to the cloaca. Along the greater part of
their length we note tubules emptying into them.

Beginning near the anterior end of the urino-genital ridge, we note that
the Müllerian ducts arise from a thickened line of epithelium. The
greater part of the ridge is formed by the mesonephros. This is made up
of a series of tubules in each of which we may distinguish two parts as
follows: a tuft of capillaries from the aorta forming the glomerules,
surrounded by a thin walled invaginated capsule, making up the
Malpighian corpuscle; and the tubules proper. The tubules lead from the
corpuscles, or glomerules, to the Wolffian duct.

The germinal epithelium constitutes the essential portions of the gonad,
or ovary, or testis. The germinal epithelium arises from a thickening of
the peritoneum of the median wall of the ridge. The gonad is found near
the anterior end of the ridge. At about this age of the embryo there
should appear the primitive ovary or testis. Near the posterior
termination of the Wolffian duct and from the dorsal diverticulum there
arises the ureter, or metanephros duct.

In these series there should be studied the heart and circulation, which
will be found similar to the sections from the embryo seventy-two hours
old.

Work out a summary of the relations of the allantois and the yolk stalk
to the intestines; the relations of the Wolffian ducts to the
intestines; the origin of the ureters from the Wolffian ducts; the
relations of the lungs, the liver, and the thyroid gland; the relations
of the blood-vessels; a study of the muscle plates; the relations of
epiphysis, hypophysis, infundibulum, mouth, and pharynx; the relations
of the vagus, or pneumogastric, trifacial, acoustico-facialis, and
glosso-pharyngeal nerves to the visceral arches.

In addition to the study of embryos at the end of each of the first four
days of incubation, a study should be made of preserved museum specimens
each of which represents the development of a day up to and including
the twenty-first day.


                   THE DERIVATIVES OF THE GERM-LAYERS

From the three primary germ-layers are developed the various tissues and
organs of the body by metamorphoses which may be referred to the two
fundamental processes of specialization, or the adaptation of structure
to function, and of unequal growth, which latter results in the
formation of folds, ridges, and constrictions.

From the ectoderm are produced:

The epidermis and its appendages, including the nails, the epithelium in
connection to the feathers and the feathers.

The infoldings of the epidermis, including the epithelium of the mouth,
epithelium of the salivary glands and the anterior lobe of the pituitary
body, or hypophysis.

The epithelium of the nasal tract with its glands and communicating
cavities.

The epithelium lining the external auditory canal, including the outer
stratum of the membrana tympani.

The lining of the anus.

The epithelium of the conjunctiva and of the anterior part of the
cornea, the crystalline lens.

The spinal cord, the brain with its outgrowths, including the optic
nerve, the retina, and the posterior lobe of the pituitary body.

The epithelium of the inner ear.

From the entoderm are produced:

The epithelium of the respiratory tract.

The epithelium of the digestive tract, from the back part of the pharynx
to the anus, including its associated glands, the liver, and the
pancreas.

The epithelial parts of the middle ear and of the eustachian tube.

The epithelium of the thymus and the thyroid bodies.

From the mesoderm are developed:

Connective tissue in all its modified forms, such as bone, cartilage,
lymph, blood, fibrous and areolar tissue.

Muscle tissue.

All endothelial cells, as of joint-cavities, bursal sacs, lymph sacs,
blood-vessels, pericardium, and endocardium, pleura, and peritoneum.

The spleen.

The kidneys and ureters.

The testicles and the system of excretory ducts.

The ovary and oviduct.


                  PREPARATION OF STRUCTURES FOR STUDY

It is hoped that the following suggestions will be helpful in the
laboratory work.

=Directions for Dissecting Muscles.=—The muscles that are brought into
great play in movements of the bird’s limbs are dark carmine in color,
while those which are not brought greatly into use are pale or white in
color.

The tendons are made up of white fibrous connective tissue, are very
dense, and pearly white in color.

In securing a bird for dissection of muscles it is best to select one in
rather poor flesh, as the fat is annoying. The bird may be chloroformed
or killed in a bell jar by aid of illuminating gas. After the bird is
dead pluck all the feathers and immerse it in a 10 per cent. solution of
formaldehyde or of 80 per cent. alcohol. It is best to puncture the
abdominal wall so that the fluid may at once fill the abdominal cavity
and more readily gain access to the chest cavity; and to puncture the
skin at various points so that the liquid may more quickly become
disseminated among the muscular structures. Post-mortem changes quickly
take place if these precautions are not taken. The liquid surrounding
the carcass should be at least twice the quantity of the bulk of the
carcass.

The first dissection should be to lay bare the dermal muscles. The
dermal muscles are of two kinds, true dermal and dermo-osseous. The
dermal muscles have their origin and insertion in the skin, and control
the movements of the different groups of feathers. The dermo-osseous
have their origin on some part of the skeleton, and insert to the
integuments.

The dermal muscles vary with the characteristics of the bird, we do not
find all the known dermal muscles in any one specimen. A cock of the
Cornish breed will show these muscles best developed. Birds possess an
enormous system of minute muscles divided up into an infinite number of
fasciculi, to act harmoniously upon the feather quills and to agitate
collectively the plumage. By the aid of a low-power lens the action of
the feather muscles in the large quill butts of the wing or the tail may
be studied.

The muscles may be studied in groups as outlined in the text. Make an
incision through the skin down to the bone on the superior part of the
head, parallel and close to the base of the upper mandible, and
extending completely across. From the outer end of this make an incision
backward and down to the skull and posteriorly. The muscles of the upper
part of the neck will then be exposed. The straight incision should
extend to about a half inch on the inside of the upper eyelid of the
same side. Reflect the flap of skin from the top of the skull, and
carefully examine the under side of it in the median line, where it
overlies the frontal region. The dermo-frontalis will be observed if it
be present. In many birds, especially in females, it may not be
discernible, and may be considered absent. To expose the circumconcha
make an incision completely around the ear; then carefully dissect to
the ear base. A dermal circular muscle should be observed. To expose the
dermo-temporalis extend the longitudinal incision down the back of the
neck to a point between the clavicular heads, carrying it just through
the skin and about one-fourth of an inch to the side of the median line.
Remove the skin from the throat and the anterior portion of the chest.
Lay open the alar and parapatagial duplicatures of the skin. This
exposes a number of dermal muscles. The dermo-temporalis is now observed
to extend from a small depression just above and anterior to the
temporal fossa. It makes slight attachments to the temporal muscle,
which it covers, and extends backward as a thin ribbon-shaped muscle,
the fibers blending with those of the cleido-trachealis, and becomes
lost upon the skin in front and opposite the shoulder-joint. At times
its fibers blend with those of the dermo-tensor patagii.

As the musculature of the fowl is loosely arranged, the rest of the
dissection is easily done if care be exercised.

The ligaments may be dissected after the completion of the study of
muscles, using the same subject or, a two pound broiler be prepared by
killing in the gas chamber, plucking the feathers and parboiling just
till the flesh becomes tender and is easily removed, it will be observed
that all structures can be removed from the points exposing the
ligaments distinctly. The ligaments appear swollen and more easily
observed for study.

=Directions for the Study of the Viscera.=—Carefully remove the right
and the left abdominal and thoracic walls, allowing a strip of tissue to
remain in the median line to hold the organs in their normal position.
To open these cavities it is necessary to use the bone saw and the
scalpel. The organs may now be studied from each side. To make a
longitudinal section through the median line, select a small bird, one
weighing not more than 2 pounds, kill, and preserve in a 10 per cent.
solution of formaldehyde for three days. Then with a sharp, thin,
long-bladed knife make an incision at one sweep through the median line
of the body down to the back bone, and with the bone saw section through
the vertebræ. If it is difficult to cut through the breast-bone, saw
through before making the incision. In small birds the entire cut may be
made without the aid of the saw.

=Directions for the Study of Arteries.=—Arteries should be injected.
Veins are usually more or less filled with blood so that the tracing of
these is not so difficult as the tracing of uninjected arteries. Nerves
are white and no difficulty is usually encountered in tracing them.

The courses of arteries, veins, and nerves are side by side, and many of
them, as in mammals, are arranged in the order of veins, arteries,
nerves, the veins being in front.

The injection apparatus consists of the following parts: air-compression
chamber, to which is attached a pressure pump. A manometer made of glass
tubing 6 millimeters in diameter, inside measurement. This tube is
partly filled with mercury, and a scale in centimeters is made from the
top of the right-hand tube (Fig. 84, No. 8). This ruling, or gauge,
should be about 15 centimeters long. Extending from the right extremity
of the U-tube is a small rubber tubing which is attached to the chamber
containing the injection fluid; and extending from the inferior part of
this chamber is another tubing which has the injection needle attached
to the free end.

The injection should be done under 120 millimeters pressure. The stop
cock of the pressure chamber is released sufficiently to raise the
mercury in the U-tube six centimeters, which multiplied by 2, the amount
of work required to raise two columns, makes 120 millimeters pressure.
If this pressure be maintained, all vessels should be injected without
rupture. The same process may be used in injecting the air cells through
the trachea.

The injecting material may consist of one part finely sifted plaster of
Paris, four parts water, and sufficient gentian violet to make a violet
color. For the coloring, red aniline may be used in preparing this
material. The dye should be dissolved in the water to be used in making
the injection liquid. Caution must be used and the work rapidly done, as
the plaster soon sets, or becomes solid, in the needle or in the tubing.
A small cannula should be used, since the endothelial lining of the
arteries are easily injured and difficulty may thus be created.

Select for arterial dissection an old cock, as in a bird of this kind
the arteries are larger and the difficulties are reduced. Select for
bleeding and injection the ischiadic artery in the thigh region. With
the sharp point of the thin blade of a knife make an incision lengthwise
of the artery being careful not to strip back the endothelial lining of
the artery. Allow as much of the blood as will escape before injecting;
in fact, the arteries should be thoroughly emptied, so that there is no
longer danger of a clot’s plugging some vessel and thus preventing its
filling. Since the blood of most birds coagulates in about thirty
seconds, this work must be done rapidly, care being exercised to keep
the flow running as long as possible. After bleeding is completed,
insert the cannula and tie the vessel tightly around the cannula to
prevent the escape of the injecting fluid. See that all connections are
sufficiently tight to prevent the escape of liquid under pressure. After
the injection is completed, remove the cannula and tie the artery with a
small twine, preferably cotton. Quickly remove all injecting fluid from
the needle, the tubing, and the injecting chamber.

During the operation of bleeding the cock may be chloroformed, care
being taken not to administer chloroform to kill him; for it is
necessary to maintain life as long as possible so that the heart may be
kept beating and all blood possible drained from the arteries. After the
injection is completed the bird may be plucked and immersed in the
preservative fluid in the same manner as in the preparation for
dissection for muscles.

The arteries, the veins, and the nerves may now be dissected and studied
in relation to one another and in relation to the muscles, the bones,
and other structures. The skin should not be removed from the shanks
till it is desired to dissect these parts, as the tissues quickly dry
out. In fact, the tendons of the shanks and toes can best be dissected
while the specimen is fresh.

=A Study of the Structure of Bones.=—Longitudinal and transverse
sections of old bone may be made by making thin longitudinal and
transverse sections with the bone saw, and then by making them very thin
with a fine three-cornered file. Examining under the low power
microscope, we note the lacunæ, the canaliculi, and the Haversian
system.

Similar sections in green bone may be studied if prepared as follows.
Secure specimen of bone just removed from a fowl and place it for three
days in a 10 per cent. aqueous solution of hydrochloric acid. Test by
puncturing with a needle, and, if all the mineral salts are removed,
place in a water bath and wash for four hours. Pass it through the
fluids usually employed in preparing specimens for sectioning with the
microtome. Stain as sections of other tissue for microscopic study. See
the description below. If the ends of the bone be included, it will
enable the student to study not only compact bone but also cancellated
bone and articular, or hyaline cartilage, and in some of the bones, as
the femur, the red marrow.

=Special Technic for the Dissection of Cranial and Spinal Nerves.=—It is
rather difficult to dissect the cranial and spinal nerves of the fowl,
owing to the fact that the structures are very small. The bone is rather
hard and the nerve tissue so delicate that great skill must be attained
to achieve any degree of success.

A simple technic has been developed as follows: Place the head and neck,
or other structures of the spinal column in a 10 per cent. aqueous
solution of hydrochloric acid for three or more days, the time depending
on the size of the specimen and the amount of soft structures
surrounding it. This solution removes all the calcium salts from the
bone and makes the removal of the bony structures a less difficult task.

=Directions for the Study of Soft Structures.=—Secure a specimen of the
tissue to be studied—lung, muscle, intestine, liver, pancreas—from a
normal fowl just killed. The specimen should be not more than ½ inch
square. After first hardening three days in 10 per cent. formaldehyde.
Pass through the following fluids:

 1. Alcohol, 95 per cent.                                        24 hours
 2. Alcohol, absolute                                            24 hours
 3. Alcohol and ether, equal parts                               24 hours
 4. 1 per cent. celloidin                                        24 hours
 5. 2 per cent. celloidin                                        24 hours
 6. 4 per cent. celloidin                                        24 hours
 7. 6 per cent. celloidin                                        24 hours
 8. 10 per cent. celloidin                                       24 hours
 9. Place on block, and as soon as solid, place in 80 per cent. alcohol
     until ready to section. Histoloid or parlodion will take the place
     of celloidin.

In placing specimen on the block be careful that the specimen lies
conveniently for cutting the sections in the right direction. As soon as
the surface has hardened a little, add a few drops of thick celloidin,
and repeat until there is a good body of celloidin. Allow to stand until
the tissues are quite firmly fastened to the block, but not long enough
to permit shrinking. Then place in 80 per cent. alcohol until the
specimen is perfectly firm, 12 or more hours, before cutting.

All tissues, cut sections, and mounted blocks are to be placed in 80 per
cent. alcohol. As containers for this purpose shell vials will be most
handy.

Cut the sections with the microtome as thin as possible, the thinner the
better. The following process of staining will make the nucleus blue and
the cytoplasm reddish.

  1. Float section in a tumbler of tap water.

  2. Place section on slide, and immerse in hematoxylon for five to ten
       minutes.

  3. Immerse in acid alcohol from two to five seconds.

  5. Place on slide, and immerse in eosin from one-half to three
       minutes.

  6. Wash thoroughly in alcohol.

  7. Clarify in oil of cloves, oil of cedar, or beechwood creosote, ten
       minutes.

  8. Mount in balsam.

  9. Label and study.

Delafield’s hematoxylon is prepared as follows:

          Hematoxylon crystals                        4 grams
          Alcohol, 95 per cent                        25 c.c.
          Saturated aqueous solution of ammonia alum 400 c.c.

Add the hematoxylon dissolved in the alcohol to the alum solution, and
expose in an unstoppered bottle to the light and air for three or four
days. Filter and add:

                     Glycerin              100 c.c.
                     Alcohol, 95 per cent. 100 c.c.

Allow the solution to stand in the light until the color is sufficiently
dark; then filter, and keep in a tightly stoppered bottle. The solution
keeps well and is extremely powerful. So long as it is good the solution
has a purplish tinge. If time permits, it would be wise to combine the
alum, the hematoxylin, and the water, and to ripen the solution for two
or three weeks before adding the other ingredients, which have a
tendency to prevent oxidation.

The acid alcohol is made as follows:

                       Absolute alcohol  70 c.c.
                       Distilled water   30 c.c.
                       Mix.

                       Above solution    99 c.c.
                       Hydrochloric acid  1 c.c.

Eosin is sold in two forms, that soluble in water and that soluble in
alcohol. The eosin soluble in water is preferred, because with it a
greater degree of diffusion in stain can be obtained.

Keep on hand a saturated aqueous solution and dilute with water as
needed. The strength of the solution to be used varies somewhat with the
tissue and the reagent in which it is to be fixed; but usually the
strength should be between ⅒ and ½ per cent. when eosin is used after
hematoxylin. The diluted solutions should contain 25 per cent. of
alcohol, otherwise they will not keep well. When eosin is used before an
aniline dye, such as methylene blue, a 5 per cent. or even a saturated
solution should be used.

=To Stain Sections of Liver for the Study of Kupffer Cells.=—To bring
out this reaction Keys suggests the following technic:

Fix small blocks of the fresh tissue of spleen or liver for eighteen to
twenty-four hours in Müller’s fluid plus 5 per cent. mercuric sublimate.
Imbed in paraffin and section to 4 microns. Fix sections to slide, and
stain twenty to forty minutes with acid carmine. Wash, and transfer to
equal parts of a 2 per cent. aqueous solution of potassium ferrocyanid
and of a 2 per cent. aqueous solution of hydrochloric acid. Remove after
three to ten minutes, wash in distilled water, and pass quickly through
a 0.5 per cent. aqueous erythrosin solution. Dehydrate in alcohol,
clarify in xylol, and mount in Canada balsam.

=To Prepare Anatomical Specimens for a Museum.=—The Keiserling method
gives the best results, since by this method the tissues retain their
normal color. The three steps are as follows:

1. Place the specimen in the following solution and leave from one to
seven days, the length of time depending upon the size of the specimen.

                      Formalin           200 c.c.
                      Potassium acetate   30 grams
                      Potassium nitrate   15 grams
                      Water             1000 c.c.

2. Pass the specimen through each of the following solutions, leaving it
in each twenty-four hours or until the normal color is obtained. The
specimen should be removed from alcohol as soon as color is attained. If
it is left in the alcohol too long it will again lose some of its color.

                         Alcohol  40 per cent.
                         Alcohol  60 per cent.
                         Alcohol  80 per cent.
                         Alcohol full strength

3. Place the specimen in the following permanent solution, label, and
place in museum.

                       Glycerin           40 c.c.
                       Potassium acetate 40 grams
                       Distilled water   400 c.c.

A small piece of thymol must be placed on the top of the liquid in each
jar, or mold will develop and spoil the specimen.

=To Make Specimens Transparent.=—Specimens may be rendered transparent
by the method of Spalteholz.

The steps are essentially as follows:

I. Preparation of the fresh tissue. If any parts are to be made
conspicuous, as blood-vessels, or the lymphatic system, they must be
injected with an insoluble, unbleachable substance. Spalteholz
recommended carmine or methylene blue, and carbon. I have found Higgin’s
ordinary black carbon ink excellent for this purpose. The system or
systems are injected with this substance while the tissue is perfectly
fresh.

II. Fixation. The tissues are fixed preferably in 10 per cent. formalin.
The length of time for fixation depends on the size of the tissue. In
formalin it requires from eight hours upward to fix completely.

III. Rinsing. Running tap water for five or ten minutes accomplishes the
rinsing. If it is impracticable to pass directly into the bleaching
fluid, the tissues may be kept temporarily in 60 per cent. or 70 per
cent. alcohol. They should then be rinsed again thoroughly in water when
ready to bleach.

IV. Bleaching. The bleaching fluid used is hydrogen peroxid to which
ammonia is added until a white precipitate forms. The proportion is
approximately two parts of peroxid and one of ammonia. The material is
bleached until all the color is removed and the tissue looks perfectly
clear or slightly opaque. It may be quite transparent as the protein
coagulate is somewhat white, but all yellow or reddish color should be
bleached away.

V. Washing. Rinse thoroughly in running tap water or through several
changes of water until the odor of ammonia is quite gone.

VI. Dehydration. Pass gradually through alcohol solutions, 30 per cent.,
50 per cent., 60 per cent., 70 per cent., 80 per cent., 95 per cent.,
and last through absolute alcohol. The time required for dehydration
will vary with the size of the material, but in either 95 per cent.
solution or in absolute alcohol the tissue should remain until well
hardened, twenty-four hours or more. Dehydration is completed by passing
from absolute alcohol, to a fluid one-half absolute alcohol and one-half
benzol; thence for a few days to pure benzol.

VII. Clarifying. From benzol the material is finally clarified in
winter-green oil or any other standard clearer, and put up in its final
position in the museum jar.

In commenting on this method Dr. A. F. Contant says: “I have found this
to work very successfully in the injection of the lymphatics of the
human skin, which, as you know, is a rather delicate injection and has
been difficult of demonstration by other methods. With this method,
however, I have prepared whole portions, as the side of the face, the
leg, etc., of small animals and embryos which show clearly the whole
course of the lymphatic vessels and nodes, in situ, and their relations
to surrounding parts.”


                EQUIPMENT FOR THE DISSECTION LABORATORY

Figure 84 illustrates some essential equipment for the dissection
laboratory. The equipment should consist of a pump, No. 1, which forces
air through the rubber tube, No. 2, into the pressure tank, No. 4, which
is guarded by the valve at No. 3. A dial, No. 5, indicates the pressure
of the air within the tank. The air as needed is released through an
outlet valve. The air now passes through the rubber tube, No. 6, into
the left arm of the manometer at No. 7. The manometer is simply a glass
tubing filled with mercury to the point indicated at No. 7. By the side
of the opposite arm there is made a scale graduated in centimeters. The
tube at No. 9 being attached to the Y-tube, conveys air under the same
pressure into the injection chamber as that supporting the column of
mercury of the manometer. It is necessary to have a pinch cock, as
indicated at No. 11, to control the liquid within the tube. No. 12
illustrates the tube in the end of which, No. 13, there is inserted a
trocar which is introduced into the artery and tightly tied with a cord.

[Illustration:

  FIG. 84.—Photograph showing injection apparatus, dissection
    instruments, dissection pan and death chamber.

  1, Pump. 2, Rubber tube leading from pump to compression chamber. 3,
    Stop cock. 4, Compression air tank. 5, Pressure indicator. 6, Rubber
    tube leading from pressure tank to manometer. 7, Top of mercury in
    manometer tube. 8, Open end of glass tube showing scale in
    centimeters. 9, Tube leading from 4 to injection chamber. 10,
    Injection chamber containing injection fluid. 11, Pinch cock on
    rubber tube connecting injection chamber with injection canula. 12,
    The tube. 13, Injection canula. 14, A metal dissection tray. 15,
    Death chamber. 16, Base of same. 17, Rubber tube connecting gas cock
    with death chamber. 18, Bone saw. 19, Bone cutter. 20, Scapula. 21,
    Tenaculum. 22, Forceps. 23, Straight scissors. 24, Small pair of
    curved scissors.
]

A convenient dissection tray may be made from galvanized iron. It should
be 16 inches square and about 1 inch deep (Fig. 84, No. 14).

A death chamber is made by using a bell jar 12 inches in diameter at the
bottom. This is used on a perfectly smooth board 16 inches square.
Through the center of this board is inserted a glass tube ⅜ inch in
diameter. To this glass tube is attached a rubber tube the other end of
which is attached to a gas jet.

The instruments needed in dissecting are illustrated in Fig. 84. No. 18
is a bone saw; No. 20 is a scalpel; No. 21 is a tenaculum; No. 22 is a
pair of forceps; No. 23 is a pair of straight scissors; and No. 24 is a
small pair of curved scissors.




                              BIBLIOGRAPHY


  BAUM AND ELLENBERGER, Handbuch der Vergleichenden Anatomie, Berlin,
  1912.

  BARROWS, H. R., _Me. E. S. Bull._ 232, pp. 16, plates 6, 1914.

  BRADLEY, O. CHARNOCK, The Structure of the Fowl, pp. 146,
  illustrations 73.

  CHAVEAU, A., Comparative Anatomy of Domestic Animals, New York, 1893.

  CURTIS, M. R., Ligaments of the Oviduct of the Fowl, _Me. E. S. Bull._
  206, 1910.

  DUVAL, ——, Atlas of Embryology.

  FOSTER AND BALFOUR, Elements of Embryology.

  GADOW, H., AND SELENKA, E., Vögel. I. Anatomischer Theil (Dr. H. G.
  Bronn’s Klassen und Ordnungen des Thier-Reichs. Sechester Band, Vierte
  Ahtheiburg), Leipsig, 1891.

  GRAY, HENRY, Anatomy Descriptive and Surgical, New York, 1908.

  HEISLER, J. C., Embryology, Philadelphia, 1901.

  KAUPP, B. F., Male Reproductive Organs of the Fowl, _Am. Jr. Vet.
  Med._, vol. x, 11, 2.

  KAUPP, B. F., Female Reproductive Organs of the Fowl, _Am. Vet. Rev._,
  vol. 49, 11, 4.

  Leisering Atlas of Anatomy, edited by W. ELLENBERGER, translated by A.
  T. PETERS, Chicago, 1905.

  LILLIE, F. R., Embryology of the Chick, Chicago, 1906.

  OWEN, R., Comparative Anatomy and Physiology of Vertebrates, London,
  1866.

  SCHMEISSER, H. C., A Study of the Blood of Fowls, Johns Hopkins
  Hospital, 1915.

  SHUFELDT, R. W., Myology of the Raven, pp. 318, illustrations 76,
  London, 1890.

  Strangeways’ Veterinary Anatomy, edited by I. VAUGHAN, Edinburgh,
  1892.

  SURFACE, F. M., Histology of the Oviduct of the Fowl, _Me. E. S.
  Bull._, 206, 1912.




                                 INDEX


 Abdominal air-sac, 202
   cavity, 156

 Abducens nerve, 270

 Abductor minimi digiti muscle, 110

 Accessorius spinalis nerve, 274

 Accessory organs of digestion, 152

 Acetabulum, 48

 Achillis tendon, 69

 Acoustic lamina, 323
   nerve, 306
   vesicle, 322

 Adductor longus muscle, 117
   magnus muscle, 117

 Adrenal gland, 191

 Adventitia, 201

 Afferent nerves, 300

 Air-sacs, 199, 325
   abdominal, 202
   anterior diaphragmatic, 202
     thoracic, 200
   cervical, 201
   femoral extensions, 203
   humeral extension, 200
   posterior diaphragmatic, 202
   subpectoral prolongation, 200
   subscapular prolongations, 200
   suprarenal extensions, 203

 Alæ cinereæ, 291
   orbitale, 28
   temporales, 29

 Albumin, 180
   portion of oviduct secreting, 185

 Allantois, 321

 Alula, 311

 Alveolar glands, 141
   nerve, 270

 Amnion, 320, 327

 Ampullæ, 306

 Ampullar dilatations, 322

 Anapophyseal ridge, 38

 Anatomic specimen, preparation of, 349

 Anconeus muscle, 107

 Angiology, 206

 Angular glands, 141
   groove, 52

 Annular ligament, 58

 Annulus fibrosus, 58

 Anterior coraco-brachialis nerve, 284
   diaphragmatic air-sac, 202
   fossa, 25
   thoracic nerve, 284

 Aortic arch, 325
   bulb, 324

 Aponeurosis, 59

 Apparatus, circulatory, 206
   digestorius, 135
   respiratory, 193
   uro-genitalis, 169
   vocal, 195

 Appendages, structure of, 309

 Appendico-costales muscle, 99

 Appendicular skeleton, 13

 Apteria, 34

 Aqueduct of Sylvius, 268, 289

 Arachnoid, 288, 289

 Arbor vitæ, 291

 Arch, hemal, 38
   scapular, 40

 Area opaca, 332
   pellucida, 332
   vasculosa, 332

 Arteria cerebri profunda, 217

 Artery or arteries, 209, 325
   acromial, 222
   anterior circumflex humeral, 222
     vertebral, 221
   aorta, 211
   auricular, 220
   axillary, 222
   basilar, 217
   brachialis, 222
   brachio-cephalic sinister, 212
   bronchialis, 215
   carotid trunk, 215
   carotis cerebralis, 215
     communis, 215
     externa, 215
   celiac axis, 226
   cerebral, 217
   cerebri profunda, 217
   cervicalis ascendens, 221
   circumflex femoris, 228
   clavicular, 222
   coccygeal laterales, 232
   collateralis radialis, 223
   common aorta, 211
   coronary, 209
   crural, 228
   esophageal, 224
   ethmoidal, 218
   ethmoidales externa, 218
   external facial, 220
     thoracic, 222
   facial, 220
   femoral 228
   hemorrhoidalis intima, 232
   hepatica dextra, 227
   hyoid, 218
   iliac, 229
   inferior cerebellar, 217
     esophageal, 215
     thoracic, 222
   intercostal, 224
   internal alveolar, 220
     ethmoid, 218
     facial, 220
     mammary, 222
     maxillary, 220
     ophthalmic, 217
     pelvic, 228
     thoracic, 222
   lacrimalis, 217
   lingualis, 220
   lumbar, 225
   median coccygeal, 232
     hemorrhoidal, 227
   meningeal, 216
   mesenteric, 227
   muscularis, 207
   occipital, 216
   occipitalis profunda, 216
     sublimis, 216
   ophthalmica externa, 216
   ovarian, 226
   plexus palpebralis, 217
     temporalis, 216
   posterior aorta, 224
     circumflex humeral, 223
     mesenteric, 227
     vertebral, 221
   profunda communis, 231
     penis, 232
   pudenda externa, 232
   pulmonalis dexter, 213
     sinister, 213
   pulmonary, 213
   radial, 223
   ramus anterior, 217
     posterior, 217
     profundus, 209
     superficialis, 209
   recurrent ciliaris posticus, 217
     ilio-celiacus, 227
     intestinalis, 227
     renalis, 229
     sinister, 227
     superior hemorrhoidal, 227
     ulnar, 223
   renal, 226
   retinæ centralis, 217
   sacralis media, 229, 232
   spermatic, 226
   sphenoid, 217
   spheno-maxillaris, 217
   splenic, 227
   sternal, 222
   sterno-clavicularis, 221
   subclavian, 212
   subcutaneous colli, 215
   subscapular, 222
   superior cervical, 215
     laryngeal, 218
   sylvian, 217
   temporal, 216
   thoracic, 222
   thyroid, 215
   tibialis antica, 230
     postica, 230
   ulnar, 223
   umbilical, 228
   vertebral, 215

 Arthrology, 56

 Articulo-jugale, 58

 Arytenoid cartilage, 194

 Atlas, 37

 Auricle, 324

 Auricular appendage, 208
   meatus, 305
   ossicles, 305
   ventricular valve, 207

 Axial skeleton, 23

 Axillaris nerve, 23

 Axis, 37
   cylinder process, 277

 Axolemma, 277

 Axone, 277
   hill, 277


 Barbes, 310

 Barbules, 310

 Basi-branchial bone, 35

 Basi-hyal bone, 33, 36

 Basilar artery, 217

 Beak, 139, 310, 316

 Biceps band, 114
   brachii, 104
   flexor cruris, 113

 Biventer cervicis muscle, 77, 83

 Blastema, 322

 Blastoderm, 318

 Blood, 257
   coagulation, 260
   composition, 260
   formation, 260
   function, 257
   plasma, 260
   reaction, 257
   vascular system, 206
   vessels, 209

 Bloom, 188

 Bone or bones, 17
   atlas, 37
   axis, 37
   cancellous, 18
   carpus, 44, 47
   classification, 20
   compact, 17
   composition, 21
   cervical vertebræ, 35, 37
   coccygeal, 35, 41
   dorsal vertebræ, 35, 39
   entoglossal, 35
   ethmoidal, 23, 27
   femur, 50
   fibula, 53
   flat, 21
   frontal, 23, 29
   furculum, 24
   growth, 20
   humerus, 44, 45
   hyoid, 35, 36
   ilium, 49
   inferior maxilla, 23, 34
   irregular, 21
   ischium, 49
   jugale, 23, 31, 33
   lacrimal, 23, 31, 33
   long, 20
   lumbo-sacral, 35, 39
   maxillæ, 23, 31, 32
   metacarpus, 44, 47
   metatarsus, 53
   nasal, 23, 31, 32
   occipital, 23, 35
   of cranium, 23
   of face, 31
   of fore limb, 44
   of hind limb, 50
   of pelvis, 48
   of shoulder, 43
   of skull, 23
   of thorax, 42
   of vertebræ, 26
   palatine, 23, 31, 33
   parietal, 23, 29
   phalanges, 44, 47
   premaxilla, 23, 31
   pterygoid, 23, 31, 33
   pubis, 50
   pygostyle, 24
   quadrate, 23, 34
   quadrate-jugale, 23, 33, 36
   radius, 44, 46
   ribs, 41
   scapular arch, 40
   sesamoid, 54
   sphenoid, 25, 28
   supplied with air, 204
   tarsus, 53
   temporal, 23, 29
   tibia, 52
   turbinated, 34, 193
   ulna, 44, 46
   vomeral, 23, 31, 32
   zygomatic, 23, 31, 32

 Bowman’s capsule, 171

 Brachial nerve plexus, 282

 Brain, 288
   alæ cinereæ, 291
   anterior commissure, 296
   aqueduct of Sylvius, 289
   arbor vitæ, 291
   calamus scriptorius, 290
   cerebral peduncles, 291
   choroid plexus, 296
   corpora restiformia, 289
   corpus callosum, 296
     striatum, 296
   coverings, 288
   crura cerebelli, 291
     cerebri, 289
   fore, 290
   fourth ventricle, 290
   hind, 290
   hippocampus, 297
   hypophysis, 289
   inferior pyramids, 291
   lamina terminales, 295
   lateral ventricles, 297
   medulla oblongata, 290
   mid-, 290
   nervi amygdales, 296
   optic chiasm, 289
     lobes, 289
   pars commissuralis, 289
   pons varolii, 289
   processus cerebri mammillares, 297
   pyramidal columns, 291
   sulcus centralis, 291
   superior pyramids, 291
   thalami optici, 289
   tubercula olfactoria, 297
   valve of Vieussens, 290
   ventricles, lateral, 297

 Bronchi, 193, 197
   diaphragmatic, 197

 Bronchial artery, 215
   tubes, 197

 Bronchialis anticus, 89, 105
   longus inferior nerve, 284
     superior nerve, 283
   posticus, 89

 Broncho-trachealis anticus, 38
   brevis, 89

 Brunner’s glands, 149

 Bulla tympaniformis, 195

 Bursa of Fabricius, 152


 Cæca, 151

 Calamus, 310
   scriptorius, 290

 Canal or canals, caroticus et jugulare, 27
   Haversian, 17
   hypotarsal, 53
   ilio-lumbalis, 48
   neural, 38
   of Petit, 305
   urinary, 170
   Volkmann’s, 17

 Canaliculi, 17

 Cancelli, 17

 Capillaries, 209

 Capsular ligament, 57

 Caput costæ, 42

 Carotid trunk, 215

 Carotin, 314

 Carotis cerebralis artery, 215
   communis, 215
   externa artery, 215

 Carpi radiale, 47
   ulnare, 47

 Carpus, 44, 47

 Cartilage semi-lunaris, 69

 Cavity, cotyloid, 49
   glenoid, 44
   glenoidalis interna, 67
   nasal, 35
   sigmoid, 46

 Cavum cranii, 23
   ilio-lumbale dorsales, 48

 Celiac axis, 226

 Cera, 310

 Cerato-branchial cartilage, 35

 Cerato-glossus muscle, 80

 Cerato-hyoideus muscle, 80

 Cerebellar cortex, 293

 Cerebellum, 25, 295

 Cerebral lobes, 322
   peduncles, 291

 Cerebro-spinal axis, 288
   nervous system, 265

 Cerebrum, 25

 Ceroma, 37

 Cervical air-sac, 201
   artery, superior, 215
   nerve ganglion, 270
   sympathetic nerve ganglion, 275
   vertebræ, 35, 37

 Chalazæ, 180

 Chamber, nasal, 193

 Chorion, 321, 327

 Choroid coat, 323

 Choroidea, 303

 Chromophilic bodies, 280

 Chromosomes, 318

 Ciliary ganglion, 271
   nerve, 304
   process, 304, 323

 Circulatory system, 206

 Circumconcha muscle, 128

 Circumduction, 57

 Clavicle, 44

 Clavicular artery, 222

 Claws, 310

 Cleido-trachealis muscle, 75

 Cloaca, 151

 Clothing feathers, 310

 Coccygeæ laterales arteries, 232
   vertebræ, 33, 41

 Cochlearis, 305

 Collum costæ, 42

 Color of skin, 314

 Columella, 31, 305

 Column, vertebral, 35

 Columnæ carnæ, 207

 Complex nerve ganglion, 271

 Complexus muscle, 81

 Composition of bone, 21
   of egg, 181

 Condyle, external, of femur, 50
   inner, of femur, 51

 Conjunctiva, 303

 Constrictions of Ranvier, 277

 Coprodeum, 151

 Coraco-brachialis muscle, 103

 Coraco-humeralis muscle, 101

 Coracoid bone, 194

 Corium, 313

 Cornea, 323

 Corneum, 309

 Cornu, hyoid, 35

 Coronary artery, 209

 Corpora restiformia, 289

 Corpus ciliare, 303

 Costal bronchial tubes, 197
   process of sternum, 24

 Cotyloid cavity, 65

 Course of food, 152

 Cranial cavity, 23

 Cranium, 23

 Cricoid, 194

 Crico-trachealis ligament, 194

 Cristiilii, 48
   sterni, 42

 Crop, 142

 Crura cerebelli, 291
   cerebri, 289

 Crural artery, 228
   nerve plexus, 283

 Crystalline lens, 303, 304, 303, 322, 323

 Cuneiform bone, 46

 Cutaneous brachii superior nerve, 283
   follicle, 323

 Cutis, 313


 Deglutition, 143

 Deltoid, 104

 Dendrites, 297

 Depressor caudæ muscle, 95
   coccygis muscle, 95
   glossus muscle, 80
   palpebræ inferioris, 125

 Derivatives of germ layer, 342

 Dermis, 313

 Dermo-cleido dorsalis, 75

 Dermo-dorsalis, 72

 Dermo-frontalis, 72

 Dermo-humeralis, 72

 Dermo-iliacus, 75

 Dermo-pectoralis, 73

 Dermo-spinalis, 75

 Dermo-temporalis, 73

 Dermo-tensor patagii, 72

 Dermo-ulnaris, 76

 Diaphragm, 165

 Diaphragmatic bronchial tubes, 197

 Diapophysis, 38

 Digastric muscle, 78

 Digestive apparatus, 135

 Digits, 54

 Dissection, 343
   laboratory, 351
   of arteries, 345
   of bone, 346
   of muscles, 343
   of nerves, 347
   of viscera, 344

 Division of skeleton, 22

 Dorsal ligament of oviduct, 188
   vertebræ, 35

 Dorso-cutaneous nerve plexus, 283

 Ductless glands, 148, 329
   adrenal, 191
   parathyroid, 191
   spleen, 155
   thymus, 190

 Ductus arteriosus, 325, 329
   Botalli, 214

 Duodenum, 148, 150

 Dura mater, 288


 Ear labyrinth, 305

 Ectoderm, 320

 Efferent nerves, 300

 Egg, 180
   composition, 181
   tooth, 327

 Embryology, 318

 Endocardium, 206, 207, 208

 Endolymph, 306

 Endothelium, 206

 Entoderm, 320

 Entoglossal bone, 35

 Entotympanic, 77

 Epicondyloid fossa, 52

 Epidermis, 176, 207, 313

 Epididymis, 176

 Epineural appendage, 38

 Equipment, 351

 Erythrocytes, 258
   fate of, 261

 Esophageal artery, 224
   inferior, 215

 Esophagus, 142

 Esthesiology, 303

 Ethmoid bone, 27

 Eustachian tube, 29, 136

 Extensor annularis brevis muscle, 121
   brevis digitorum muscle, 120
   digitorum communis muscle, 106
   femoris muscle, 113
   hallucis brevis muscle, 119
   indicis longus muscle, 108
   longus digitorum muscle, 119
   metacarpi radialis longior muscle, 105
   ossis metacarpi pollicis muscle, 107
   proprius pollicis muscle, 109

 External facial artery, 220
   thoracic artery, 222

 Extremitas vertebralis, 42


 Fabricius, bursa of, 152

 Facial artery, 220

 Falx cerebri, 289

 Fasciculi, 70, 71
   deep, 71
   superficialis, 71

 Feathers, 311
   alula, 311
   coverts, 311
   primaries, 311
   rectrices, 311
   rudder, 41
   scapularies, 311
   secondaries, 311
   tertiaries, 311

 Female generative organs, 178

 Femoral artery, 228

 Femoro-caudal, 114

 Fenestra ovalis, 31
   rotunda, 31
   vestibularis, 105

 Fertilization, 318, 319

 Fetal circulation, 329

 Fibers of Sharpey, 20

 Fibrin ferment, 261
   formation, 261

 Fibrinogen, 261

 Fibrino-globulin, 261

 Fibular bone, 53
   ridge, 52

 Fifth cranial nerve, 268
     inferior maxillary division, 268
     ophthalmic division, 268
     superior maxillary division, 268

 Filiform papillæ, 41

 Filo-plume, 311

 Flesh, 70

 Flexor brevis pollicis muscle, 109
   capitis inferior muscle, 82
   carpi ulnaris brevior muscle, 109
     muscle, 108
   digitorum profundus muscle, 108
     sublimis muscle, 108
   hallucis brevis muscle, 121
     longus muscle, 122
   metacarpi brevis muscle, 111
     radialis muscle, 106
   minimi digiti muscle, 110
     brevis muscle, 110
   perforans digitorum profundus muscle, 124
   perforatus annularis primus pedis muscle, 122
     indicis primus pedis, 123
     medius primus pedis, 123
       secundus pedis, 121, 122

 Fontanel, 27

 Foramen intervertebralis, 39
   ischiadic, 24, 49
   magnum, 23
   Monro, 295
   nutrient, 52
   oblongum, 24
   optic, 27
   ovale, 306, 207, 329
   pneumatic, 42, 43, 45
   triossium, 44, 61

 Fore brain, 290
   limb, 44

 Fossa anterior, 25
   articularis transversa, 54
   cranii media, 25
     posterior, 25
   epicondyloid, 52
   epitrochlear, 51
   intercondyloid, 51
   middle, 25
   ovalis, 207
   pneumatic, 45
   posterior, 25
   subcondyloid, 27
   trochanteric, 50

 Fourth ventricle, 290

 Fovea cardiaca, 324
   ischiadica, 48
   lumbalis, 48
   pudendalis, 48

 Fowl skeleton, 21

 Frontal bone, 29

 Function, centers of, 301
   muscles of, 128

 Funnel portion of oviduct, 183

 Furculum bone, 24


 Gall-bladder, 154

 Ganglion, 300
   cardiacum, 299
   cervical, 270
     sympathetic, 275
   ciliary, 271
   complex, 271
   Gasserian, 268
   geniculate, 271
   inferior cervical, 299
   orbito-nasal, 270
   petrosal, 272
   spheno-palatine, 270
   spinal, 276
   structure of, 277
   superior cervical, 299
     sympathetic, 272
   thoracic, 299
   vagi radicis, 272

 Gastrocnemius muscle, 117

 Gemellus muscle, 116

 Genio-hyoideus muscle, 79

 Genital system, 169

 Germ layer, 342

 Gland, alveolar, 141
   angular, 141
   ductless, 190
   lacrimal, 303
   meibomian, 303
   mouth, 141
   mucous, 136
   oil, 41
   pharynx, 141
   sublingual, 141
   thymus, 190
   thyroid, 190
   uropygii, 309

 Glosso-hyal element, 35

 Glottis, 194

 Gluteus medius muscle, 112
   minimus muscle, 112
   primus muscle, 112
   profundus muscle, 112

 Gray matter of cord, 292

 Groove, angular, 52
   tendonal, 54

 Growth of bone, 20


 Hallux, 54

 Hand, 47

 Hard palates, 136, 139

 Haversian canals, 17

 Heart, 206
   structure of, 207
   ventricles of, 324

 Hemal arch, 38

 Hemapophysis, 38

 Hemophage, 262

 Hemorrhoidalis intima artery, 232

 Henle’s limb, 171
   loop, 171

 Hepar, 153

 Herbst’s corpuscles, 307

 Hind brain, 290
   limb, 50

 Hormone, 190

 Humerus, 44, 45

 Hyoid, 218
   arch, 324
   bone, 35

 Hyoideus transversus muscle, 80

 Hypapophysis, 38

 Hypocleidum, 24, 44

 Hypoglossal nerve, 274

 Hypophysis, 289, 295

 Hyporachis, 313

 Hypotarsal canal, 53

 Hypotarsus, 53


 Ilio-lumbalis dorsalis, 48

 Ilium bone, 49

 Immovable joints, 56

 Inferior alveolar artery, 220
   cerebellar artery, 217
   larynx, 193
   maxillary bone, 34
   pyramids, 291
   thoracic artery, 222
   tuberculum ossis carpi radialis, 47

 Infracoccygis muscle, 96

 Infraorbital sinus, 32

 Ingluvies, 142

 Inner ear, 306

 Interarticulares muscles, 85

 Intercostal arteries, 224
   nerve, 285

 Intercostales muscles, 98

 Internal adhesio cornu antici cartilaginis lunatæ, 67
   ethmoidal artery, 218
   facial artery, 220
   mammary artery, 222
   mandibular vein, 237
   maxillary artery, 220
   ophthalmic artery, 217, 218
   pelvic artery, 228
   secretion, 190
   thoracic artery, 222

 Interosseous ligament, 58

 Interosseus dorsalis muscle, 110
   palmaris muscle, 111

 Interspinales muscles, 85

 Intertransversales muscles, 86

 Intestine, free portion, 150
   large, 150
   small, 147

 Intestinum tenue, 147

 Iris, 323, 303, 304

 Ischiadic artery, 229
   foramen, 49
   nerve, 286

 Ischium, 49

 Isthmus, 186


 Joints, 56
   immovable, 56
   mixed, 56
   movements, 56

 Jugal bone, 23, 31, 33

 Jugular vein, 233


 Kerato-hyalin, 314

 Kerato-hyoideus muscle, 80

 Kidneys, 169


 Lacrimal bone, 23, 31, 33
   duct, 303
   gland, 303
   sac, 303

 Lacunæ, 17

 Lamellæ, 17
   circumferential, 17
   concentric, 17
   interstitial, 17

 Lamina perpendicularis, 28

 Laminæ terminale, 29

 Langerhans, islands of, 303

 Large intestine, 150

 Larynx, 141
   bronchio-trachealis, 194
   false, 194
   inferior, 193
   superior, 193
   true, 194

 Lateral process, 38

 Lateralis caudæ muscle, 95
   coccygeus muscle, 95

 Latissimus dorsi muscle, 96
   nerve plexus, 282

 Leucocytes, 258
   basophile, 259
   eosinophile, 258
   lymphocyte, 259
   mast cell, 259
   mononuclear, 259
   polymorphonuclear, 258

 Levator caudæ muscle, 93
   coccygis muscle, 93
   palpebræ superioris muscle, 124
   scapulæ muscle, 103

 Levatores costarum muscle, 98

 Lien, 155

 Ligament or ligaments, 57
   annular, 58
   annulare radii, 61
   anterior cruciatimi genu, 69
   anterius ossis carpi metacarpi et primæ, 69
       phalangis digiti secundi, 64
     patellar, 67
   antero-inferior humero-coracoideum, 61
   anticum, 69
   articulo-jugale, 58
   capsular, 57
   capsulare atlantico-epistrophicum odontoideum, 59
     atlantico-occipitale, 58
     capituli fibulæ, 68
     cubiti, 61
     digitorum pedis, 69
     obliquum, 59
     ossis tibio-metatarsi, 69
   carpi interosseum, 64
     radialis internum, 64
   claviculosternal, 44
   coraco-furculare, 61
   coraco-humeralis, 61
   coraco-scapulare, 61
     inferius, 61
     internum, 61
   crico-trachealis, 194
   cubiti teres, 62
   elasticum interspinale profundum, 59
     superficiale, 59
   externum, 69
   extero-laterale genu, 65
   furculo-scapulare, 61
   humero-scapulare, 61
   ilio-pubic, 65
   ilio-sacrale, 65
   inferius, 61
   internum, 64
   intero-laterale genu, 66
   interosseous, 58
   interosseum, 69
   intervertebral, 38
   laterale cubiti externum, 61
     internum, 61
   nuchæ, 59
   obliquo-carpi ulnaris, 62
   of carpal joint, 61
   of ear, 58
   of elbow-joint, 59
   of finger, 64
   of hip-joint, 65
   of jaws, 58
   of knee-joint, 65
   of liver, 153
   of oviduct, 188
   of pelvis, 56
   of ribs, 59
   of shoulder-joint, 59
   of sternum, 59
   of tibio-metatarsal joint, 69
   of toes, 69
   of vertebræ, 58
   ossis carpi radialis internum et metacarpi, 64
     ulnaris externum et metacarpi, 64
       internum et metacarpi, 64
   pollicare, 64
   popliteum, 67
   posterior cruciatum genu, 67
   posterius, 64
   posticum ulnare carpi ulnaris, 63
   Poupartii, 65
   radiale carpi radialis externum, 64
   structure, 57
   superius, 69
   suspensorium corporum vertebralium, 58
   suspensorium dentis epistrophei, 58
   tibio-fibulare, 68
   transversale commune, 67
   transversum, 59
     atlantis, 58, 59
     externum, 59
   triangulare, 59
   ulnare carpi radialis, 63
       internum, 63
     metacarpi externum, 64
       internum, 64

 Limb, fore, 44
   hind, 50

 Lingua, 139

 Linguales arteries, 220

 Lipochrome, 314

 Liquor pericardii, 207
   sanguinis, 258

 Liver, 152, 153
   ducts, 155

 Longissimus capitis et atlantis, 85
   dorsi, 92

 Longus colli dorsalis muscle, 83
   muscle, 83
   posticus muscle, 83

 Lumbar arteries, 225

 Lumbo-sacral vertebræ, 35, 39

 Lumbo-sacrales nerves, 285

 Lung, 195, 325
   tubules, 197, 199
     primaries, 197
     secondaries, 198
     tertiaries, 198

 Lymph vascular system, 206, 254

 Lymphocytes, 259


 Malaris muscle, 125

 Male generative organs, 175

 Malpighian body, 155, 156, 171

 Mandibular arch, 324

 Marrow, 20
   red, 20
   yellow, 20

 Masseter muscle, 77

 Mast cells, 259

 Maxilla, 23, 31, 32

 Maxillary arch, 324

 Median coccygeal artery, 323
   hemorrhoidal artery, 227
   nerve, 284

 Medulla oblongata, 25, 290
   ossium flava, 20
     rubrum, 20

 Meibomian glands, 303

 Melanin, 316

 Membrana nictitans, 303, 324
   putaminæ, 329
   semi-lunaris, 195
   testacea, 187
   tympana interna, 195

 Membranæ obturatoræ intervertebrales posteriores, 59

 Meningeal artery, 216

 Meninges, 288

 Meniscus, 56
   intervertebralis, 58

 Mesentery, 156, 157

 Metacarpus, 44, 47

 Metasternum, 42

 Mid brain, 290

 Middle fossa of cranium, 25
   meningeal artery, 217

 Molting, 313

 Motor oculi, 267

 Mouth, 135

 Movable joints, 56

 Mucous glands, 136

 Müllerian duct, 184

 Muscle or muscles, 70
   abductor minimi digiti, 110
   adductor longus, 117
     magnus, 117
   anconeus, 107
   biceps, 104
     flexor crurus, 113
   biventer cervicis, 83
     maxillæ, 77
   brachialis anticus, 105
   bronchialis anticus, 89
     posticus, 89
   broncho-trachealis anticus, 88
     brevis, 89
     posticus, 89
   cerato-glossus, 80
   cerato-hyoideus, 80
   ciliary, 304
   cleido-trachealis, 75
   complexus, 81
   constrictor glottidis, 87
   coraco-brachialis, 102
   coraco-humeralis, 101
   deltoid, 104
   depressor caudæ, 95
     coccygis, 95
     glossus, 80
   dermal, 70, 71
   dermo-cleido-dorsalis, 75
   dermo-dorsalis, 72
   dermo-frontalis, 72
   dermo-humeralis, 72
   dermo-iliacus, 75
   dermo-osseous, 70, 73
   dermo-pectoralis, 73
   dermo-spinalis, 75
   dermo-temporalis, 73
   dermo-tensor patagii, 72
   dermo-ulnaris, 76
   diaphragm, 90
   digastricus, 78
   entotympanic, 77
   expansor secundarium, 62
   extensor digitorum communis, 106
     femoris, 113
     indicis longus, 108
     metacarpi radialis longior, 105
     ossis metacarpi pollicis, 107
     proprius pollicis, 107
   femoro-caudal, 114
   flexor brevis pollicis, 109
     capitis inferior, 82
     carpi ulnaris, 108
       brevior, 109
     digitorum sublimis, 108
     metacarpi brevis, 111
       radialis, 106
     minimi digiti, 110
       brevis, 110
     profundus, 108
   gastrocnemius, 117
   gemellus, 116
   genio-hyoideus, 79
   gluteus maximus, 50
     medius, 112
   gluteus minimus, 112
     primus, 112
   heart, 71
   hyoideus transversus, 80
   infracoccygis, 96
   interarticulares, 85
   internal obturator, 49
   interosseus dorsalis, 110
     palmaris, 111
   interspinales, 85
   intertransversales, 86
   involuntary, 70
     striated, 71
   lateralis caudæ, 95
     coccygis, 95
   latissimus dorsi, 96
   levator caudæ, 93
     coccygis, 93
     scapulæ, 103
   levatores costarum, 98
   longissimus dorsi, 92
   longus colli anticus, 84
     posticus, 83
   masseter, 77
   mylo-hyoides, 79
   nomenclature, 71
   obliquo-transversales, 82
   obliquus abdominis externus, 90
       internus, 91
     colli, 83
   obturator externus, 116
     internus, 116
   of abdomen, 90
   of air passage, 86
   of anterior pectoral region, 99
   of brachial region, 104
   of cervical region, 81
   of coccygeal region, 93
   of costal region, 96
   of digit, 109
   of dorso-lumbar region, 92
   of forearm and hand, 105
   of head, 76
   of inferior larynx, 86
   of pectoral region, 100
   of posterior limb, 111
   of scapular region, 101
   of sternum, 90
   of superior larynx, 86
   of tibial region, 117
   of tongue, 79
   pectoralis major, 100
     secundus, 100
     tertius, 100
   peroneus longus, 118
   platysma myoides, 74
   pronator brevis, 107
     longus, 107
   pterygoideus externus, 78
     internus, 78
     lateralis, 78
     medius, 74
   rectus abdominis, 91
     capitis anticus minor, 81
       lateralis, 84
       posticus major, 82
   rhomboideus, 17
   sacro-lumbalis, 92
   sartorius, 111
   scalenus medius, 86
   scapulo-humeralis, 101
   semimembranosus, 114
   semitendinosus, 114
     accessorius, 114
   serratus magnus anticus, 97
     parvus anticus, 97
   skeletal, 70, 76
   soleus, 118
   sphincter, pupillary, 304
   sterno-trachealis, 89
   stylo-hyoideus, 79
   subclavius, 102
   subscapularis, 103
   supraspinatus, 102
   temporal, 76
   tensor patagii brevis, 99
     longus, 99
   teres et infraspinatus, 98
     minor, 102
   thoraco-scapularis, 103
   thyreo-arytenoideus, 85
   trachelo-mastoideus, 85
   tracheo-lateralis, 87
   transversalis abdominis, 90
   transversus peronei, 94
   trapezius, 97
   triceps, 104
   true dermal, 71
   voluntary-striated, 70

 Myelon, 322

 Myeloncephalus columns, 320

 Myocardium, 208


 Nails, 316

 Nasal bone, 23, 31, 32
   cavity, 35
   chambers, 193

 Naso-premaxillary process, 324

 Nerve or nerves, 264
   abducens, 70
   accessorius spinalis, 274
   acoustic, 271
   afferent, 300
   alveolar, 270
   anterior coraco-brachialis, 284
     spinal branches, 281
     thoracic, 284
   axillaris, 283
   brachial plexus, 282
   brachialis longus inferior, 284
     superior, 283
   cells, 280
   centers, 30
   ciliary, 304
   cranial, 265
   crural plexus, 285
   cutaneous brachialis et inferior brachialis, 284
     brachii superior, 283
   dorsal spinal, 281
   dorsalis plexus, 282
   dorso-cutaneous plexus, 283
   efferent, 300
   ethmoidalis, 269
   facialis, 286
   function, 300, 301
   furcularis, 286
   glosso-pharyngeal, 272
   hypoglossal, 27, 37, 274
   intercostal, 285
   ischiadic, 49, 286
   latissimus dorsi, 282
   lumbo-sacral, 285
   median, 284
   medullated, 277
   motor oculi, 267
   neurolemma, 277
   non-medullated, 277
   obturator, 286
   olfactorius, 34, 265
   optic, 267
   patheticus, 268
   peroneus profundus, 287
   plexus pedundus, 288
   pneumogastric, 273
   posterior coraco-brachialis, 284
   ramus secundus, 269
   recurrent cardiacus, 274
     externa, 269
     hepatici, 274
     infra-orbitale, 269
     laryngeus, 274
     linguales, 273
     pharyngeus, 272
     pulmonale, 274
     subcutaneous, 270
     ventralis, 281
   rhomboideus profundus, 282
     superficialis, 282
   scapulo-humeralis, 282
   serratus plexus, 282
   spinal cord, 275
   sterno-coracoideus, 284
   subcoraco-scapularis, 282
   superficialis peroneus, 287
     serratus, 282
   supra-coracoideus, 283
   trifacial, 31, 268
   ulnar, 284
   vagus, 27, 31, 273
     group, 273

 Nerve trunks, structure of, 277

 Nervous system, 264, 300

 Neural arch, 38
   spines, 38, 39

 Neurofibrils, 280

 Neurones, 268, 279

 Nostril, 193

 Notocord, 322


 Oblique process, 39

 Obliquo-transversales muscle, 86

 Obliquus abdominis externus muscle, 90
     internus muscle, 91
   dorsalis, 125
   inferior, 127
   superior, 125
   ventralis muscle, 121

 Obturator externus, 116
   internus, 116
   nerve, 286

 Occipital artery, 215
   bone, 23, 25

 Occipitale laterales bone, 25

 Occipitalis inferius bone, 25
   profunda artery, 215
   sublimis artery, 215
   superioris bone, 25

 Odontoid process, 37

 Oil gland, 41

 Olecranon, 46

 Olfactory cavities, 322
   cerebral crura, 295
   glomeruli, 265
   nerve, 265

 Oögenesis, 319

 Ophthalmic vesicle, 322

 Ophthalmica externa, 216

 Optic chiasm, 289
   lobes, 322, 289
   nerve, 267

 Orbicularis oculi, 124
   palpebrarum muscle, 124

 Orbit, 323

 Orbital process, 30

 Orbito-nasal ganglion, 270

 Organ of hearing, 304, 322
   of sight, 303
   of smell, 307
   of taste, 307
   of touch, 307

 Os angulare, 30
   articulare, 30
   transversale, 105

 Osseous structure, 17
   tissue, 17

 Ostium tubæ abdominale, 183

 Otocrane, 323

 Otoliths, 322

 Ovarian artery, 226
   pocket, 189

 Ovary, 325

 Oviduct, 182, 325

 Ovum, 318


 Palatal papillaries, 141

 Palatine glands, 141

 Palatinus bone, 23, 31, 33

 Palatum durum, 139

 Palpebral plexus, 217

 Pancreas, 152, 155

 Papilla, 141

 Parapophysis, 38

 Parietal bone, 29

 Pars commissuralis, 289
   glandularis, 143
   muscularis, 143
   renalis, 251

 Partes pedunculares, 294

 Patella, 53

 Patheticus, 268

 Pecten, 303, 323

 Pectoralis major, 100
   secundus, 100
   tertius, 101

 Pelvic cavity, 156
   girdle, 48

 Pericardium, 207

 Perimysium, 70

 Periosteum, 18

 Peritoneum, 156

 Peroneus longus, 118
   nerve, 287

 Pessulus, 195

 Petrosal ganglion, 272

 Phalanges, 44, 47, 54

 Pharynx, 54, 141

 Pia mater, 288

 Pineal gland, 295

 Pituitary body, 25, 289, 295

 Placenta, 321

 Planum coccygeum, 48

 Plasma, 261

 Platysma myoides muscle, 74

 Pleurapophysis, 38

 Plexus, abdominal, 299
   anterior splanchnic, 300

 Plexus, lacrimal, 217
   mesenteric, 299
   muscularis, 217
   pedundus, 288
   posterior splanchnic, 300
   thoracic, 299

 Plica primitivæ, 320

 Pneumatic foramen, 42, 43, 45

 Pons varolii, 289

 Post-acetabular ridge, 48

 Posterior aorta, 224
   circumflex artery, 223
   diaphragmatic air-sac, 202
   fossa, 25
   nares, 136
   orbitalis, 30
   vena cava, 247
   vertebral artery, 221
     vein, 234

 Poupart’s ligament, 65

 Prezygapophyses, 39

 Primaries, 311

 Primitive streak, 321

 Process, costal, 43
   lateral, 37, 39
   oblique, 37, 39
     of sternum, 42
   odontoid, 37
   xiphoid, 43

 Processus acusticus externus, 31
   ciliaris, 304
   coracoideus, 44
   cubitalis humeri, 45
   frontalis, 32
     anterior, 32
     posterior, 32
   furcularis, 43
   humeralis, 43
   intermaxillaris, 32
   ischiadicus, 49
   maxillaris, 32
     anterior, 32
   odontoid, 37
   olecranalis coracoideus, 46
   orbicularis, 28, 29
   orbitalis, 29
   palatinus, 32
   posterior orbitalis, 30

 Processus uncinatus, 24
   zygomaticus, 28, 30

 Profunda penis, 232

 Pronation, 57

 Pronator brevis muscle, 107
   longus, 107

 Proteids of plasma, 261
   of serum, 261

 Proventriculus, 143

 Provertebra, 320

 Pterygoideus externus muscle, 78
   internus muscle, 78
   lateralis muscle, 78
   medialis muscle, 78

 Pterylæ, 311

 Pubis, 50

 Pudenda externa artery, 232

 Pulmonalis dextra, 213
   sinistra, 213

 Pulmonary artery, 213
   vein, 233

 Pulp, 311

 Punctum saliens, 320

 Purkinje cells, 293

 Pyramidal columns, 291


 Quadrate, 34

 Quadrato-jugale, 23, 31, 33

 Quadratus nictitans, 125

 Quill, 310
   feathers, 310


 Rachis, 310, 313

 Radial artery, 223

 Radius, 44, 46

 Rami communicantes, 276
   glottis, 194

 Ramus ascendens ossis ischii, 49
   ciliaris posticus, 217
   posterior artery, 217
   profundus artery, 209
   superficialis artery, 209

 Rectrices, 41, 311

 Rectus abdominalis muscle, 91
   capitis anticus minor muscle, 81
     dorsalis major muscle, 82
     posticus major muscle, 82

 Rectus capitis ventralis muscle, 82
   dorsalis muscle, 127
   externus muscle, 127
   inferior muscle, 127
   internus muscle, 128
   lateralis muscle, 127
   medialis muscle, 128
   superior muscle, 127
   ventralis muscle, 127

 Recurrent cardiacus nerve, 274
   hepatici nerve, 274
   infraorbital nerve, 269
   intestinalis nerve, 227
   laryngeus nerve, 273
   lingualis nerve, 273
   pharyngeus nerve, 272
   pulmonale nerve, 274
   renal artery, 223
   renales nerves, 229
   sinister artery, 227
   subcutaneous nerve, 270

 Red blood cells, 258
   shape, 258
   size, 259
   structure, 259

 Reflex action, 301

 Renal artery, 226
   corpuscle, 171

 Respiratory apparatus, 193

 Rete malpighii, 313

 Retina, 303, 304, 323

 Rhomboideus muscle, 97
   profundus nerve, 282
   superficialis nerve, 282

 Ribs, 41
   false, 41
   true, 41

 Ridge, ectonemial, 52
   fibrillar, 52
   post-acetabular, 48
   procnemial, 52
   trochanteric, 50

 Rotation, 57

 Round ligament, 65

 Rudder feathers, 41


 Sacralis media artery, 229, 232

 Sacro-lumbalis muscle, 92

 Sacs, air, 199

 Sarcolemma, 70

 Sartorius muscle, 111

 Scala tympani, 306
   vestibuli, 306

 Scalenus medius muscle, 86
   muscle, 86

 Scapho-lunar bone, 47

 Scapula, 43

 Scapulo-humeralis muscle, 101
   nerve plexus, 282

 Sclerotic coat, 303, 304

 Secondaries, 311

 Secretion, internal, 190

 Semilunar cartilage, 67

 Semimembranosus muscle, 114

 Seminiferous tubules, 318

 Semitendinosus muscle, 114
   accessorius muscle, 114

 Sense of hearing, 305
   of sight, 303
   of smell, 307
   of taste, 307
   of touch, 307
   organ, 303

 Sensory nerves, 300

 Septum nasi, 33

 Serous cavity, 156
   membrane, 156
   sac, 156

 Serratus magnus anticus muscle, 97
   nerve plexus, 282
   parvus anticus muscle, 97

 Serum, 261
   albumin, 261
   globulin, 261

 Sesamoid bone, 54

 Sharpey’s fibers, 20

 Sheath of Schwann, 277

 Shell bloom, 188
   gland, 187
   membrane, 181
   structure, 181
   tint, 181

 Shoulder girdle, 43

 Sinus foraminis occipitales, 240
   foveæ hemispherii cerebelli, 241
   infraorbitalis, 32

 Sinus longitudinalis, 239
   occipitalis, 240
     externus, 240
   petrosus sphenoideus, 240
   rhomboideus, 276
   semicircularis, 240
   temporales, 332
   temporo-sphenoideus, 240
   transversus, 240
   venosus annularis basilaris, 240

 Skeleton, 21, 24
   appendicular, 43
   axial, 22
   division, 22

 Skin, 309, 323

 Small intestine, 147

 Smooth muscle, 70

 Soleus muscle, 118

 Somatic cell, 318

 Spermatic artery, 226

 Spermatids, 318

 Spermatocyte, 318

 Spermatogenesis, 318

 Spermatogonia, 318

 Spermatozoa, 176, 318

 Sphenoid artery, 217
   bone, 28
   rostrum, 29

 Spheno-maxillary artery, 217

 Spheno-palatine nerve ganglion, 270

 Spinal cord, 38
   nerves, 281
   nervous system, 264

 Splanchnology, 135

 Splanchnopleure, 327

 Spleen, 152, 155

 Splenic artery, 227
   capsule, 155
   pulp, 155

 Spur, 54, 317

 Squamous epithelium, 137

 Sternal artery, 222

 Sterno-clavicularis artery, 221
   muscle, 284

 Sterno-coracoideus nerve, 284

 Sterno-hyoideus muscle, 80

 Sterno-trachealis muscle, 89

 Sternum, 42

 Stigmen, 179

 Stomach, 143

 Stratum corneum, 141, 313, 314
   germinativum, 314
   granulosum, 314
   lucidum, 344
   Malpighii, 314

 Stylo-hyoideus muscle, 79

 Styloid process of ulna, 46

 Subclavian artery, 234

 Subcondyloid fossa, 27

 Subcoraco-scapularis nerve, 282

 Subcutis, 309

 Subscapularis artery, 222

 Succus entericus, 152

 Sulcus ilio-lumbalis dorsalis, 48
   centralis, 291, 294
   longitudinalis, 291

 Superficialis peroneus nerve, 287
   serratus nerve, 282

 Superior laryngeal artery, 218
   larynx, 193
   median fissure of cord, 276
   pyramidalis, 291
   sympathetic ganglion, 272
   tuberculum ossis carpi radialis, 47

 Supra-coracoideus nerve, 283

 Sylvian artery, 217

 Sympathetic caroticus cephalicus, 298
   nervous system, 264, 297
   ophthalmic plexus, 298
   recurrent cardiacus, 299
   temporo-lacrimalis, 298
   thoracic trunk, 299

 Symphysis ilio-sacralis, 49
   ilio-sacri, 49

 Synovial apparatus, 57, 156


 Tarso-metatarsus, 53

 Tears, 303

 Temporal arterial plexus, 216
   artery, 215
   bone, 29
     petrosal portion, 31
     squamous portion, 30

 Temporalis muscle, 76

 Tendon Achillis, 69

 Tendonal groove, 54

 Tensor patagii brevis, 99
   longus, 99
   tympani, 128

 Teres et infraspinatus muscle, 98
   minor muscle, 103

 Testicles, 175

 Thalamus optici, 289

 Thorax, 41

 Thymus gland, 190

 Thyroid artery, 215
   gland, 190

 Tibialis anticus muscle, 119

 Tissue, osseous, 17

 Toes, 54

 Tongue, 139, 140

 Touch corpuscle, 307

 Trachea, 194

 Trachelo-mastoideus muscle, 85

 Transparent specimens, 350

 Transversales abdominis muscle, 92

 Transverse fissure, 289
   vein, 233

 Transversus peronei, 94

 Trapezius muscle, 97

 Triangularis sterni muscle, 90

 Triceps brachii, 104
   muscle, 104

 Trifacial nerve, 268

 Trochanter, 50

 Trochanteric fossa, 50
   ridge, 50

 Trochlea, femoral, 50

 True joints, 56

 Tuba auditiva, 29, 136

 Tuber cinereum et infundibulum, 289

 Tuberculum costæ, 42

 Tuberositas furcularis, 44
   humeralis, 44
   muscularis, 64
   radii, 46
   scapularis, 44

 Tubuli seminiferi, 176, 318
   uriniferi corticales, 170

 Tunica adventitia, 210
   intima, 210
   media, 210

 Turbinate bones, 34, 193

 Tympanic membrane, 31


 Ulna, 44, 46

 Ulnar nerve, 284

 Umbilical artery, 228

 Umbilicus, 31

 Ureter, 174, 187

 Urinary apparatus, 169
   canals, 170

 Urodeum, 151

 Urogenital system, 169

 Uro-hyal process, 35


 Vagina, 187

 Valve of Vieussens, 290

 Valves of veins, 211

 Vane, 310

 Vas deferens, 175, 178

 Vasa vasorum, 211

 Vastus externus muscle, 113
   internus muscle, 113

 Vaxillum, 310

 Vein or veins, 233
   anterior vertebral, 234
   ascendentes laterales, 242
   basilica, 246
   brachialis, 246
   carotes, 241
   cava sinister, 245
   cavæ, 233
   cephalica posterior, 239
   coccygea, 230
   colli cutineæ, 242
   coracoidea, 244
   cutinea abdominis femoralis, 250
     caudalis, 251
     cruralis, 249
     pubica, 251
   epigastric, 230
   esophageal, 243
   facialis communis, 238
     cutinea, 238
     externa, 235
   femoralis anterior, 250
     interna profunda, 230
   foraminis occipitalis, 240
   fovæ hemispherii cerebelli, 241
   glandularum thyroidearum, 243
   humeri, 245
   hypogastric, 251
   intercostales, 244
   internal mandibular, 237
   intervertebrales lumbalis, 252
     sacrales, 249
   ischiadic, 252
   jugularis, 233
   linguales, 242
   lingualis et hyoides, 238
   longitudinalis, 239
   maxillaris, 235
   metatarsalis dorsalis interna, 249
       profunda, 249
     externa, 249
     plantaris profunda, 249
   occipitalis, 240
     externa, 242
     externus, 240
   of brain cavity, 241
   of dorsal region, 243
   of fore limb, 245
   of head, 235
   of hind limb, 248
   of neck, 242
   of thorax, 244
   of viscera, 252
   ophthalmica, 236
   ovariana, 252
   palpebralis, 238
   petrosus sphenoideus, 240
   pharyngeæ superiores, 238
   poplitealis, 251
   posterior vena cava, 247
     vertebral, 234
   profundus ulnaris, 245
   proventricularis communis, 245
     inferior, 253
   pudenda, 251
   pulmonary, 233
   radialis profunda, 245
   renales, 249
   renalis magna, 252
   retis mirabilis temporalis, 237
   sacrales, 249
   semicircularis, 240
   spermatica, 251
   sternalis, 244
   structure of, 211
   subclavicularis, 233
   subscapularis, 243
   supra-palatina, 236
   suprarenalis externa, 251
     revehentes, 252
   surales, 244
   temporalis, 238
   temporo-sphenoideus, 240
   testiculæ, 252
   thoracica externa, 244
     interna, 244
   tibialis postica, 248
   trachealis, 243
   transversus, 233, 238
   vertebralis lateralis dorsalis, 243

 Venous sinuses, 239
   trunks, 233

 Ventral ligament of oviduct, 188

 Ventricles of heart, 324

 Ventriculus, 143

 Vertebræ, 35
   cervical, 35
   coccygeal, 35
   dorsal, 35, 39
   lumbo-sacral, 35, 39

 Vertebral artery, 215
   column, 35

 Vestibulum, 306

 Villi, 149

 Vitellicle, 321

 Vitelline membrane, 180
   veins, 324, 327

 Vocal apparatus, 195


 Wish bone, 244

 Wolffian duct, 184, 339


 Xanthophyll, 314


 Yolk, 180
   sac, 327


 Zona opaca, 320
   pellucida, 320

 Zygapophyses, 38, 39

 Zygomatic bone, 23, 31, 33
   process, 30

------------------------------------------------------------------------




                          TRANSCRIBER’S NOTES


 1. Silently corrected obvious typographical errors and variations in
      spelling.
 2. Retained archaic, non-standard, and uncertain spellings as printed.
 3. Enclosed italics font in _underscores_.
 4. Enclosed bold font in =equals=.