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  |                       TRANSCRIBER'S NOTES                          |
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  THE
  ARTISTIC ANATOMY OF ANIMALS




  ARTISTIC
  ANATOMY
  OF ANIMALS

  BY ÉDOUARD CUYER, SUPPLEMENTARY
  PROF OF ANATOMY AT THE SCHOOL OF
  FINE ART PARIS, PROF OF ANATOMY
  AT THE SCHOOL OF FINE ART ROUEN

  TRANSLATED & EDITED BY
  GEORGE HAYWOOD
  LECTURER ON ANATOMY AT THE ROYAL
  COLLEGE OF ART SOUTH KENSINGTON

  [Illustration]

  LONDON
  BAILLIÈRE, TINDALL & COX
  8 HENRIETTA ST COVENT GARDEN

  ANNO DOMINI
  MDCCCCV

  ALL RIGHTS
  RESVD




PREFACE


A few lines will suffice to explain why we have compiled the present
volume, to what wants it responds, and what its sphere of usefulness may
possibly embrace.

In our teaching of plastic anatomy, especially at the École des
Beaux-Arts--where, for the past nine years, we have had the very great
honour of supplementing the teaching of our distinguished master,
Mathias Duval, after having been prosector for his course of lectures
since 1881--it is our practice to give, as a complement to the study of
human anatomy, a certain number of lessons on the anatomy of those
animals which artists might be called on to represent.

Now, we were given to understand that the subject treated in our
lectures interested our hearers, so much so that we were not surprised
to learn that a certain number repeatedly expressed a desire to see
these lectures united in book form.

To us this idea was not new; for many years the work in question had
been in course of preparation, and we had collected materials for it,
with the object of filling up a void of which the existence was to be
regretted. But our many engagements prevented us from executing our
project as early as we would have wished. It is this work which we
publish to-day.

[Illustration: FIG. I.--REPRODUCTION OF A SKETCH BY BARYE (COLLECTIONS
OF THE ANATOMICAL MUSEUM OF THE ÉCOLE DES BEAUX-ARTS--HUGUIER MUSEUM).]

Putting aside for a moment the wish expressed by our hearers, we feel
ourselves in duty bound to inquire whether the utility of this
publication is self-evident. Let it be clearly understood that we wish
to express here our opinion on this subject, while putting aside every
personal sentiment of an author.

No one now disputes the value of anatomical studies made in view of
carrying out the artistic representation of man. Nevertheless--for we
must provide against all contingencies--the conviction on this subject
may be more or less absolute; and yet it must possess this character in
an intense degree in order that these studies may be profitable, and
permit the attainment of the goal which is proposed in undertaking them.
It is in this way that we ever strive to train the students whose
studies we direct; not only to admit the value of these studies, but to
be materially and deeply convinced of the fact without any restriction.
Such is the sentiment which we endeavour to create and vigorously
encourage. And we may be permitted to add that we have often been
successful in this direction.

Therefore it is that, at the beginning of our lectures, and in
anticipation of possible objections, we are accustomed to take up the
question of the utility of plastic anatomy. And in so doing, it is in
order to combat at the outset the idea--as mischievous as it is
false--which is sometimes imprudently enunciated, that the possession of
scientific knowledge is likely to tarnish the purity and freshness of
the impressions received by the artist, and to place shackles on the
emotional sincerity of their representation.

[Illustration: FIG. II.--REPRODUCTION OF A SKETCH OF BARYE (COLLECTIONS
OF THE ANATOMICAL MUSEUM OF THE ÉCOLE DES BEAUX-ARTS--HUGUIER MUSEUM).]

It is chiefly by employment of examples that we approach the subject.
These strike the imagination of the student more forcibly, and the
presentation of models of a certain choice, although rough in execution,
is, in our opinion, preferable to considerations of an order possibly
more exalted, but of a character less clearly practical. Let us, then,
ask the question: Those artists whose eminence nobody would dare to
question, did they study anatomy? If the answer be in the affirmative,
we surely cannot permit ourselves to believe that we can dispense with a
similar course. And, as proof of the studies of this class which the
masters have made, we may cite Raphael, Michelangelo, and, above all,
Leonardo da Vinci; and, of the moderns, Géricault. And we may more
clearly define these proofs by an examination of the reproductions of
their anatomical works, chosen from certain of their special
writings.[1]

  [1] Mathias Duval and A. Bical, 'L'anatomie des Maîtres.' Thirty
      plates reproduced from the originals of Leonardo da Vinci,
      Michelangelo, Raphael, Géricault, etc., with letterpress and a
      history of plastic anatomy, Paris, 1890.

      The manuscripts of Leonardo da Vinci of the Royal Library,
      Windsor, 'Anatomy, Foliæ A.,' published by Théodore Sabachnikoff,
      with a French translation, written and annotated by Giovanni
      Piumati, with an introduction by Mathias Duval. Édouard Rouveyre,
      publisher, Paris, 1898.

      Mathias Duval and Édouard Cuyer, 'History of Plastic Anatomy: The
      Masters, their Books, and Anatomical Figures' (Library of
      Instruction of the School of Fine Arts), Paris, 1898.

Accordingly, there is no scope for serious discussion, and it only
remains for us to enunciate the opinion that it is necessary that we
should imitate those masters, and, with a sense of respectful
discipline, follow their example.

Here, with regard to the anatomy of animals, we pursue the same method,
and the example chosen shall be that of Barye. His talent is too far
above all criticism to allow that this example should be refused. The
admiration which the works of this great artist elicit is too
wide-spread for us to remain uninfluenced by the lessons furnished by
his studies. It is sufficient to see the sketches relating to these
studies, and his admirable casts from nature which form part of the
anatomical museum of the École des Beaux-Arts, to be convinced that the
artistic temperament, of which Barye was one of the most brilliant
examples, has nothing to lose by its association with researches the
precision of which might seem likely to check its complete expansion.

[Illustration: FIG. III.--REPRODUCTION OF A SKETCH OF BARYE (COLLECTIONS
OF THE ANATOMICAL MUSEUM OF THE ÉCOLE DES BEAUX-ARTS--HUGUIER MUSEUM).]

In those sketches we find proofs of observation so scrupulous that we
cannot restrain our admiration for the man whose ardent imagination
was voluntarily subjected to the toil of study so profound.

If the example of Barye, with whom we associate the names of other great
modern painters of animals, can determine the conviction which we seek
to produce, we shall be sincerely glad. To contribute to the propagation
of useful ideas, and to see them accepted, gives a feeling of
satisfaction far too legitimate for us to hesitate to say what we should
feel if our hope be realized in this instance.

ÉDOUARD CUYER.

[Illustration: FIG. IV.--REPRODUCTION OF A SKETCH OF BARYE (COLLECTIONS
OF ANATOMICAL MUSEUM OF THE SCHOOL OF FINE ARTS--HUGUIER MUSEUM).]




CONTENTS


  INTRODUCTION

                                                                   PAGE

  GENERALITIES OF COMPARATIVE ANATOMY                                 1


  CHAPTER I

  OSTEOLOGY AND ARTHROLOGY:

  THE TRUNK                                                           4
  THE POSTERIOR LIMBS                                                78
  THE POSTERIOR LIMBS IN SOME ANIMALS                                90
  THE SKULL OF BIRDS                                                127


  CHAPTER II

  MYOLOGY:

  THE MUSCLES OF THE TRUNK                                          131
  MUSCLES OF THE ANTERIOR LIMBS                                     162
  MUSCLES OF THE POSTERIOR LIMBS                                    200
  MUSCLES OF THE HEAD                                               232


  CHAPTER III

  EPIDERMIC PRODUCTS OF THE EXTREMITIES OF THE FORE AND HIND LIMBS  247


  CHAPTER IV

  PROPORTIONS

  PROPORTIONS OF THE HEAD OF THE HORSE                              273


  CHAPTER V

  THE PACES OF THE HORSE                                            282




LIST OF ILLUSTRATIONS


  FIG.                                                             PAGE

    1. A HUMAN SKELETON IN THE ATTITUDE OF A QUADRUPED, TO GIVE A
       GENERAL IDEA OF THE POSITION OF THE BONES IN OTHER
       VERTEBRATES                                                    5
    2. SIZE OF THE ATLAS COMPARED WITH THE TRANSVERSE DIMENSIONS OF
       THE CORRESPONDING PARTS OF THE SKULL IN MAN                    7
    3. SIZE OF THE ATLAS COMPARED WITH THE TRANSVERSE DIMENSIONS OF
       THE CORRESPONDING REGIONS OF THE SKULL IN A DOG                8
    4. LUMBAR VERTEBRÆ OF A QUADRUPED (THE HORSE): SUPERIOR SURFACE   9
    5. A TRANSVERSE SECTION OF THE THORAX OF A MAN PLACED
       VERTICALLY--THAT IS TO SAY, IN THE DIRECTION WHICH IT WOULD
       ASSUME IN A MAN PLACED IN THE ATTITUDE OF A QUADRUPED (A
       DIAGRAMMATIC FIGURE)                                          13
    6. A VERTICAL SECTION OF THE THORAX OF A QUADRUPED
       (DIAGRAMMATIC)                                                14
    7. STERNUM OF A BIRD (THE COCK): LEFT SIDE, EXTERNAL SURFACE     17
    8. ANTERIOR LIMB OF THE BAT: LEFT SIDE, ANTERIOR SURFACE         20
    9. ANTERIOR LIMB OF THE SEAL: LEFT SIDE, EXTERNAL SURFACE        21
   10. SITUATION AND DIRECTION OF THE SCAPULA IN THE HUMAN BEING,
       THE TRUNK BEING HORIZONTAL, AS IN QUADRUPEDS. VERTICAL AND
       TRANSVERSE SECTION OF THE THORAX (DIAGRAMMATIC FIGURE)        22
   11. POSITION AND DIRECTION OF THE SCAPULA IN QUADRUPEDS.
       VERTICAL AND TRANSVERSE SECTION OF THE THORAX (DIAGRAMMATIC
       FIGURE)                                                       22
   12. LEFT SCAPULA OF THE HUMAN BEING, POSTERIOR SURFACE, PLACED
       IN THE POSITION WHICH IT WOULD OCCUPY IN THE SKELETON OF A
       QUADRUPED                                                     23
   13. LEFT SCAPULA OF A HORSE: EXTERNAL SURFACE                     23
   14. VERTICAL AND TRANSVERSE SECTION, AT THE SITE OF THE
       SHOULDERS, OF THE THORAX OF THE HORSE (DIAGRAMMATIC FIGURE)   24
   15. VERTICAL AND TRANSVERSE SECTION, AT THE PLANE OF THE
       SHOULDERS, OF THE THORAX OF THE DOG (DIAGRAMMATIC FIGURE)     24
   16. LEFT CLAVICLE OF THE CAT: SUPERIOR SURFACE (NATURAL SIZE)     26
   17. CLAVICLE OF THE DOG (NATURAL SIZE)                            26
   18. SKELETON OF THE SHOULDER OF A BIRD (VULTURE): ANTERO-
       EXTERNAL VIEW OF THE LEFT SIDE                                27
   19. INFERIOR EXTREMITY OF THE LEFT HUMERUS OF A FELIDÆ (LION)     31
   20. INFERIOR EXTREMITY OF THE LEFT HUMAN HUMERUS, SHOWING THE
       PRESENCE OF A SUPRATROCHLEAR PROCESS                          31
   21. SKELETON OF A BIRD (VULTURE): LEFT SURFACE                    33
   22. THE HUMAN HAND RESTING FOR ITS WHOLE EXTENT ON ITS PALMAR
       SURFACE: LEFT SIDE, EXTERNAL SURFACE                          35
   23. THE HUMAN HAND RESTING ON ITS PHALANGES: LEFT SIDE, EXTERNAL
       SURFACE                                                       36
   24. THE HUMAN HAND RESTING ON THE TIPS OF SOME OF ITS THIRD
       PHALANGES: LEFT SIDE, EXTERNAL VIEW                           36
   25. SUPERIOR EXTREMITY OF THE BONES OF THE HUMAN FOREARM: LEFT
       SIDE, SUPERIOR SURFACE                                        39
   26. SUPERIOR EXTREMITY OF THE BONES OF THE FOREARM OF A DOG:
       LEFT LIMB, SUPERIOR SURFACE                                   39
   27. SUPERIOR EXTREMITY OF THE BONES OF THE FOREARM OF THE HORSE:
       LEFT LIMB, SUPERIOR SURFACE                                   40
   28. INFERIOR EXTREMITY OF THE BONES OF THE FOREARM OF A MAN:
       LEFT SIDE, POSTERIOR SURFACE, POSITION OF SUPINATION          41
   29. INFERIOR EXTREMITY OF THE BONES OF THE FOREARM OF A DOG:
       LEFT SIDE, ANTERIOR SURFACE, NORMAL POSITION--THAT IS, THE
       POSITION OF PRONATION                                         41
   30. INFERIOR EXTREMITY OF THE BONE OF THE FOREARM OF THE HORSE:
       LEFT SIDE, ANTERIOR SURFACE                                   42
   31. SKELETON OF THE SUPERIOR LIMB OF A BIRD (VULTURE): LEFT
       SIDE, EXTERNAL SURFACE                                        47
   32. SUPERIOR LIMB OF THE HUMAN BEING, THE DIFFERENT SEGMENTS
       BEING PLACED IN THE ATTITUDE WHICH THE CORRESPONDING PARTS
       OCCUPY IN BIRDS: LEFT SIDE, EXTERNAL SURFACE                  48
   33. SKELETON OF THE BEAR: LEFT LATERAL SURFACE                    50
   34. SKELETON OF THE DOG: LEFT LATERAL SURFACE                     52
   35. SCAPULA OF THE DOG: LEFT SIDE, EXTERNAL SURFACE               53
   36. LEFT SCAPULA OF THE CAT: EXTERNAL SURFACE                     53
   37. SKELETON OF THE FINGER OF A FELIDE (LION): LEFT SIDE,
       INTERNAL SURFACE                                              57
   38. SKELETON OF THE PIG: LEFT LATERAL SURFACE                     58
   39. SKELETON OF THE OX: LEFT LATERAL SURFACE                      61
   40. SKELETON OF THE HORSE: LEFT LATERAL SURFACE                   64
   41. FLEXION OF THE HUMERUS: RIGHT ANTERIOR LIMB OF THE HORSE,
       EXTERNAL SURFACE (AFTER A CHROMOPHOTOGRAPHIC STUDY BY
       PROFESSOR MAREY)                                              74
   42. EXTENSION OF THE HUMERUS: RIGHT ANTERIOR LIMB OF THE HORSE,
       EXTERNAL SURFACE (AFTER A CHROMOPHOTOGRAPHIC STUDY BY
       PROFESSOR MAREY)                                              74
   43. THE LEFT ILIAC BONE OF THE HUMAN BEING: EXTERNAL SURFACE,
       PLACED IN THE POSITION WHICH IT WOULD OCCUPY IN THE SKELETON
       OF A QUADRUPED                                                79
   44. LEFT ILIAC BONE OF A QUADRUPED (HORSE): EXTERNAL SURFACE      79
   45. PUBIC REGION OF THE PELVIS OF A MARSUPIAL (PHALANGER, FOX)    81
   46. PELVIS OF A BIRD (THE COCK): EXTERNAL SURFACE, LEFT SIDE      82
   47. POSTERIOR LIMB OF THE HORSE PLACED IN THE POSITION WHICH IT
       SHOULD OCCUPY IF THE ANIMAL WERE A PLANTIGRADE: LEFT LIMB,
       EXTERNAL SURFACE                                              89
   48. SKELETON OF THE FOOT OF A BIRD (THE COCK): LEFT SIDE,
       EXTERNAL SURFACE                                              90
   49. PELVIS OF THE DOG, SEEN FROM ABOVE                            91
   50. PELVIS OF A FELIDE (LION), VIEWED FROM ABOVE                  92
   51. PELVIS OF THE OX: SUPERIOR SURFACE                            95
   52. TARSUS OF THE OX: POSTERIOR LEFT LIMB, ANTERO-EXTERNAL
       SURFACE                                                       97
   53. PELVIS OF THE HORSE: SUPERIOR SURFACE                        101
   54. TARSUS OF THE HORSE: LEFT POSTERIOR LIMB, ANTERIOR SURFACE   104
   55. EXTENSION OF THE LEG: RIGHT POSTERIOR LIMB OF THE HORSE,
       EXTERNAL SURFACE (AFTER A CHRONOGRAPHIC STUDY BY PROFESSOR
       MAREY)                                                       107
   56. HUMAN SKULL: MEASURE OF THE FACIAL ANGLE BY THE METHOD OF
       CAMPER. ANGLE BAC = 80°                                      110
   57. SKULL OF THE HORSE: MEASURE OF THE FACIAL ANGLE BY THE
       METHOD OF CAMPER. ANGLE BAC = 13°                            110
   58. SKULL OF ONE OF THE FELIDÆ (JAGUAR): LEFT LATERAL ASPECT     113
   59. SKULL OF THE LION: LEFT LATERAL ASPECT                       113
   60. SKULL OF THE DOG: LEFT LATERAL ASPECT                        115
   61. SKULL OF THE PIG: LEFT LATERAL ASPECT                        117
   62. SKULL OF THE OX: LEFT LATERAL ASPECT                         119
   63. SKULL OF THE HORSE: LEFT LATERAL ASPECT                      121
   64. SKULL OF THE HARE: LEFT LATERAL ASPECT                       123
   65. SKULL OF THE COCK: LEFT LATERAL SURFACE                      128
   66. MYOLOGY OF THE HORSE: ANTERIOR ASPECT OF THE TRUNK           132
   67. MYOLOGY OF THE HORSE: INFERIOR ASPECT OF THE TRUNK           135
   68. MYOLOGY OF THE DOG: SUPERFICIAL LAYER OF MUSCLES             141
   69. MYOLOGY OF THE OX: SUPERFICIAL LAYER OF MUSCLES              143
   70. MYOLOGY OF THE HORSE: SUPERFICIAL LAYER OF MUSCLES           146
   71. MYOLOGY OF THE HORSE: PANNICULUS MUSCLE OF THE TRUNK         148
   72. MYOLOGY OF THE HORSE--SHOULDER AND ARM: LEFT SIDE, EXTERNAL
       SURFACE                                                      166
   73. MYOLOGY OF THE DOG: LEFT ANTERIOR LIMB, EXTERNAL ASPECT      178
   74. MYOLOGY OF THE OX: LEFT ANTERIOR LIMB, EXTERNAL ASPECT       180
   75. MYOLOGY OF THE HORSE: LEFT ANTERIOR LIMB, EXTERNAL ASPECT    182
   76. MYOLOGY OF THE DOG: LEFT ANTERIOR LIMB, INTERNAL ASPECT      190
   77. MYOLOGY OF THE HORSE: ANTERIOR LIMB, LEFT SIDE, INTERNAL
       ASPECT                                                       192
   78. LEFT ANTERIOR LIMB OF THE HORSE: INTERNAL ASPECT             194
   79. LEFT ANTERIOR LIMB OF THE HORSE: EXTERNAL ASPECT             196
   80. LEFT ANTERIOR LIMB OF THE HORSE: EXTERNAL ASPECT             196
   81. DIAGRAM OF THE POSTERIOR PART OF A TRANSVERSE SECTION
       PASSING THROUGH THE MIDDLE OF THE LEFT FORE-LIMB OF THE DOG:
       SURFACE OF THE INFERIOR SEGMENT OF THE SECTION               198
   82. DIAGRAM OF A HORIZONTAL SECTION OF THE MIDDLE OF THE FOREARM
       OF THE LEFT LEG OF THE HORSE: SURFACE OF THE INTERIOR
       SEGMENT OF THE SECTION                                       198
   83. MYOLOGY OF THE HORSE: THE ANTERIOR TIBIAL MUSCLE (FLEXOR OF
       THE METATARSUS), LEFT LEG, ANTERIOR VIEW                     214
   84. MYOLOGY OF THE DOG: LEFT HIND-LIMB, EXTERNAL ASPECT          216
   85. MYOLOGY OF THE OX: LEFT LEG, EXTERNAL ASPECT                 218
   86. MYOLOGY OF THE HORSE: LEFT HIND-LIMB, EXTERNAL ASPECT        220
   87. MYOLOGY OF THE DOG: LEFT HIND-LIMB, INTERNAL ASPECT          222
   88. MYOLOGY OF THE HORSE: LEFT HIND-LEG, INTERNAL ASPECT         223
   89. MYOLOGY OF THE DOG: MASTICATORY MUSCLES (A DEEPER DISSECTION
       THAN THAT SHOWN IN FIG. 90)                                  233
   90. MYOLOGY OF THE DOG: MUSCLES OF THE HEAD                      235
   91. MYOLOGY OF THE OX: MUSCLES OF THE HEAD                       237
   92. MYOLOGY OF THE HORSE: MUSCLES OF THE HEAD                    239
   93. CLAW OF THE DOG: INFERIOR SURFACE                            249
   94. LEFT HAND OF THE DOG: INFERIOR SURFACE, PLANTAR TUBERCLES    249
   95. VERTICAL ANTERO-POSTERIOR SECTION OF THE FOOT OF A HORSE     250
   96. THIRD PHALANX OF THE HORSE: LEFT ANTERIOR LIMB, EXTERNAL
       SURFACE                                                      251
   97. LEFT ANTERIOR FOOT OF THE HORSE: ANTERIOR ASPECT             253
   98. LEFT ANTERIOR FOOT OF THE HORSE: EXTERNAL ASPECT             254
   99. VERTICAL AND TRANSVERSE SECTION OF A LEFT HUMAN FOOT:
       OUTLINE OF THE SURFACE OF THE POSTERIOR SEGMENT OF THIS
       SECTION (DIAGRAMMATIC FIGURE)                                255
  100. INFERIOR SURFACE OF A FORE-HOOF OF THE HORSE: LEFT SIDE      256
  101. THIRD PHALANX OF THE HORSE: LEFT ANTERIOR LIMB, INFERIOR
       VIEW                                                         257
  102. THIRD PHALANX OF THE HORSE: LEFT POSTERIOR LIMB, INFERIOR
       VIEW                                                         257
  103. INFERIOR SURFACE OF A HIND-HOOF OF A HORSE: LEFT SIDE        258
  104. LEFT POSTERIOR FOOT OF A HORSE: EXTERNAL ASPECT              259
  105. FOOT OF THE OX: LEFT SIDE, ANTERO-EXTERNAL VIEW              260
  106. THE PROPORTIONS OF THE HORSE (AFTER BOURGELAT)               265
  107. PROPORTIONS OF THE HORSE (AFTER COLONEL DUHOUSSET)           270
  108. PROPORTIONS OF THE HEAD OF THE HORSE, VIEWED IN PROFILE
       (AFTER COLONEL DUHOUSSET)                                    274
  109. THE SAME DESIGN AS THAT OF FIG. 108, ON WHICH WE HAVE
       INDICATED, BY SIMILAR LINES, THE PRINCIPAL CORRESPONDING
       MEASUREMENTS                                                 275
  110. PROPORTIONS OF THE HEAD OF THE HORSE, SEEN FROM THE FRONT
       (AFTER COLONEL DUHOUSSET)                                    276
  111. THE SAME FIGURE AS FIG. 110, ON WHICH WE HAVE MARKED, BY
       SIMILAR LINES, THE PRINCIPAL MEASUREMENTS WHICH CORRESPOND
       THERETO                                                      277
  112. HORSE OF WHICH THE LENGTH CONTAINS MORE THAN TWO AND A HALF
       TIMES THAT OF THE HEAD, AND OF WHICH THIS DIMENSION (A, B)
       EXCEEDS THE HEIGHT                                           279
  113. HORSE OF WHICH THE LENGTH CONTAINS MORE THAN TWO AND A HALF
       TIMES THAT OF THE HEAD, AND OF WHICH THIS DIMENSION (A, B)
       EXCEEDS THE HEIGHT                                           280
  114. HORSE OF WHICH THE LENGTH CONTAINS MORE THAN TWO AND A HALF
       TIMES THAT OF THE HEAD, AND OF WHICH THIS DIMENSION (A, B)
       IS INFERIOR TO THE HEIGHT                                    281
  115. EXPERIMENTAL SHOES, INTENDED TO RECORD THE PRESSURE OF THE
       FOOT ON THE GROUND                                           284
  116. RUNNER FURNISHED WITH THE EXPLORATORY AND REGISTERING
       APPARATUS OF THE VARIOUS PACES                               285
  117. TRACING OF THE RUNNING OF A MAN (AFTER PROFESSOR MAREY)      286
  118. NOTATION OF A TRACING OF THE RUNNING OF A MAN (AFTER
       PROFESSOR MAREY)                                             287
  119. NOTATION OF VARIOUS MODES OF PROGRESSION OF A MAN (AFTER
       PROFESSOR MAREY)                                             287
  120. SWING OF THE RAISED ANTERIOR LIMB (AFTER G. COLIN)           289
  121. SWING OF THE ANTERIOR LIMB ON THE POINT OF PRESSURE (AFTER
       G. COLIN)                                                    290
  122. POSTERIOR LIMB, GIVING THE IMPULSE (AFTER G. COLIN)          291
  123. NOTATION OF THE AMBLING GAIT IN THE HORSE (AFTER PROFESSOR
       MAREY)                                                       292
  124. THE AMBLE: RIGHT LATERAL PRESSURE                            293
  125. NOTATION OF THE GAIT OF THE TROT IN A HORSE (AFTER PROFESSOR
       MAREY)                                                       294
  126. THE TROT: RIGHT DIAGONAL PRESSURE                            295
  127. THE TROT: TIME OF SUSPENSION                                 295
  128. NOTATION OF THE PACE OF STEPPING IN THE HORSE (AFTER
       PROFESSOR MAREY)                                             296
  129. THE STEP: RIGHT LATERAL PRESSURE                             297
  130. THE STEP: RIGHT DIAGONAL PRESSURE                            297
  131. THE GALLOP: FIRST PERIOD                                     298
  132. THE GALLOP: SECOND PERIOD                                    298
  133. THE GALLOP: THIRD PERIOD                                     299
  134. THE GALLOP: TIME OF SUSPENSION                               299
  135. NOTATION OF THE GALLOP DIVIDED INTO THREE PERIODS OF TIME
       (AFTER PROFESSOR MAREY)                                      300
  136. NOTATION OF THE GALLOP OF FOUR PERIODS IN THE HORSE (AFTER
       PROFESSOR MAREY)                                             300
  137. LEAP OF THE HARE (AFTER G. COLIN)                            301
  138. THE LEAP                                                     302
  139. THE LEAP                                                     302
  140. THE LEAP                                                     303
  141. THE LEAP                                                     303
  142. THE LEAP                                                     305
  143. THE LEAP                                                     305




THE ARTISTIC ANATOMY OF ANIMALS




INTRODUCTION

GENERALITIES OF COMPARATIVE ANATOMY


Of the animals by which we are surrounded, there are some which,
occupying a place in our lives by reason of their natural endowments,
are frequently represented in the works of artists--either as
accompanying man in his work or in his amusements, or as intended to
occupy the whole interest of the composition.

The necessity of knowing, from an artistic point of view, the structure
of the human body makes clear the importance we attach, from the same
point of view, to the study of the anatomy of animals--that is, the
study of comparative anatomy. The name employed to designate this branch
of anatomy shows that the object of this science is the study of the
relative position and form which each region presents in all organized
beings, taking for comparison the corresponding regions in man. The head
in animals compared with the human head; the trunk and limbs compared to
the trunk and limbs of the human being--this is the analysis we
undertake, and the plan of the subject we are about to commence.

Our intention being, as we have just said, the comparison of the
structure of animals with that of man, should we describe the anatomy of
the human being in the pages which follow? We do not think so. Plastic
human anatomy having been previously studied in special works,[2] we
take it for granted that these have been studied before undertaking the
subject of comparative anatomy. We will therefore not occupy time with
the elementary facts relative to the skeleton and the superficial layer
of muscles. We will not dilate on the division of the bones into long,
short, large, single, paired, etc. All these preliminary elements we
shall suppose to have been already studied.

  [2] Mathias Duval, 'Précis of Anatomy for the Use of Artists': Paris,
      1881. 'Artistic Anatomy of the Human Body,' third edition, plates
      by Dr. Fau, text with figures by Édouard Cuyer: Paris, 1896.
      'Artistic Anatomy of Man,' by J. C. L. Sparkes, second edition,
      text with 50 plates: Baillière, Tindall and Cox, London, 1900.

This being granted, it is, nevertheless, necessary to take a rapid
bird's-eye view of organized beings, and to recall the terms used in
their classification.

Animals are primarily classed in great divisions, based on the general
characters which differentiate them most. These divisions, or
_branches_, allow of their being so grouped that in each of them we find
united the individuals whose general structure is uniform; and under the
name of vertebrates are included man and the animals with which our
studies will be occupied. The vertebrates, as the name indicates, are
recognised by the presence of an interior skeleton formed by a central
axis, the vertebral column, round which the other parts of the skeleton
are arranged.

The vertebrate branch is divided into classes: fishes, amphibians or
batrachians, reptiles, birds, and mammals.

The mammals--from the Latin _mamma_, a breast--are characterized by the
presence of breasts designed for the alimentation of their young. Their
bodies are covered with hair, hence the name _pilifères_ proposed by
Blainville; and, notwithstanding that in some individuals the hairs are
few, the character is sufficient to distinguish them from all other
vertebrates.

We find united in this class animals which, at first, seem out of place,
such as the whale and the bat; and, from their external appearance
alone, the former would appear to belong to the fishes, and the latter
to birds. Yet, on studying their structure, we find that, not only do
these animals merit a place in the class which they occupy, because they
possess the distinctive characters of mammals; but, still further, their
internal structure is analogous to that of man and of the other
individuals of this class.

Notwithstanding this similarity of structure, the whale is not without
some points of difference from its neighbours the horse and the dog;
therefore, in order to place each of these animals in a position
suitable to it, mammals are divided into secondary groups called
_orders_. The first of these orders includes, under the name _primates_,
man and apes. The latter contain animals which approach birds in certain
characters of their organism, forming a link between the latter and
mammals.

We find, in studying the regions of the body in some of the vertebrates,
that, while they present differences from the corresponding regions of
the human body, they also offer most striking analogies. We can, for
example, recognise the upper limb of man in the anterior one of
quadrupeds, in the wing of the bat, in the paddle of the seal, etc. It
is, so to speak, those variations of a great plan which give such a
charm to the study of comparative anatomy.

The division of classes into orders, which we have just mentioned,
being still too general, it was found necessary to establish
subdivisions--more and more specialized--to which the names _families_,
_genera_, _species_, and _varieties_ were given.




CHAPTER I

OSTEOLOGY AND ARTHROLOGY


THE TRUNK

The Vertebral Column

We commence the study of the skeleton with a description of the trunk.

The trunk being, in quadrupeds, horizontal in direction (Fig. 1), the
two regions of which it consists occupy, for this reason, the following
positions: the thorax occupies the anterior part, the abdomen is placed
behind it; the vertebral column is horizontal, and is situated at the
superior aspect of the trunk; it projects beyond the latter: anteriorly,
to articulate with the skull; and, posteriorly, to form the skeleton of
the tail, or caudal appendix.

The number of the vertebræ is not the same in all mammalia. Of the
several regions of the vertebral column, the cervical shows the greatest
uniformity in the number of the vertebræ of which it consists, with but
two exceptions (eight or nine in the three-toed sloth, and six in the
manatee); we always find seven cervical vertebræ, whatever the length of
the neck of the animal. There are no more than seven vertebræ in the
long neck of the giraffe, but they are very long ones; and not less than
seven in the very short neck of the dolphin, in which they are reduced
to mere plates of bone not thicker than sheets of cardboard. If the
cervical region presents uniformity in the number of its bones, it is
not so with the other regions of the column.

The following table shows their classification in some animals:

VERTEBRÆ.

  +------------+-----------+---------+---------+
  |            | Cervical. | Dorsal. | Lumbar. |
  +------------+-----------+---------+---------+
  | Bear       |    7      |    14   |    6    |
  | Dog        |    7      |    13   |    7    |
  | Cat        |    7      |    13   |    7    |
  | Rabbit     |    7      |    12   |    7    |
  | Pig        |    7      |    14   |  6 or 7 |
  | Horse      |    7      |    18   |  6 or 5 |
  | Ass        |    7      |    18   |    5    |
  | Camel      |    7      |    12   |    7    |
  | Giraffe    |    7      |    14   |    5    |
  | Ox         |    7      |    13   |    6    |
  | Sheep      |    7      |    13   |    6    |
  +------------+-----------+---------+---------+

[Illustration: FIG. 1.--A HUMAN SKELETON IN THE ATTITUDE OF A QUADRUPED.
TO GIVE A GENERAL IDEA OF THE POSITION OF THE BONES IN OTHER
VERTEBRATES.]

It is worthy of notice that in birds the number of the cervical vertebræ
is not constant, as in mammals; they are more numerous than the dorsal.
These latter are almost always joined to one another by a fusion of
their spinous processes; the two or three last vertebræ are similarly
united to the iliac bones, between which they are fixed. The dorsal
vertebræ thus form one piece, which gives solidity to the trunk, and
provides a base of support to the wings, for the movements of flying.
There are, so to speak, no lumbar vertebræ, the bones of that region,
which cannot be differentiated from the sacrum, having coalesced with
the bones of the pelvis.

VERTEBRÆ.

  +------------------+-----------+---------+
  |                  | Cervical. | Dorsal. |
  +------------------+-----------+---------+
  | Vulture          |    15     |    7    |
  | Eagle            |    13     |    9    |
  | Cock             |    14     |    7    |
  | Ostrich          |    18     |    9    |
  | Swan             |    23     |   10    |
  | Goose            |    18     |    9    |
  | Duck             |    15     |    9    |
  +------------------+-----------+---------+

In reptiles, the relation between the number of the cervical vertebræ
and that of the dorsal is very variable; some serpents are devoid of
cervical vertebræ, having only dorsal ones--that is, vertebræ carrying
well-developed ribs.

VERTEBRÆ.

  +-------------------+-----------+---------+---------+
  |                   | Cervical. | Dorsal. | Lumbar. |
  +-------------------+-----------+---------+---------+
  | Crocodile         |    7      |    14   |    3    |
  | Caiman            |    7      |    12   |    5    |
  | Boa               |    3      |   248   |    0    |
  | Python            |    0      |   320   |    0    |
  | Viper             |    2      |   145   |    0    |
  +-------------------+-----------+---------+---------+

Regarding the direction of the vertebral column in animals, in which the
trunk is not vertical, it is evident that the spinous processes point
upward, and that in comparing them with those of man they must be
arranged so that the superior surface of the human vertebra will
correspond to the anterior surface of that of the quadruped. Of the
cervical vertebræ, the atlas and axis call for special notice. Apropos
of the atlas, we find that it, in the human being, is narrower than the
corresponding parts of the skull, and is therefore hidden under the base
of the cranium (Fig. 2); in quadrupeds its width is equal to that of the
skull, and sometimes exceeds, because of the great development of its
wing-shaped transverse processes, that of the neighbouring parts of the
head (Fig. 3). On this account those transverse processes often project
under the skin of the lateral surfaces of the upper part of the neck.

[Illustration: FIG. 2.--SIZE OF THE ATLAS COMPARED WITH THE TRANSVERSE
DIMENSIONS OF THE CORRESPONDING PARTS OF THE SKULL IN MAN.

1, Atlas; 2, mastoid process; 3, external occipital protuberance; 4,
inferior maxilla.]

The axis is furnished on its anterior surface with the odontoid process,
which articulates with the anterior (or inferior) arch of the atlas,
according to the direction of the neck. The spinous process, flattened
from without inwards, is more or less pointed; it is elongated from
before backwards, so as partly to overlap the atlas and the third
cervical vertebra.

We find that this process overlaps less and less the neighbouring
vertebræ when we examine in succession the bear, the cat, the dog, the
ox, and the horse. With regard to the other vertebræ of this region,
they diminish in width from the second to the seventh; and, in some
animals, the anterior surface of the body presents a tubercle which
articulates with a cavity hollowed in the posterior surface of that of
the vertebra before it; this feature dwindles away in the dorsal and
lumbar regions.

The spinous process, slightly developed in the third cervical vertebra,
gradually increases in size to the seventh, the spinous process of
which, long and pointed, well deserves the name of _the prominent_ which
is bestowed on it; but it should not be forgotten that the spinous
process of the axis is equally developed.

[Illustration: FIG. 3.--SIZE OF THE ATLAS COMPARED WITH THE TRANSVERSE
DIMENSIONS OF THE CORRESPONDING REGIONS OF THE SKULL IN A DOG.

1, Atlas; 2, zygomatic arch; 3, external occipital protuberance; 4,
inferior maxilla.]

On the inferior surface of the body of each of the vertebræ is found a
prominent crest, especially well marked at the posterior part; this
crest is but slightly developed in the bear and in the cat tribe, and is
not found in swine.

The transverse processes of the cervical vertebræ, from their relation
to the trachea, are known as the _tracheal processes_.

The most marked characteristic of the dorsal vertebræ is furnished by
the spinous processes. They are long and narrow. As a rule, the spinous
processes of the foremost dorsal vertebræ are the most developed and
are directed obliquely upwards and backwards. As we approach the last
vertebræ of this region, the processes become shorter and tend to become
vertical, and the last ones are even, in some cases, directed upwards
and forwards; this disposition is well marked in the dog and the cat. In
the cetaceans, on the contrary, the length of the spinous processes
increases from the first to the last.

[Illustration: FIG. 4.--LUMBAR VERTEBRÆ OF A QUADRUPED (THE HORSE):
SUPERIOR SURFACE.

1, Spinous process; 2, anterior articular process and transverse process
of the first lumbar vertebra of the left side; 3, costiform process.]

In the horse the spinous processes of the first dorsal vertebræ produce
the prominence at the anterior limit of the trunk, where the mane ends,
which is known as the _withers_.

The lumbar vertebræ are thicker than the preceding; they are known by
their short and latterly-flattened spinous processes, and still more
readily by their transverse processes, which, as they are evidently
atrophied ribs, it is more accurate to denominate costiform processes
(Fig. 4). These are long, flattened from above downwards, and directed
outwards and forwards.

The true transverse processes are represented by tubercles situated on
the superior borders of the articular processes of each of the vertebræ
of the lumbar region. Apropos of these different osseous processes, we
are reminded that they are also present in the human skeleton.

In the horse the costiform processes of the fifth and sixth lumbar
vertebræ articulate, and are sometimes ankylosed, one with the other;
the terminal ones articulate with the base of the sacrum. Sometimes the
processes of the fourth and fifth are thus related; this is the case in
the figure (4) given; here the costiform processes of the fourth and
fifth vertebræ articulate, and the two terminal ones have coalesced.

In the ox, the same processes are more developed than in the horse;
their summits elevating the skin, produce, especially in animals which
have not much flesh, prominences which limit the flanks in the superior
aspect. The costiform processes of the last lumbar vertebræ are separate
from each other; those of the latter are not in contact with the sacrum.

=The Sacrum.=[3]--This bone, single and median, is formed by the mutual
coalescence of several vertebræ, which vary in number according to the
species observed.

  [3] In human anatomy, the sacrum and the coccyx are studied as part of
      the pelvis; we, therefore, in the study of the artistic anatomy of
      man, study these bones with the bones of the lower limbs. Here we
      do not follow this plan. In animals the sacrum and the coccyx, as
      a matter of fact, clearly continue the superior border of the
      skeleton of the trunk; hence we study them with the vertebral
      column.

_Vertebræ Constituting the Sacrum._--Bears, 5; dogs, 3; cats, 3;
rabbits, 4; swine, 4; horses, 5; camels, 4; oxen, 5; sheep, 4.

The sacrum is situated between the two iliac bones; with which it
articulates, and contributes to the formation of the pelvis. It is
obliquely placed, from before backwards, and from below upwards;
immediately behind the lumbar section of the vertebral column; and is
continued by the coccygeal vertebræ, which form the skeleton of the
tail.

It is triangular in outline, and is generally more narrow in proportion
than in the human being. All things considered, it is more large and
massive, and of greater density, in species which sometimes assume the
upright posture, rather than in those which cannot assume that
attitude; for example, the sacrum of the ape, of the bear, of the dog,
and of the opossum are proportionately larger than those of the
horse.[4]

  [4] This is particularly striking only in those portions of the sacrum
      that are not in relation with the other bones of the pelvis. We
      think that the general form of this bone depends on the mode of
      its connexions with the iliac bones and the extent of the
      articular surfaces by which it is in contact with the latter.

Its superior surface presents a crest, formed by the fusion of the
spinous processes of the vertebræ which form it. In certain species
these processes are attached only by their bases, and are separated from
each other superiorly. In the pig they are wholly wanting.

=The Coccygeal Vertebræ.=--These vertebræ, few in number (and sometimes
ankylosed) in the human being, form in the latter a small series, the
coccyx; which is inclined forwards, that is to say, towards the interior
of the pelvis. In quadrupeds, on the contrary, their number is large;
they are not ankylosed, and they form the skeleton of the caudal
appendix.

The first coccygeal vertebræ--that is, those which are next the
sacrum--present characters which are common to those of other regions:
they have a body, a foramen, and processes. As we trace them backwards,
these characters become gradually effaced; and they become little more
than small osseous cylinders simply expanded at their extremities.


Direction and Form of the Spinal Column

The curves of the vertebral column are, in quadrupeds, slightly
different from those which characterize the human spine. First, instead
of their being, as in the latter, curves in the antero-posterior aspect,
because of the general attitude of the body, they are turned in the
supero-inferior direction.

The cervical region is not a single curve, as in the human being. It
presents two: one superior, with its convexity looking upwards; the
other inferior, the convexity of which is turned downwards. This
arrangement reminds one of that of a console.

The dorsal and lumbar regions are placed in a single curved line, more
or less concave downwards; so that in the lumbar region there is no
curve analogous to that which exists in man; a form which, in the
latter, is due to the biped attitude--that is to say, the vertical
position of the trunk. Briefly, there is in quadrupeds one dorso-lumbar
curve; and not both a dorsal and a lumbar, with convexities in opposite
directions.

At the extremity of the dorso-lumbar region is the sacrum and the caudal
appendix, which describe a curve of which the concavity is directed
downwards and forwards.

It is necessary to point out that it is not the curves of the three
anterior portions of the spinal column which determine the form of the
superior border of the neck and shoulders, and of the same part of the
trunk. For the first portion, there is a ligament which surmounts the
cervical region, and substitutes its modelling influence for that of the
vertebræ. It is the _superior cervical ligament_, which arises from the
spinous process of the first cervical vertebræ, and is inserted into the
external occipital protuberance on the upper part of the posterior
surface of the skull. The summits of the spinous processes of the
vertebræ alone give form to the superior median border of the trunk. In
this connection we here repeat that it is not the general curvature of
the vertebral column which produces the withers, but the great length of
the spinous process of the first vertebræ of the dorsal region.


The Thorax

The dorsal vertebræ form the posterior limit in man, and superior in
quadrupeds, of the region of the trunk known as the _thorax_. A single
bone, the sternum, is situated at the aspect opposite; the ribs bound
the thorax on its sides.

In its general outlines the thorax in quadrupeds resembles that
of man--that is to say, that, as in the latter, the anterior
portion--superior in the human being--is narrower than the part
opposite. But the progressive widening takes place in a more regular and
continuous fashion, so that it presents a more definitely conical
outline. This purely conical form is nevertheless found in the human
species, but only during infancy; the inferior portion of the thoracic
cage being then widely expanded, because of the development of the
abdominal viscera, which at that period are relatively large.

But the proportionate measurements of the thorax are different. Indeed,
we may recall that in man the thorax is flattened from before backwards,
so that the distance between the sternum and the vertebral column is
shorter than the distance from the rib of one side to the corresponding
one of the opposite side (Fig. 5). In animals, on the contrary, it is
flattened laterally. Its vertical diameter--measured from the sternum to
the vertebral column--is greater than the transverse measurement (Fig.
6).

[Illustration: FIG. 5.--A TRANSVERSE SECTION OF THE THORAX OF A MAN
PLACED VERTICALLY--THAT IS TO SAY, IN THE DIRECTION WHICH IT WOULD
ASSUME IN A MAN PLACED IN THE ATTITUDE OF A QUADRUPED (A DIAGRAMMATIC
FIGURE).

1, Dorsal vertebra; 2, sternal region; 3, costal region of one side; 3´,
costal region of the other side.]

From this results a peculiar arrangement of the muscles that we are able
to bring directly into prominence, which presents points of interest
from the point of view of the contraction of the subcutaneous layer.
Indeed, in man the region occupied by the pectorals is very broad; it is
a wide surface turned directly forward. In quadrupeds, this region of
the pectorals is narrowed. It is not spread out, as in the preceding
instances; and the appearance it presents is explained by the fact that
the thorax is compressed laterally. If we examine the thorax on one of
its lateral surfaces, the muscles, on the contrary, are more extended.
We see the contour of the vertebral column, and the median part of the
abdomen; and, especially in the horse, between the great dorsal and the
great oblique of the abdomen, we find a large space, in which the ribs,
with the intercostals which join them, are uncovered; the muscles in
question separate the one from the other, under the influence, it would
seem, of the great dimensions of the lateral wall of the thorax.

[Illustration: FIG. 6.--A VERTICAL SECTION OF THE THORAX OF A QUADRUPED
(DIAGRAMMATIC).

1, Fifth dorsal vertebra; 2, sternal region; 3, costal region of one
side; 3´, costal region of the opposite side.]

=The Sternum.=--The sternum is, in quadrupeds, directed obliquely
downwards and backwards; its form varies in different species. In the
carnivora, it consists of eight bones, irregularly cylindrical in form,
being slightly flattened from within outwards, and thickened at their
extremities. They remain separate, and this contributes elasticity and
flexibility to the thorax. The first nine costal cartilages articulate
directly with the sternum. The first of these cartilages articulates
with a nodule situated a little above the middle of the first bone of
the sternum.

In the horse the sternum is flattened laterally in its anterior portion,
and from above downwards in its posterior half. The six bones which
form the sternum are connected by cartilage. The keel-shaped piece,
situated in front of the sternum, is also cartilaginous. This process,
but slightly marked posteriorly, becomes more and more prominent in
front, and terminates at its anterior extremity by a prolongation,
slightly curved backwards, which projects for some centimetres beyond
the cavity in which the first costal cartilage is received. This process
is known as the _tracheal process_, or _rostral cartilage_. The
posterior extremity of the sternum, flattened from above downwards, ends
in a cartilaginous plate; concave superiorly, and convex inferiorly:
this is the abdominal prolongation, or _xiphoid appendix_.

In the ox, the sternum is formed of two distinct bones, which are united
by an articulation. One, the anterior, is short, and forms the first
portion of the sternum; it is slightly flattened from side to side, and
vertical in direction. The other, the posterior, is longer, and is
formed by the fusion of several small bones; it is placed horizontally,
and is flattened from above downwards. At the level of articulation of
these two portions, and because of their different directions, the bone
is bent. This bend occurs at the point of articulation of the second
costal cartilage. On the superior border of the anterior segment the
cartilage of the first rib is articulated. The xiphoid appendix, which
is cartilaginous, is attached to the extremity of a long process of the
last bone of the sternum.

The shape of the anterior extremity of the sternum is influenced by the
presence or absence of clavicles. We have seen that in some quadrupeds
the clavicles are wanting. In the first case, this extremity is large,
and approaches in shape to the corresponding part of the human sternum,
which is so clearly designed to give a point of support to the anterior
bone of the shoulder. In the second, on the contrary, this extremity is
narrow.

The sternum in birds is very different from that in mammalia, which we
have been studying. It varies greatly in extent and shape, under the
influence of certain conditions. To understand the cause of these
variations it is necessary to remember that in man (as, indeed, in other
animals; but the example of man, for that which follows, will be more
striking, on account of the mobility of his upper limbs) the sternum
gives origin to the pectoral muscles, and that these muscles are
inserted into other parts of the thoracic limbs, designed by their
contraction to draw the arms downwards, forwards, and inwards--that is,
when these are in a state of abduction and in a horizontal direction,
they draw them towards the anterior surface of the thorax and downwards.
Now, this movement is similar to that made by birds during flight. It is
necessary to add that, in the latter case, the more the displacement of
the upper limbs has of force and extent, the more the pectoral muscles
are developed.

For these reasons, birds, in which, during flight, the movements of the
thoracic limbs--the wings--are necessarily energetic, present a great
development of the pectoral muscles; having consequently, because an
extent of surface for the origin of the muscles commensurate with their
development is necessary, a very large and peculiarly shaped sternum
(Figs. 18, 6; and 21, 6). Indeed, not only is the sternum large, but,
further, in order to form a deeper surface, proportionately adapted to
the muscles which arise from and cover it, its anterior surface
presents, in the median line, a prominent crest known as the _keel_.
This prominence forms two lateral fossæ. We cite as examples, the
sternum of the eagle, the vulture, the falcon, and the hawk.

All birds are not, however, equally adapted to flight, for in the
domestic cock, which flies but a short distance, and badly, the sternum
is less developed (Fig. 7); it is also diminished by slots, which
diminish its surface. These slots, two on each side, are called from
their position the internal and external slots. They are bounded by
narrow, elongated, bony processes, an internal and an external; the
expanded lower extremity of the latter overlaps the last inferior ribs
(see p. 19). The part of the external border which surmounts this
external process is hollowed out into grooves, which receive the
inferior ribs, and terminates superiorly in an osseous projection known
as _the costal prominence_.

In the ostrich, the cassowary, and the apteryx, which run, but do not
fly, the sternum has the form of a plate of bone slightly convex, but
without a keel.

[Illustration: FIG. 7.--STERNUM OF A BIRD (THE COCK): LEFT SIDE,
EXTERNAL SURFACE.

1, Keel; 2, internal slot; 3, external slot; 4, internal process; 5,
external process; 6, inferior ribs; 7, costal process; 8, surface for
articulation with the coracoid bone.]

The shape of the sternum, correlated to the faculty of flight (or of
swimming; apropos of which we may cite the penguin, of which the
rudimentary wings resemble fins, and perform their functions only), or
the absence of this faculty, has furnished the division of birds into
two groups. In one are included, under the name _Carinates_ (_carina_,
keel), those in which the sternum is provided with a keel; in the other
division are those in which the sternum is not furnished with one. These
latter, on account of their unique mode of progression, are more nearly
allied to the mammals.

The keel is developed in flying mammals (bats).

=Ribs and Costal Cartilages.=--There are on each side of the thorax as
many ribs as there are dorsal vertebræ. In animals, as in man, the ribs
which articulate with the sternum by their cartilages are called _true_,
or _sternal_ ribs; those whose cartilages do not articulate with the
sternum are called _false_, or _asternal_. The longer ribs are those
situated in the middle region of the thorax.

The ribs are directed obliquely downwards and backwards, and this
obliquity is more marked in the posterior ones than in the anterior.
They are, however, less oblique than in the human being; what proves
this is that the first rib in man is oblique, while in quadrupeds it is
vertical.

The curvature of the ribs is less pronounced in quadrupeds than in the
human being, but this is not equal in all animals. The ribs of the bear
are more curved than those of the dog; the latter has ribs more curved
than those of the horse.

Each rib, at its vertebral extremity, presents, from within outwards, a
wedge-shaped head for articulation with two dorsal vertebræ, a neck, and
a tuberosity. External to the tubercle are found some rough impressions,
for muscular attachments, which correspond to the angle of the human
rib.

In the following table, we give the number and classification of the
ribs of some animals:

NUMBER OF THE RIBS ON EACH SIDE OF THE THORAX.

                             Sternal.    Asternal.
  Bear       14  divided into   9    and     5
  Dog        13     "      "    9     "      4
  Cat        13     "      "    9     "      4
  Rabbit     12     "      "    7     "      5
  Pig        14     "      "    7     "      7
  Horse      18     "      "    8     "     10
  Camel      12     "      "    8     "      4
  Ox         13     "      "    8     "      5
  Sheep      13     "      "    8     "      5

The costal cartilages, by which the first ribs are united to the sternum
(sternal ribs), whilst the latter are united one to the other without
being directly connected with the sternum (asternal ribs), are, as a
rule, in quadrupeds, directed obliquely downwards, forwards, and
inwards; each forms, with the rib to which it belongs, an obtuse angle
more or less open anteriorly. Their length is proportionate to that of
the ribs. The cartilages, which are continued from the asternal ribs,
unite and form the borders, directed obliquely downwards and forwards,
of the fossa which is found at the inferior and posterior part of the
thorax, and which forms the lateral limits of the epigastric region. In
the dog and cat the ribs are thick and almost cylindrical; the costal
cartilages are thicker at the margin of the sternum than at their costal
extremity. In the ox, the ribs are flattened laterally and are very
broad, the more so as we examine a portion further from the vertebral
column. From the second to the twelfth they are quadrangular in the
superior fourth, and thicker than in the rest of their extent. The first
costal cartilage is vertical; the following ones are progressively more
oblique in a direction downwards and forwards. The four or five
cartilages which succeed the first unite with slight obliquity to the
sternum; their union with that bone gives the impression of a very
strong, well-knit apparatus. The costal cartilages which unite with the
sternum are flattened laterally in the portions next the ribs, and
flattened from front to back in the rest of their extent.

In the horse the ribs increase in length from the first to the ninth;
they are flattened from without inwards, and increase in width from the
first to the sixth or seventh, and the following ones become narrower.
The costal cartilages, from the second to the eighth, are, as in the ox,
at first flattened laterally, near the ribs; while near the sternum they
are flattened from front to back.

In birds, the ribs are each furnished with a flat process (Fig. 18, 10),
which springs from the posterior border, is directed backwards, and
overlaps the external surface of the succeeding rib. These processes are
not found, as a rule, on the first or last ribs.

As for the costal cartilages, they are, as a rule, ossified, and receive
the name of inferior ribs (Fig. 18, 11), united to the preceding
(superior ribs; Fig. 18, 9) by articulation; by the other extremity they
are joined to the sternum; the first superior ribs generally want them.
Sometimes the last inferior rib becomes connected with the one that
precedes it, not articulating with the sternum; and thus recalls the
relations of the asternal ribs which we have noticed in our study of the
mammals.

In the bat, as in birds, the costal cartilages are ossified.


THE ANTERIOR LIMBS[5]

  [5] Consult Figs. 21, 33, 34, 38, 39, 46.

The anterior limbs, homologous to the upper limbs in man, are formed, as
in the latter, of four segments: the shoulder, the arm, the forearm, and
the hand. These limbs, considered in the vertebral series, present
themselves under very different aspects, which are determined by the
functions they are called upon to perform.

They constitute the forepaw in terrestrial mammals; in aerial
vertebrates they form wings; in aqueous mammals they act as paddles. In
whatever series we study them, we can readily find the relationship of
the different parts; it is very easy to recognise the same bones in the
upper limbs of the human being, the wings of the bat (Fig. 8) and of
birds (Fig. 21), and in the anterior paddles of the seal (Fig. 9) and of
the dolphin.

[Illustration: FIG. 8.--ANTERIOR LIMB OF THE BAT: LEFT SIDE, ANTERIOR
SURFACE.

1, Clavicle; 2, scapula; 3, humerus; 4, radius; 5, cubitus; 6, carpus;
7, thumb; 8, metacarpus; 9, phalanges.]

In quadrupeds, the shoulder and arm are hidden, the latter more or less
completely, in the muscular mass which binds it to the lateral wall of
the trunk; so that the anterior limbs only present; free from the trunk:
the elbow, forearm, and hand.


The Shoulder

In some vertebrates, the shoulder is formed of two bones--the scapula
and clavicle; in others of only one bone--the scapula; the clavicle in
this case does not exist.

=The Scapula or Omoplate.=--The scapula is situated on the lateral
surface of the thorax, and is directed obliquely, from above downwards
and from behind forwards.

We must first recall, so as to be able to make a comparison, that in man
this bone is placed at the posterior surface of the thoracic cage; so
that if we look at the human thorax on one of its lateral aspects we see
chiefly the external border of the scapula; it is the external surface
(homologous to the posterior surface of the human scapula) which we see
in its full extent when we look on the same surface of the thorax in
quadrupeds.

[Illustration: FIG. 9.--ANTERIOR LIMB OF THE SEAL: LEFT SIDE, EXTERNAL
SURFACE.

1, Scapula; 2, humerus; 3, radius; 4, ulna; 5, carpus; 6, metacarpus; 7,
phalanges of the fingers.]

To sum up, if we fancy the human being in the position of the quadruped,
the scapula will have its surfaces almost parallel to the ground (Fig.
10); while in quadrupeds, the surfaces are situated in a plane which is
almost perpendicular to the ground (Fig. 11). This position of the
scapula in an almost vertical plane is designed to give the necessary
point of support to the osseous columns that form the skeleton of the
other portions of the anterior limbs.

Because of this position of the scapula (Figs. 12 and 13), the spinal
border is superior, the cervical, anterior, and the axillary, posterior.
In direct contrast to what obtains in the human scapula, the spinal
border is the shortest of the three; except in the bat, and the
majority of the cetaceans.

[Illustration: FIG. 10.--SITUATION AND DIRECTION OF THE SCAPULA IN THE
HUMAN BEING, THE TRUNK BEING HORIZONTAL, AS IN QUADRUPEDS. VERTICAL AND
TRANSVERSE SECTION OF THE THORAX (DIAGRAMMATIC FIGURE).

1, Contour of the thorax; 2, 2, the scapula.]

[Illustration: FIG. 11.--POSITION AND DIRECTION OF THE SCAPULA IN
QUADRUPEDS. VERTICAL AND TRANSVERSE SECTION OF THE THORAX (DIAGRAMMATIC
FIGURE).

1, Contour of the thorax; 2, 2, the scapula.]

In certain animals (in the ungulates [_hoofed_[6]]--pigs, oxen, sheep,
horses) the superior, or spinal, border of the scapula is surmounted by
a cartilage called _the cartilage of prolongation_.

  [6] For the definition of the word _hoofed_, see p. 37.

This is the cause why the border to which it is fixed is so slightly
noticeable under the skin in these animals; indeed, in the upper part,
the bone and cartilage are not distinguishable in the contour of the
corresponding region of the back; being applied to the lateral surfaces
of the spinous processes, the prominence formed by the extremities of
which is directly continuous with the plane of the scapula (Fig. 16).

[Illustration: FIG. 12.--LEFT SCAPULA OF THE HUMAN BEING, POSTERIOR
SURFACE, PLACED IN THE POSITION WHICH IT WOULD OCCUPY IN THE SKELETON OF
A QUADRUPED.

1, Cervical border; 2, spinal border; 3, axillary border; 4,
supraspinous fossa; 5, subspinous fossa; 6, scapular spine; 7, glenoid
cavity; 8, coracoid process; 9, acromion process.]

[Illustration: FIG. 13.--LEFT SCAPULA OF A HORSE: EXTERNAL SURFACE.

1, Cervical border; 2, spinal border--the scapula here represented,
being from a hoofed animal, has a cartilage of extension attached to its
spinal border; 3, axillary border; 4, supraspinous fossa; 5, subspinous
fossa; 6, spine of the scapula; 7, glenoid cavity; 8, coracoid process.
The scapula of the horse has no acromion process, but it is easy, if we
compare the human scapula, to judge of the position which this process
would occupy if it were present.]

In quadrupeds whose scapula, on the contrary, is wanting in the
cartilage of prolongation (in the _clawed_,[7] such as the cat and dog),
the superior border of the scapula is visible, especially when the
animal is resting on its fore-limbs, particularly when it crouches; at
such a time the skin is markedly raised by that border; and the spinous
processes of the vertebræ, beyond which it projects, occupy the bottom
of a fossa (Fig. 15). The internal surface of the scapula is turned
towards the ribs; it is known, as in man (in whom this surface is
anterior), as the subscapular fossa.

  [7] For the definition of this word, see p. 37.

[Illustration: FIG. 14.--VERTICAL AND TRANSVERSE SECTION, AT THE SITE OF
THE SHOULDERS, OF THE THORAX OF THE HORSE (DIAGRAMMATIC FIGURE).

1, Outline of the thorax at the level of the third dorsal vertebra; 2,
2, scapula; 3, spinal border of the scapula; 4, cartilage of
prolongation; 5, contour of the skin.]

[Illustration: FIG. 15.--VERTICAL AND TRANSVERSE SECTION, AT THE PLANE
OF THE SHOULDERS, OF THE THORAX OF A DOG (DIAGRAMMATIC FIGURE).

1, Outline of the thorax at the level of the third dorsal vertebra; 2,
2, scapula; 3, spinal border of the scapula; 4, contour of the skin.]

Its external surface is divided into two parts by the spine of the
scapula; which, in some animals, terminates inferiorly in a flat and
clearly distinct process, the homologue of the acromion process of the
human scapula. The two regions separated by the spine are known as the
supraspinous fossa and the infraspinous fossa. The supraspinous fossa is
anterior to the spine, and the infraspinous is posterior to it. The
surfaces of the scapula are, in quadrupeds, flatter than in the human
being, and in particular the subscapular fossa, which is also less
concave. Some authors attribute this to the lesser curvature of the ribs
in quadrupeds. A few words will suffice to prove that there must be
another reason. The scapula is not in immediate contact with the ribs;
the subscapular fossa is not moulded on them. Besides, the form of the
scapula is, as in other parts of the skeleton, dependent on the
disposition of muscles, and the development of these latter is
correlated to the extent and energy of the movements which the
individual is able or required to execute. But the movements which
those muscles produce (more especially the rotation of the humerus) are,
in quadrupeds, less extensive than in the human being; and,
consequently, the muscles which produce them are, proportionally, less
strongly developed. The inferior angle (superior and external in man),
situated at the junction of the cervical and axillary borders, presents
the glenoid cavity, which, looking downwards, receives the articular
surface of the superior extremity of the bone of the arm--that is to
say, the head of the humerus. Above this cavity, on the lower part of
the cervical border, is situated a tubercle which reminds us of the
coracoid process of the human scapula. The region occupied by the
glenoid cavity is separated from the body of the bone by a
constriction--the neck of the scapula.

In birds the scapula is elongated in a direction parallel to the
vertebral column, and very narrow in the opposite (Fig. 18): it is also
flat, and has no spine. Its coracoid process is represented by a
peculiar bone--the coracoidean or coracoid bone--which we shall describe
later on when we come to the study of the clavicle and of the anterior
region of the shoulder (see p. 26).

=The Clavicle.=--The clavicle is found only in the human being, and in
animals whose anterior limbs, possessing great freedom of movement in
all directions, require that the scapula should possess a point of
support which, while affording this, can be displaced with it, or draw
it in certain directions. Now, this point of support is furnished by the
clavicle.

In animals possessed of hoofs (ungulates), such as the sheep, ox, and
horse, the clavicle does not exist. Indeed, in them the freedom of
movement of the anterior limbs is limited; they move by projection in
the forward and backward directions only; they merely fulfil the
functions of giving support to and carrying about the body. The clavicle
is rudimentary in the cat and the dog; in the cat it is a small,
elongated bone (Fig. 16), 2 centimetres in length, thin and curved,
connected with the sternum and the scapula by ligamentous bundles. In
the dog it is represented by a small osseous plate only (Fig. 17),
which is not connected with any of the neighbouring bones.

It is on the deep surface of a muscle which passes from the head and
neck to the humerus (mastoido-humeral, a muscle common to the arm, neck,
and head) in which this rudimentary bone is found to be developed.

The clavicle exists in perfect state in mammals which use their limbs
for digging, grasping, or flying; the insectivora (hedgehog, mole) and
some rodents (squirrel, woodchuck) are provided with it.

The cheiroptera (bats) possess an extremely well-developed clavicle, on
account of the varied movements which their thoracic limbs execute.

[Illustration: FIG. 16.--LEFT CLAVICLE OF THE CAT: SUPERIOR SURFACE
(NATURAL SIZE).

1, Internal extremity; 2, external extremity.]

[Illustration: FIG. 17.--CLAVICLE OF THE DOG (NATURAL SIZE).]

This formation of the shoulder which favours flight in the bat is even
more remarkable in birds. In these latter (Fig. 18) the clavicles, fused
together by their lower extremities, form one bone, having the shape of
the letter V or U, which is known as the _fourchette_; this bone, acting
as a true spring, keeps the shoulders apart, and prevents their
approximation during the energetic movements which flight necessitates.

In birds whose power of flight is strong, the two limbs of this bone are
widely separated and thick, and the fourchette is U-shaped. Those whose
flight is awkward and but slightly energetic have the limbs of the
fourchette slender; they unite at a more acute angle, and the bone is V
shaped.

Furthermore, a bone named the _coracoid_ joins the scapula to the
sternum; this bone, often fused with the scapula, where it contributes
to the formation of the glenoid cavity, represents in birds the coracoid
process of the human scapula. If we fancy this process directed
inwards, and sufficiently lengthened to join the sternum, we shall have
an idea of the disposition of the bone we are now discussing, and the
reasons for which the name has been chosen by which it is designated.
The coracoid bone, like the fourchette which it reinforces, offers to
the wings a degree of support proportionate to the efforts developed by
those limbs; for this reason it is thick and solid in birds of powerful
flight.

[Illustration: FIG. 18.--SKELETON OF THE SHOULDER OF A BIRD (VULTURE):
ANTERO-EXTERNAL VIEW OF THE LEFT SIDE.

1, Left clavicle; 2, inferior portion of the right clavicle, forming by
its ankylosis with that of the other side the fourchette; 3, coracoid
bone; 4, scapula; 5, articular surface for humerus; 6, superior half of
the sternum; 7, keel of sternum; 8, spinous process of the dorsal
vertebræ; 9, superior ribs; 10, process of one of these ribs; 11,
inferior ribs.]

The superior extremity of each branch of the fourchette, at the level of
its junction with the coracoid and the scapula, bounds, with these
latter, a foramen which gives passage to the tendon of the elevator
muscle of the wing, or small pectoral. The importance of the fourchette
being, as we have seen, in proportion to the movements of flying, it is
easy to understand that the bone is not found in the ostrich.


The Arm

A single bone, the humerus, forms the skeleton of this portion of the
thoracic limb.

=The Humerus.=--The bone of the arm is, in quadrupeds, inclined from
above downwards and from before backwards.

It is, with relation to other regions, short in proportion as the
metacarpus is elongated, and as the number of digits is lessened. In the
horse, for example, whose metacarpus is long, and in which but one digit
is apparent, the humerus is very short. The slight development in length
of the humerus explains its close application to the side of the animal
as far as the elbow.

In animals in which the humerus is longer, the bone is slightly free, as
well as the elbow, at its inferior extremity. Later on we will return to
the consideration of this peculiarity and of the proportions of the
humerus, after we have studied the other parts of the fore-limbs.

The humerus in quadrupeds is inflected like the letter S; in man this
general form is less accentuated, the humerus being almost straight. On
its body, which appears twisted on its own axis, we find the
musculo-spiral groove,[8] which crosses the external surface, and is
very deep in some animals. Above this groove, and on the external
surface, there exists a rough surface which is the impression of the
deltoid. In some species this rugosity is very prominent, and is called
_the tuberosity of the deltoid_; it is prolonged downwards by a border
which forms the anterior crest of the musculo-spiral groove and limits
this latter in front. The external border of the bone, or posterior
crest of the groove, limits it behind.

  [8] It would be going outside our province to discuss whether the
      humerus is really twisted on its axis. This question, often
      discussed, has been solved in some recent works in the following
      manner: the humerus has undergone torsion at the level of its
      superior extremity, and not at the level of its body; this does
      not authorize us further to accord any definite sense to the
      denomination 'groove of torsion' (musculo-spiral groove). That
      which we must especially remember in connection with this fact,
      is, as we shall afterwards see, the difference of direction which
      the articular head presents according as the torsion has been more
      or less considerable: because this is established, according to
      the same order, in man and in quadrupeds.

The superior extremity is enlarged, and remarkable in three portions
which it presents; these are: an articular surface and two tuberosities.

The articular surface, or head of the humerus, smooth and round, is in
contact with the glenoid cavity of the scapula. This head in the human
skeleton is directed upwards and inwards; in quadrupeds its direction is
upwards and backwards. The inferior extremity, having in both one and
the other its long axis directed transversely, and the point of the
elbow looking backwards in all, the result is that the head of the
humerus is not situated vertically above the same regions; in the first,
it is almost directly above the internal part of this extremity; in the
latter, it is situated above its posterior surface, or the point of the
elbow in the complete skeleton. This difference of direction is
correlated with the position of the scapula, the glenoid cavity of
which, as we have already seen, is in man turned outwards, whereas in
quadrupeds it looks downwards. In the latter case the scapula
consequently rests on the head of the humerus; and this position is most
favourable for the performance of the functions which the anterior limbs
have to fulfil in these latter.

Of the tuberosities of the head of the humerus, one is situated on the
external aspect--it is the great tuberosity, or _trochiter_; the other
is placed internally--it is the small tuberosity, or _trochin_. The
great tuberosity is divided into three parts--summit, convexity, and
crest; these different parts give insertion to the muscles of the
shoulder. We recollect that the facets (anterior, middle, and posterior)
of the great tuberosity of the humerus in man give attachment to the
muscles of the same region. The head of the humerus in the human body
projects above the tuberosities. We shall see afterwards, when dealing
with some special quadrupeds, that in some of these, on the other hand,
the tuberosities are on a higher level than the articular head of the
bone. Between the two tuberosities is the bicipital groove.

In man, the superior extremity of the humerus, although covered by the
deltoid, reveals its presence by elevating the corresponding portion of
the latter. In quadrupeds, the anterior part of this extremity, although
similarly covered by muscular bundles, produces a prominence under the
skin. This prominence is situated at the summit of the angle formed by
the opposing directions of the scapula and the bone of the arm, and
constitutes what is known by the name of the _point of the shoulder_, or
of the _point of the arm_.

The inferior extremity, transversely enlarged, presents an undulating
articular surface, which reminds us of the trochlea and the condyle of
the human humerus; on which, however, the condyle is more sharply
defined from the trochlea.

In the human skeleton, the internal lip of the trochlea descends lower
than the external; and also lower than the condyle. In the bear, the
cat, and the dog, it is the same. In the ox and the sheep, the condyle
is lower than the trochlea, but only very little lower. In the horse the
arrangement is still the same, but a little more accentuated.

On the lateral parts of this extremity we find: internally, a
prominence, the epitrochlea; and, externally, another, the epicondyle.
It is from this latter that the crest arises, which, passing upwards,
forms the posterior limit of the groove of torsion.

The two prominences, which we have just described from a general point
of view, present special arrangements which it is necessary to point
out. When we examine the form of the outline of the inferior extremity
of the humerus in man, the bear, the cat, the dog, the ox, and the
horse, we find in following this order that the extremity tends to
become narrow transversely, and that the epicondyle and the epitrochlea
are less and less prominent on the external and internal aspects
respectively. These two processes, indeed, project backwards; the
epitrochlea always remaining more developed than the epicondyle. Because
of this projection backwards, the cavity situated on the posterior
surface of the inferior extremity, the olecranon fossa, is very deep,
more so than in the humerus of man. Its borders being thus formed by the
two processes, are very prominent. In front we find the coronoid fossa,
which is less deep than that of which we have just spoken.

There exists in some mammals an osseous canal, situated above the
epitrochlea, and known as the _supratrochlear canal_ (Fig. 19). It is
bounded by a plate of bone which at its middle portion is detached from
the shaft of the humerus, and blends with the latter at both its
extremities. The brachial artery and median nerve pass through the
foramen.

[Illustration: FIG. 19.--INFERIOR EXTREMITY OF THE LEFT HUMERUS OF A
FELIDE (LION).

1, Epitrochlea; 2, supra-epitrochlear foramen.]

[Illustration: FIG. 20.--INFERIOR EXTREMITY OF THE LEFT HUMAN HUMERUS,
SHOWING THE PRESENCE OF A SUPRATROCHLEAR PROCESS.

1, Epitrochlea; 2, supra-epitrochlear process.]

A similar condition is sometimes found, as an abnormality, in
man, which presents itself under the following aspect (Fig.
20): an osseous prominence more or less long, in the shape of a
crochet-needle--supra-epitrochlear process--situated 5 or 6 centimetres
above the epitrochlea; the summit of this process gives attachment to a
fibrous band, which is inserted by its other end into the epitrochlea
and the internal intermuscular aponeurosis. The fibro-osseous ring thus
formed gives passage to the brachial artery and the median nerve, or in
case of a premature division of this artery to the ulnar branch of the
same.[9]

  [9] For further details of this anomaly, see Testut, 'The Epitrochlear
      Process in Man' (_International Journal of Anatomy and
      Physiology_, 1889); A. Nicolas, 'New Studies on the Supratrochlear
      Process in Man' (_Review of Biology of the North of France_, t.
      iii., 1890-1891).

There is also found in some mammals a perforation of the thin plate of
bone which, in others, separates the olecranon fossa from the coronoid.
This perforation is sometimes found as an abnormality in the human
humerus.

As does the sternum and the skeleton of the shoulder, the humerus of
birds presents differences correlated to the functions which the
thoracic limbs are destined to fulfil. Lying on the side of the thorax,
directed obliquely downwards and backwards (Fig. 21), it is
proportionately longer in individuals of powerful flight than in those
which fly less or not at all. In the vulture it projects beyond the
posterior part of the pelvis; in the cock it does not even reach the
anterior border of the same. To these differences in length are added
differences in volume and in the development of the processes which
serve for muscular attachment, which are more considerable in birds of
powerful flight.

The humerus is so placed that the radial border, external in man and
quadrupeds, looks upwards, with the result that the surface of the bone
of the arm, which in these latter is anterior, in the former looks
outwards. The humeral head, which is turned forwards and a little
inwards, is convex and elongated in the vertical direction. Behind and
above this head is found a crest for the insertion of muscles. It is the
same for the region below, where there is a tuberosity whose inferior
surface presents a pretty large opening which looks inwards to a fossa
from the floor of which a number of minute openings communicate with the
interior of the bone. This is the pneumatic foramen of the humerus.

It is of interest to remember in connection with this subject that in
birds, in keeping with the conditions of flight, every system of organs
is adapted to diminish the weight of the body. We particularly draw
attention to the osseous framework, the structure of which is such that
the weight of the animal is greatly lessened. This condition is secured
by the pneumaticity. The bone consists of a cover of compact tissue,
which, instead of enclosing marrow, is hollowed out by cavities which
contain air, and communicate with special pouches, the air-sacs, which
are appendages of the lungs.[10]

  [10] The presence of air in the bones does not seem to be always
       associated with the power of flight; as a matter of fact, we find
       air spaces in the bones of some birds which do not fly (E. J.
       Marey, 'The Flight of Birds,' Paris, 1890, p. 51).

[Illustration: FIG. 21.--SKELETON OF A BIRD (VULTURE): LEFT SURFACE.

1, Cranium; 2, face; 3, cervical vertebræ; 4, spinous processes of the
dorsal vertebræ; 5, coccygeal vertebræ; 6, sternum; 7, keel; 8, superior
ribs; 9, inferior ribs; 10, clavicle; 11, coracoid bone (for the details
of the skeleton of the shoulder, see Fig. 18); 12, humerus; 13, radius;
14, ulna; 15, carpus; 16, hand (for details of the skeleton of this
region, see Fig. 31); 17, ilium; 18, ischium; 19, pubis (for the details
of the pelvis, see Fig. 46); 20, femur; 21, tibia; 22, fibula; 23,
osseous nodule, which some anatomists think represents the calcaneum; it
is the sole vestige of the tarsus; 24, metatarsus; 25, foot; 26, first
toe (for the details of the skeleton of the foot, see Fig. 48).]

The antibrachial extremity of the humerus is flattened from without
inwards. It terminates in two articular surfaces, which articulate with
the radius and ulna.

The olecranon process of the ulna being slightly developed, it follows
that the olecranon fossa is not large; neither is the coronoid.


General View of the Form of the Forearm and Hand

We now proceed to the study of the two regions of the fore-limbs which
present the greatest variety in regard to the number of bones and also
in regard to form and proportions. These two regions are the forearm and
the hand.

It is first of all necessary to say that in man, when the fore-limb
hangs beside the body, and the dorsum of the hand looks backwards, the
two bones of the forearm are parallel, and that this position is known
by the name of _supination_. It is also necessary to remember that there
is another attitude, in which the radius, crossing the ulna, and
carrying the hand with it, displaces the latter in such a way that the
palmar surface looks backwards. This second position is known as
_pronation_.

Let us now suppose that a man wishes to walk in the attitude of a
quadruped. It will be necessary, in order that his upper limbs, being
for the moment anterior ones, may act as members of support, to place
the forearm in pronation, in order that, as is more normal, the hands
may rest on the ground by their palmar surfaces. In this position the
radius, being rotated on its own axis at its upper extremity and around
the ulna in the rest of its extent, shall have its inferior extremity
situated on the inner side of the corresponding extremity of the latter.

Such is the situation of the bones of the forearm and the attitude of
the hand in quadrupeds. In short, quadrupeds have their anterior members
in the position of pronation.

The individual whom we have just supposed placed in the attitude of a
quadruped would be able to maintain this position by pressing on the
ground more or less extensive portions of his hands; the whole palm of
the hand may be applied to the ground (Fig. 22); or the fingers
only--that is to say, the phalanges (Fig. 23); or the extremities of
the fingers only--that is to say, the third phalanges (Fig. 24). This
last position, which is certainly difficult to maintain, should here be
regarded rather as theoretical.

We shall meet with each of these modes of support in certain groups of
animals. Thus, the bear, badger, and the majority of rodents, have the
paws applied to the ground by the whole extent of the palmar surface of
the hand, from the wrist to the tips of the fingers. They are therefore
called plantigrade, from the analogy, in this case, of the palm of the
hand to the plantar surface, or sole of the foot.

[Illustration: FIG. 22.--THE HUMAN HAND RESTING FOR ITS WHOLE EXTENT ON
ITS PALMAR SURFACE: LEFT SIDE, EXTERNAL SURFACE.]

In others, such as the lion, tiger, panther, cat, wolf, and fox, the
support is made no longer on the whole extent of the palmar surface, but
on the corresponding surface of the fingers only--the metacarpus is
turned back, and, consequently, the wrist--that is to say, the
carpus--is removed from the ground. These are the digitigrades.

Lastly, the ruminants (sheep, oxen, deer, etc.), and also the pig, ass,
and horse, rest on the third phalanx only. In them not only is the
metacarpus turned back, but also the two first phalanges. The wrist is
very far removed from the ground. In these animals, the third phalanx is
enclosed in a case of horn, a nail (the hoof), and because the support
of the limb is on that nail, the name of unguligrades has been given
them. Nevertheless, as the point of support is on the third phalanx,
which is also known by the name of phalangette, we are of opinion that,
in order to specify definitely, although they walk on their fingers, as
do the digitigrades, the support is provided not by the whole extent of
those appendages, they might receive the name of phalangettigrades.

[Illustration: FIG. 23.--THE HUMAN HAND RESTING ON ITS PHALANGES: LEFT
SIDE, EXTERNAL SURFACE.]

[Illustration: FIG. 24.--THE HUMAN HAND RESTING ON THE TIPS OF SOME OF
ITS THIRD PHALANGES: LEFT SIDE, EXTERNAL VIEW.]

It is necessary among the ruminants to make an exception of the camel
and the llama, which are digitigrades.

Just in proportion as the hand is raised from the ground, as we have
just seen in passing from the plantigrades to the digitigrades and
unguligrades, the number of bones of that region diminishes, the bones
of the forearm coalesce, and the ulna tends to disappear; the hand
becomes less and less suitable for grasping, climbing, or digging, so as
to form an organ exclusively adapted for walking and supporting the
body.

Thus, the bear (plantigrade) has five digits, and the power of
performing the movements of supination and pronation. Indeed, we know
with what facility this animal is able to move his paws in every
direction, and climb a tree by grasping it with his fore-limbs. It is
well known, however, that no animal except the ape can perform the
movements of rotation of the radius around the ulna with the same
facility as man; and that none possesses the same degree of suppleness,
extent, and variety of movements of the forearm and hand.

In the digitigrades there is one finger which is but slightly developed,
and which is always removed from the ground--that is, the thumb: there
is also a little less mobility of the radius around the ulna.

In the ungulates the limbs are simply required to perform the movements
of walking, and form veritable columns of support, which become the more
solid as they are less divided. The bones of the forearm are fused
together; there is therefore no possibility of rotation of the radius
around the ulna. The metacarpus is reduced to a single piece, which in
the horse constitutes what is known as the _canon_. The number of digits
becomes diminished, so that in ruminants there are not more than two,
and in the horse but one. We should, however, add that, up to the
present, we have taken into account only perfect digits, those that rest
on the ground. We shall see further on that there exist supplementary
digits, but that they are only slightly developed, and are represented
in some cases by mere osseous spurs; it is this fact that has permitted
us to ignore them in the general study which we have just made.

Because, as we have already said, the unguligrades have the inferior
extremity of the digit encased in a horny sheath, which forms the hoof
of the horse and the corresponding structures (_onglons_) in the ox,
those animals have been placed in a special group, which is based on
that peculiarity--that is, the group of ungulate mammals.

The plantigrades and digitigrades, of which the paws have their surfaces
of support strengthened by an epidermic sole and fatty pads, have the
free extremities of the third phalanges covered on their dorsal surface
by nails or claws; hence they are named _unguiculate_ mammals.

The bat and birds have the bones of the forearm so arranged that the
radius cannot rotate around the ulna. This is necessary in order that
during flight, when the wing is being lowered, the radius and hand shall
not be able to turn; for, if such rotation took place, each stroke of
the wing would place it in a vertical position, which would occasion a
loss of resistance incompatible with the effect to be obtained.


The Forearm

The skeleton of the forearm in quadrupeds is vertical in direction;
consequently, it forms with the arm an angle open anteriorly; this is
well seen on examining the lateral surface. If we examine it on its
anterior surface, we find a slight obliquity directed downwards and
inwards. In animals in which the bones of the forearm are separate--that
is to say, susceptible of supination and pronation--we find a more close
resemblance to those of the human skeleton. The ulna, the superior
extremity of which always projects beyond that of the radius, has a
shaft which gradually narrows from above downwards. Its inferior
extremity is terminated by a round head in those animals in which the
ulna is fully developed; in others, as it is atrophied, it ends in a
thin, long process.

The ulna presents at its superior extremity a posterior process, the
olecranon, which forms the point of the elbow. We find on the anterior
surface of the same, another process, the coronoid.

It is necessary to dwell on the relations of these parts. In man the
head of the radius is situated at the anterior part of the external
surface of the superior extremity of the ulna (Fig. 25); indeed, the
small sigmoid cavity with which the head articulates is situated on the
outer side of the coronoid process, and this apophysis is placed in
front. In the plantigrades and digitigrades the head of the radius is
placed still more forward, so much so that it is situated almost in
front of the superior extremity of the ulna (Fig. 26). In the
unguligrades it is placed directly in front of this latter (Fig. 27).

Further, the displacement of the radius is made at the expense of the
superior extremity of the neighbouring bone; the radius appears to
appropriate more and more the parts which in man belong exclusively to
the ulna--for example, the coronoid process. In the plantigrades and the
digitigrades half of the process still belongs to the ulna and the
remainder to the radius. In the ungulates--the horse, for example--the
coronoid process belongs to the radius; the ulna, situated behind the
latter, is correspondingly diminished in size.

[Illustration: FIG. 25.--SUPERIOR EXTREMITY OF THE BONES OF THE HUMAN
FOREARM: LEFT SIDE, SUPERIOR SURFACE.

1, Radius; 2, ulna; 3, olecranon process; 4, coronoid process.]

[Illustration: FIG. 26.--SUPERIOR EXTREMITY OF THE BONES OF THE FOREARM
OF THE DOG: LEFT LIMB, SUPERIOR SURFACE.

1, Radius; 2, ulna; 3, olecranon process; 4, coronoid process.]

In brief, when we study this region of the skeleton in plantigrades,
then in digitigrades, and finally in unguligrades, we find a kind of
progressive absorption of one of the two bones (ulna) by the other
(radius), which thus becomes the more developed.

It is easy to explain this partial disappearance of the ulna. When the
forearm is capable of performing the movements of pronation and
supination, the ulna is completely developed, for it is in its small
sigmoid cavity that the head of the radius revolves, and it is around
its inferior extremity, the head, that the corresponding extremity of
the radius turns. But when the movements of rotation of the forearm do
not exist, the inferior extremity of the ulna becomes functionally
useless and disappears. As to its rôle in the movements of the region of
the wrist, that is nil, for we may remember--we will observe it again
when we come to treat of the articulations--that the hand articulates
with the radius alone (radio-carpal articulation); this is the reason
that, when the forearm possesses the fullest mobility, the hand follows
the movements which that bone makes around the ulna.

[Illustration: FIG. 27.--SUPERIOR EXTREMITY OF THE BONES OF THE FOREARM
OF THE HORSE: LEFT LIMB, SUPERIOR SURFACE.

1, Radius; 2, ulna; 3, olecranon process; 4, coronoid process.]

It is not so with the articulation at the elbow-joint; there it is the
ulna, which, with the humerus, forms the essential parts (humero-ulnar
articulation); its olecranon process limits the movement of extension
of the forearm. It is for this reason that, even in those quadrupeds in
which the ulna is atrophied, the olecranon process presents a relatively
considerable degree of development.

[Illustration: FIG. 28.--INFERIOR EXTREMITY OF THE BONES OF THE FOREARM
OF A MAN: LEFT SIDE, POSTERIOR SURFACE, POSITION OF SUPINATION.

1, Radius; 2, ulna; A, groove for the long abductor and short extensor
muscles of the thumb; B, groove for the radial muscles; C, groove for
the long extensor of the thumb; D, groove for the special extensor of
the index finger and of the common extensor of the fingers; E, groove
for the proper extensor of the little finger; F, groove for the
posterior ulna.]

[Illustration: FIG. 29.--INFERIOR EXTREMITY OF THE BONES OF THE FOREARM
OF THE DOG: LEFT SIDE, ANTERIOR SURFACE, NORMAL POSITION--THAT IS, THE
POSITION OF PRONATION.

1, Radius; 2, ulna; A, groove for the long abductor and for the short
extensor of the thumb; B, groove for the radials; D, groove for the long
extensor of the thumb, the special extensor of the index-finger, and the
common extensor of the fingers; E, groove for the special extensor of
the little finger.]

We know that on the posterior surface of the inferior extremity of the
bones of the human forearm are grooves in which pass the tendons of the
posterior and external muscles which, belonging to this region, are
directed for insertion towards the hand.

In animals, because of the movement of rotation of the radius, the
surface of this bone, which is anterior, corresponds to the posterior
surface of the same in man. (To possess a clear conception of this, it
is necessary to remember that, in this latter, the bones of the forearm
are always described as in the position of supination; they are thus
represented in Fig. 28. The direction of the surfaces of the radius is
the reverse of that in animals, since the latter have the radius always
in a state of pronation.)

Consequently it is on the anterior surface of the bone that we find the
grooves concerning which it is necessary to give some details. Regarding
them in passing from the radius towards the ulna, those grooves give
passage to the tendons of the muscles whose names occupy the columns on
p. 43. The letters which are referred to each serve to define their
order, and to facilitate reference to Figs. 28, 29, and 30.

[Illustration: FIG. 30.--INFERIOR EXTREMITY OF THE BONE OF THE FOREARM
OF THE HORSE: LEFT SIDE, ANTERIOR SURFACE.

1, Radius; A, groove for the long abductor and the short extensor of the
thumb; B, groove for the radials; D, groove for the common extensor of
the digits; E, groove for the special extensor of the little finger.]

We should mention that the groove E is situated, both in man and in the
dog, at the level of the inferior radio-ulnar articulation; but that in
the horse, as the ulna does not exist at that level, the groove is
situated on the external surface of the inferior extremity of the
radius. It is necessary to add that, in some horses, the ulna is,
nevertheless, represented in this region by a tongue-like process of
bone; and in such cases the groove is situated in front of this process,
at the level of the line of coalescence, which there represents the
articulation.

  -----------------------+-----------------------+-----------------------
           MAN.          |          DOG.         |         HORSE.
  -----------------------+-----------------------+-----------------------
  A. Long abductor of the|A. Long abductor of the|A. _Oblique extensor of
     of the thumb, and   |   thumb and short     |   the metacarpus_, the
     short extensor of   |   extensor of the     |   homologue of the
     the  thumb.         |   thumb united as one |   long abductor of the
                         |   muscle, _the oblique|   thumb and the short
                         |   extensor of the     |   extensor of the
                         |   metacarpus_.[11]    |   thumb, united as one
                         |                       |   muscle.
                         |                       |
  B. First and second    |B. The two radials     |B. The radials
     external radials    |   blended superiorly, |   represented by a
     (_extensor carpi    |   distinct inferiorly;|   single muscle, _the
     radialis longior_   |   this is _the        |   anterior extensor of
     and _brevior_).     |   anterior extensor of|   the metacarpus_.
                         |   the metacarpus_.    |
                         |                       |
  C. Long extensor of the|C. Long extensor of the|C. The long extensor of
     thumb.              |   thumb and special   |   the thumb and the
                         |   extensor of the     |   special extensor of
                         |   index finger united |   the index are
                         |   superiorly. These   |   absent.
                         |   muscles pass in the |
                         |   following groove.   |
                         |                       |
  D. Special extensor of |D. Common extensor of  |D. _Anterior extensor
     the index finger and|   the digits and the  |   of the phalanges_,
     the common extensor |   two preceding       |   the homologue of the
     of the fingers.     |   muscles.            |   common extensor of
                         |                       |   the digits.
                         |                       |
  E. Special extensor of |E. _Extensor of the    |E. Lateral extensor of
     the little finger.  |   third, fourth, and  |   the phalanges, the
                         |   fifth digits_, or   |   homologue of the
                         |   _the lateral        |   special extensor of
                         |   extensor of the     |   the little finger.
                         |   digits_, the        |
                         |   homologue of the    |
                         |   special extensor of |
                         |   the little finger.  |
                         |                       |
  F. The posterior ulnar |There does not exist on the forearm a groove
     (_extensor carpi    |for the posterior ulnar muscle, or _external
     ulnaris_).          |flexor of the metacarpus_.
  -----------------------+-----------------------------------------------

  [11] The words printed in italics are the names used in veterinary
       anatomy.

It is also useful to note, with reference to the groove F, in which
passes, in man, the tendon of the posterior ulnar muscle, that, when the
forearm is in pronation, the radius alone being displaced, we can only
see this groove on the surface which looks backwards; and that it is
then separated from the groove which contains the tendon of the special
extensor of the little finger by an interval equal to the thickness of
the head of the ulna.[12] When the forearm is supinated, the two grooves
are found, on the other hand, one beside the other: and the tendons
which they contain are very naturally in contact.

  [12] Édouard Cuyer, 'Shape of the Region of the Wrist in Supination
       and Pronation' (_Bulletin de la Société d'Anthropologie_, Paris,
       1888).

In birds the forearm is flexed on the arm, and the latter being directed
downwards and backwards, the former is, consequently, directed upwards
and forwards. Further, because of the position of the humerus, which, as
we mentioned on p. 32, has its inferior extremity so turned that the
surface which is anterior in man becomes external, the radius, instead
of being outside the ulna, is placed above it. This latter is larger
than the radius, but its olecranon process is very slightly developed.


The Hand

The hand in animals, as in man, is formed of three parts--the carpus,
metacarpus, and fingers. In man, the forearm and the hand being
described in the position of supination; the bones of the carpus are
named in passing from the most external to the most internal--that is to
say, from that which corresponds to the radial side of the forearm to
that which corresponds to the ulnar side. In animals in which, as we
know, but it is not unprofitable to repeat, the hand is in pronation,
the radial side of the forearm being placed inside, we enumerate the
carpal bones in counting the most internal as the first; this is the
only method which permits us, in taking our point of departure from the
human skeleton as our standard, to recognise the homologies of the bones
of the carpal region.

These bones, eight in number, are arranged in two transverse rows, of
which one, the first, is superior or antibrachial; the other, the
second, is inferior or metacarpal. Each of these rows contains four
bones. Considered in the order we have indicated above--that is to say,
proceeding from the radial to the ulnar side--they are thus named:
scaphoid, semilunar, cuneiform, and pisiform, in the first row;
trapezium, trapezoid, os magnum, and unciform, in the second. The number
of these bones is not the same in all animals on account of the
coalescence or absence of some. In each row the bones are placed side by
side, with the exception of the pisiform, which being placed on the
palmar surface of the cuneiform, produces a small projection in man, but
a very pronounced one in quadrupeds.

The pisiform is called the _hooked bone_ in some veterinary anatomies.
If we consider the hook which it forms, we may recognise that the name
is appropriate; but from the point of view of comparison with the human
carpus, the name is unfortunate, for it creates confusion between the
true pisiform (the fourth bone in the upper row), and the last bone in
the lower row, which is the veritable unciform bone. We do not here seek
for similarity of form, but homology of regions; and it is only by using
the same names to denote the same things that we can succeed in
determining such homology.

Taken as a whole, the bones of the carpus form a mass which, by its
superior border, articulates with the bones of the forearm, and by its
inferior border is in relation with the metacarpal region. Its dorsal
surface (anterior in quadrupeds) is slightly convex; its palmar surface
(posterior in quadrupeds) is excavated, and forms a groove in which pass
the tendons of the flexors of the fingers. This last, in man, has the
appearance of a gutter, because of the prominences caused by the
projection of the internal and external bones beyond their fellows.

In quadrupeds the palmar groove is especially determined by the pisiform
bone, of which we have just mentioned the great development.

The region occupied by the carpus, in the unguligrades, is known as the
_knee_; it would have been more appropriately named had it been called
the _wrist_.

The number of the metacarpal bones in mammals never exceeds five, but it
often falls below it; the same is true for the digits. The first are
generally equal in number to the latter; an exception is met with in
ruminants, whose two metacarpals coalescing soon after birth, form but
one bone; this, the _canon_ bone, articulates with two digits.

The number of metacarpals and digits diminishes in proportion as the
limbs cease to be organs of prehension, and become more exclusively
organs of support and locomotion.

The number of phalanges is two for the thumb and three for each of the
other digits; except in the cetaceans, in which they are more numerous.

In the bat, the metacarpals and phalanges are very long, and form the
skeleton of the wing; these phalanges are not furnished with nails; the
thumb, which is very short, is alone provided with one (Fig. 8).

With regard to the relative dimensions of the bones of the metacarpus,
it is necessary to remember that, in the human being, the second
metacarpal is the longest; then, in the order of decrease, come the
third, fourth, fifth, and first. In quadrupeds we shall also find
differences in length (see the chapter relating to the anterior limbs in
certain animals), but the order of decrease is not always that which we
have just mentioned.

In man the articular surface, situated at the inferior extremity of each
of the metacarpals, is rounded, and is called the head. This allows the
first phalanx, which is in relation with that surface, to be displaced
in every direction; indeed, this phalanx can not only be flexed and
extended, but it can also be moved laterally; this latter movement
allows of the fingers being separated and drawn together.

In quadrupeds which can only perform the movements of flexion and
extension of the digits--for example, the horse--the inferior extremity
of the metacarpal has not a rounded head of a regular outline; it is
marked by a prominent median crest, directed from before backwards, so
that the articular surfaces, which fit more exactly, form a sort of
hinge which allows of backward and forward movements only, and permits
no lateral displacement. In man, at the level of the inferior extremity
of the first metacarpal, in the vicinity of the articulation of this
bone with the first phalanx of the thumb, we find two sesamoid
bones--small bones developed in the fibrous tissue which surrounds the
articulation. We also meet with such structures, but more rarely, at the
level of the corresponding articulation of the index and auricular
digits; and, more rarely still, at those of the middle and ring fingers.
In quadrupeds, these bones are normally developed, and we shall see
afterwards that in some animals, as they reach a considerable size, they
are able to influence the external outlines; we shall see this, for
example, in the horse.

The hand, in birds, is directed obliquely downwards and backwards (Fig.
31). For the better understanding of its position in relation to the
forearm, we should remember that this latter, as we have described (p.
44), directed obliquely upwards and forwards, has the radius placed
above the ulna; the hand being oblique in the opposite direction and
placed under the forearm is, by this arrangement, inclined towards the
ulnar border of the latter.

[Illustration: FIG. 31.--SKELETON OF THE SUPERIOR LIMB OF A BIRD
(VULTURE): LEFT SIDE, EXTERNAL SURFACE.

1, Humerus; 2, radius; 3, ulna; 4, radial bone of the carpus; 5, ulnar
bone of the carpus; 6, first metacarpal; 7, second metacarpal; 8, third
metacarpal; 9, first digit, the homologue of the thumb; 10, first
phalanx of the second digit; 11, second phalanx of the second digit; 12,
third digit.]

For the rest, in order to be able to distinguish readily the
corresponding parts in the hand of a bird and that of a man, we merely
have to place the human forearm obliquely, in a direction upwards and
forwards (Fig. 32), the radius being above; this position we can obtain
by semi-pronation; then, to incline strongly the hand downwards and
backwards, moving the ulnar border of the hand towards the ulna; the
thumb is then anterior, the little finger posterior, and the palm of the
hand is turned towards the trunk.

The carpus in birds is formed by two bones only, with which the skeleton
of the forearm articulates. That which is in contact with the radius is
called the _radial bone of the carpus_; and that with which the ulna
articulates is named the _ulnar bone_.

[Illustration: FIG. 32.--SUPERIOR LIMB OF THE HUMAN BEING, THE DIFFERENT
SEGMENTS BEING PLACED IN THE ATTITUDE WHICH THE CORRESPONDING PARTS
OCCUPY IN BIRDS: LEFT SIDE, EXTERNAL SURFACE.]

The metacarpus is formed of three bones; the first, which is very short,
is fused at its superior extremity with the adjoining one; this latter
and the third, both longer than the first, but of unequal size, are
fused at their extremities. The metacarpal, which articulates with the
radial bone of the carpus, is larger than the one which is in line with
the ulna. To the metacarpus succeed three digits, of which the central
is the longest, and is formed of two phalanges; the other two are formed
each by a small, stylet-shaped bone. The middle finger, situated on the
prolongation of the metacarpal, which articulates with the radial bone
of the carpus, has its first phalanx large and flattened transversely;
this phalanx seems to have been formed by the union of two bones of
unequal development; the second phalanx is styloid in form. As to the
other two fingers, they are placed, one in front and the other behind;
the first, which articulates with the short metacarpal, fused at its
upper end with the principal bone of the metacarpus, in position
represents the thumb. The other, which is the third finger, articulates
with the inferior extremity of the thinnest bone of the metacarpus; it
is sometimes closely united to the corresponding border of the first
phalanx of the large--that is to say, of the median--digit.


The Anterior Limbs in Certain Animals

=Plantigrades=: =Bear= (Fig. 33).--The scapula of the bear approaches in
shape to a trapezium, of which the angles have been rounded off. The
anterior border (cervical) is strongly convex in the part next the
glenoid cavity. The junction of the superior (spinal) and the cervical
border forms almost a right angle, the summit of which corresponds to
the origin of the spine. At its posterior angle there is a prominence,
directed downwards, the surface of which is hollowed and is separated
from the infraspinous fossa by a crest, so that at this level a third
fossa is added to the infraspinous one. The neck of the scapula is but
slightly marked. The acromion is prominent, and projects a little beyond
the glenoid cavity.

The clavicle is rudimentary, but, as an example of the complete
development of this bone in plantigrade quadrupeds, we may cite the
marmoset.

The humerus is furnished at its superior extremity with a large
tuberosity, wide, and situated in front of the head of the bone; the
effect of this is that the bicipital groove is internal. As in man, the
great tuberosity does not reach so high as the humeral head, but it
approaches more nearly to that level. The deltoid impression is very
extensive, and descends pretty far down on the body of the bone. The
epitrochlea is prominent; the epicondyle is surmounted by a well-marked
crest, curved and flexuous in outline.

[Illustration: FIG. 33.--SKELETON OF THE BEAR: LEFT LATERAL SURFACE.

1. Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra; 6,
first dorsal vertebra; 7, fourteenth and last dorsal vertebra; 8, lumbar
vertebræ; 9, sacrum; 10, coccygeal vertebræ; 11, sternum; 12, ninth and
last sternal rib; 13, costal cartilages; 14, acromion process; 15, third
fossa on the external surface of the scapula; 16, great tuberosity of
the humerus; 17, musculo-spiral groove; 18, epicondyle; 19, radius; 20,
ulna; 21, olecranon process; 22, carpus; 23, pisiform; 24, metacarpus;
25, phalanges; 26, ilium, external fossa; 27, pubis; 28, tuberosity of
the ischium; 29, obturator foramen; 30, great trochanter of the femur;
31, condyles of the femur; 32, patella, or knee-cap; 33, anterior
tuberosity of the tibia; 34, fibula; 35, tarsus; 36, calcaneum, or
heel-bone; 37, metatarsus; 38, phalanges.]

The articular surface, which is in contact with the radius, is not a
regularly formed condyle; it is a little flattened on its anterior
surface, and presents at this level a slight depression which
corresponds to a small eminence on the anterior aspect of the superior
extremity of the radius. The surface which articulates with the ulna,
viewed on its anterior aspect, has the shape of a slightly-marked
trochlea; except at the level of the internal lip, which, as in man,
descends lower than the surface for articulation with the radius
(condyle). Behind, the trochlea is more clearly defined.

The bear possesses a considerable power of rotation of the radius; the
bones of the forearm are joined only at their extremities, while in the
remainder of their extent they are widely separated. The ulna terminates
below in a head and a styloid process; these articulate with the two
last bones of the first row of the carpus--viz., the cuneiform and
pisiform. The bones of the carpus are seven in number, the scaphoid and
the semilunar being fused together.

The metacarpals, five in number, differ very little from one another in
regard to length, though they increase in size from the first to the
fifth; this may be demonstrated by looking at the palmar surface of the
hand. It is the reverse of that which we find in man, for the fifth
metacarpal is the thickest of all, and the first is the most slender.

At the level of each metacarpo-phalangeal articulation are two sesamoid
bones.

The third digit is the longest. The terminal phalanges present two very
different portions: one, the anterior, is curved and pointed; it serves
to support the nail, whose shape it assumes; the other, posterior, forms
a sort of sheath into which the base of the nail is received.

The inferior portion of the posterior surface of this latter part
articulates with the second phalanx in the case of each of the last four
digits, but with the first phalanx in the case of the thumb.

[Illustration: FIG. 34.--SKELETON OF THE DOG: LEFT LATERAL SURFACE.

1, Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra; 6,
thirteenth and last dorsal vertebra; 7, lumbar vertebræ; 8, sacrum; 9,
coccygeal vertebræ; 10, anterior extremity of the sternum; 11, xiphoid
appendix; 12, ninth and last sternal rib; 13, costal cartilages; 14,
spinal border of the scapula; 15, supraspinous fossa of the scapula; 16,
infraspinous fossa of the scapula; 17, great tuberosity of the humerus;
18, deltoid impression; 19, musculo-spiral groove; 20, olecranon
process; 21, radius; 22, carpus; 23, pisiform; 24, metacarpus; 25,
sesamoid bones; 26, phalanges; 27, ilium, iliac crest; 28, pubis; 29,
tuberosity of the ischium; 30, great trochanter of the femur; 31,
patella, or knee-cap; 32, anterior tuberosity of the tibia; 33, fibula;
34, tarsus; 35, calcaneum, or heel-bone; 36, metatarsus; 37, sesamoid
bones; 38, phalanges.]

[Illustration: FIG. 35.--SCAPULA OF THE DOG: LEFT SIDE, EXTERNAL
SURFACE.

1, Posterior or axillary border; 2, superior or spinal border; 3,
anterior or cervical border; 4, spine of scapula; 5, coracoid process;
AA´, length of spinal border.]

[Illustration: FIG. 36.--LEFT SCAPULA OF THE CAT: EXTERNAL SURFACE.

1, Posterior or axillary border; 2, superior or spinal border; 3,
anterior or cervical border; 4, spine of the scapula; 5, coracoid
process; AA´, length of the spinal border.]

=Digitigrades=: =Cat=, =Dog= (Fig. 34).--In these animals the anterior
(cervical) border of the scapula is convex; the posterior (axillary)
border is straight or slightly concave. The supraspinous and
infraspinous fossæ are of equal extent (Figs. 35 and 36). The neck is
short. The spine of the scapula becomes more and more prominent towards
its inferior extremity, where it ends in a twisted and inflexed portion,
which represents the acromion process; this process terminates at the
level of the glenoid cavity. The coracoid process is represented by a
small tubercle, slightly curved inwards; this tubercle is situated
above the glenoid cavity, at the inferior part of the cervical border.

In the dog, the posterior angle, formed by the junction of the axillary
and the superior (spinal) borders, is obtuse; the spine rises
perpendicularly from the surface of the bone. The width of the scapula,
measured at the level of the spinal border (from A to A´, Fig. 35),
equals about half the length of the spine. We must, however, make an
exception for the turnspit dog, in which the superior border equals
three-fourths of that length. The scapula is, in this case, of a more
compact type; it is broader, but shorter. In the cat, the anterior
outline of the scapula, formed by the union of the cervical border and
the corresponding half of the spinal, is more convex; the posterior
angle is not obtuse, as in the dog. The spine is bent slightly downwards
and backwards; before terminating in the acromion process it presents a
triangular projection, the apex of which is directed downwards. The
tubercle which represents the coracoid process is curved inwards more
strongly than that of the dog, thus resembling more closely the
appearance of this process in the human being.

All proportions considered, the scapula of the cat is broader than that
of the dog; its width, measured along the length of its spinal border
(from A to A´, Fig. 36), equals three-fourths of the length of the
spine.

The clavicle is rudimentary; it is, however, better developed in the cat
than in the dog. The clavicle of the cat is represented by a small,
elongated bone, curved in outline, the convexity being turned forward;
it is united to the acromion and the sternum by ligamentous fibres; that
of the dog is merely a scale-like osseous plate situated on the
posterior surface of a muscle of this region (see Figs. 16 and 17).

The humerus is long and twisted in the shape of an S. The inferior
articular surface has the form of a simple pulley, for the condyle is
very slightly marked. The internal part of this articular surface
descends lower than the external; this condition resembles that found in
the human being, where the inner lip of the trochlea is lower than the
condyle.

In the dog, the olecranon fossa communicates with the coronoid by an
opening.

In the cat, there is a supra-epitrochlear canal (see Fig. 19), but no
olecranon perforation.

The bones of the forearm articulate at their extremities. The body of
the radius is united to the body of the ulna by a short, thick,
interosseous ligament; the fibres of this ligament, though short, do not
prevent the production of some movements at the articulations of the
bones.

The radius so crosses the ulna that above, it is in front and external
to the latter, while below, it is internal. This bone is flattened from
front to back, and slightly convex anteriorly. Its superior extremity is
formed, externally, of a portion which represents the head of the radius
in man; internally, by another portion which represents half of the
coronoid process of the ulna, which, in the human being, belongs
exclusively to the latter (see p. 39, the encroachment of the radius on
the ulna). This extremity is surrounded with a vertical articular
surface which is placed in contact with a small cavity which is hollowed
out on the ulna (the lesser sigmoid cavity); and presents at its
superior aspect a surface which articulates with the inferior extremity
of the humerus. The shaft of the bone has on its internal border
rugosities analogous to the imprint of the pronator radii teres of the
human skeleton; these rugosities, indeed, give insertion to a muscle of
the same function, and bearing the same name. The inferior extremity,
broader than the superior, is hollowed on its external aspect by a small
cavity which receives the inferior extremity of the ulna; its inferior
surface (concave) articulates with the carpus; its anterior surface (the
homologue of the posterior surface of the corresponding extremity of the
human radius) presents grooves which serve for the passage of the
tendons of the muscles which pass from the forearm to the back of the
hand. (For the names of the muscles whose tendons pass in these grooves,
see Fig. 29.)

The ulna is furnished at its superior extremity with an olecranon
process, which is more prominent than that of the human ulna; this
process is compressed laterally, and its internal surface is hollowed;
there we also find a great sigmoid cavity, and a coronoid process
situated at the internal part of the anterior surface, a process which,
as we have previously shown, it shares with the radius.

The shaft of the bone, prismatic and triangular, diminishes in thickness
as it approaches the lower extremity, which articulates with the
corresponding extremity of the radius. In the dog, the ulna terminates
inferiorly in a blunt point, without enlargement, analogous to the head
of the human ulna; in the cat, by a head which is prolonged into a
styloid process, by which it articulates with a portion of the carpus.

The carpus consists of seven bones--three in the superior row and four
in the inferior. In the superior row the scaphoid and semilunar bones
are fused together. The pisiform is elongated and expanded at its two
extremities; it forms a prominence which, directed backwards, projects
beyond the level of the other bones of this region.

The metacarpal bones are five in number; they are enumerated from within
outwards; they articulate with the carpus and with each other. The
inferior extremity of each metacarpal bone presents the form of a
condyle in front; and is divided behind so as to form two lateral
condyles, which are separated by a median crest; on these posterior
condyles are applied two small sesamoid bones. The metacarpal bone of
the thumb is very short; the third and fourth are the longest. The
metacarpus, as a whole, is directed vertically.

The phalanges are three in number for each finger, except the thumb,
which has but two. The first phalanx, directed almost horizontally
forwards, is the longest; the second is directed downwards and forwards;
the third consists of two portions: a posterior part, which forms a sort
of sheath into which the base of the nail is received; and an anterior,
conical in form, and curved in crochet shape, which forms a support for
the nail (Fig. 37).

The third and fourth digits are the longest; the second and fifth are of
equal length; the thumb is the shortest; it does not touch the ground,
and does not even reach the articulation of the metacarpal bone and
first phalanx of the second finger.

In the cat, the metacarpal bone of the thumb, although shorter than any
of the others, is quite as thick. The third digit is a little longer
than either the second or fourth. In animals of this genus, the claws,
in the condition of repose, are retracted, and removed from the ground;
this prevents their being worn, and thus preserves their sharpness. At
such times the third phalanx is received into a groove which is found on
the external surface of the second phalanx. In the dog, the claws are
not tractile.

[Illustration: FIG. 37.--SKELETON OF THE FINGER OF A FELIDE (LION): LEFT
SIDE, INTERNAL SURFACE.

1, Metacarpus; 2, sesamoid bones; 3, first phalanx; 4, second phalanx;
5, third phalanx; 6, gutter for the reception of the base of the nail;
7, prominent osseous crest formed to lodge in the concavity of the
nail.]

[Illustration: FIG. 38.--SKELETON OF THE PIG: LEFT LATERAL SURFACE.

1, Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra; 6,
first dorsal vertebra; 7, fourteenth and last dorsal vertebra; 8, lumbar
vertebræ; 9, sacrum; 10, coccygeal vertebræ; 11, anterior extremity of
the sternum; 12, xiphoid appendix; 13, seventh and last sternal rib; 14,
costal cartilage; 15, cartilage of prolongation of the scapula; 16,
great tuberosity of the humerus; 17, olecranon process; 18, radius; 19,
ulna; 20, pisiform; 21, metacarpus; 22, phalanges of the two great toes;
23, phalanges of the external toe; 24, ilium; 25, pubis; 26, tuberosity
of the ischium; 27, great trochanter; 28, knee-cap; 29, anterior
tuberosity of the tibia; 30, fibula; 31, tarsus; 32, calcaneum; 33,
metatarsus; 34, phalanges of the two great toes; 35, phalanges of the
external toe.]

=Unguligrades=: =Pig= (Fig. 38).--The scapula is markedly narrowed in
the region above the glenoid cavity. The spine is atrophied at both its
extremities, so that at its inferior part we do not find the acromion
process. In its middle portion the spine is prominent, and presents a
triangular process which turns backwards, overlapping a part of the
infraspinous fossa; this latter is much larger than the supraspinous.
The spinal border is surmounted by the cartilage of prolongation, the
superior margin of which is convex; this cartilage extends posteriorly
beyond the posterior (axillary) border of the bone.

The small tuberosity of the superior extremity of the humerus is but
slightly developed; the great tuberosity, on the contrary, is very
large. The bicipital groove is situated internal to this. The deltoid
impression is scarcely marked.

The forearm is short, directed obliquely downwards and inwards, thus
forming with the hand an angle, of which the apex is directed inwards.
The two bones of the forearm are strongly bound to one another by an
interosseous ligament, which is formed of very short fibres. The radius
appropriates, at its superior extremity, the coronoid process of the
ulna. The latter is, notwithstanding, well developed in the rest of its
extent; it has a flattened shaft which almost completely overlaps the
posterior surface of the radius; its inferior extremity reaches to the
carpus.

The carpus is formed of eight bones--four in the superior row, and four
in the inferior. The third bone of the superior row (cuneiform) is more
in contact with the ulna than with the radius.

There are but four metacarpal bones; there is no metacarpal of the
thumb. The two median metacarpal bones are the longest; they are those
which correspond to the digits which alone touch the ground. The
internal digit and the external one are thin and short; they are
functionless, as a rule, taking no part in supporting the limbs on the
ground. Notwithstanding this, they are formed, as the other digits, of a
number of phalanges, which give them the semblance of perfect digits.
(We shall soon see that in certain animals there exist digits which,
being incomplete with regard to the numbers of their constituent bones,
more accurately merit the name of imperfect digits.)

The third phalanges are each enclosed in a horny hoof, to which the name
of _onglon_ has been given.

We have already drawn attention to the smaller lateral digits, and
noted the general fact that they do not come in contact with the ground.
It is necessary to modify this statement by adding that under certain
conditions they give a slight amount of support; for example, when the
individual is the subject of excessive obesity, the limbs yield under
the weight, and the nails of the lateral digits may touch the ground.

A similar fact may be noticed in pigs of ordinary bulk at the moment
when, during walking, each of the fore-limbs commences to bear the
weight--that is to say, when it is directed obliquely downwards and
forwards; then all the digits are in contact with the ground.

=Unguligrades (Ungulates)=: =Sheep=, =Ox= (Fig. 39).--The scapula, which
is of elongated form, is very narrow in the vicinity of the glenoid
cavity. The spine, which becomes more and more salient towards its
inferior part, terminates abruptly in a border, which, forming an acute
angle with the crest, produces a projection which represents the
acromion process--a very rudimentary acromion, for it does not reach the
level of the glenoid cavity. The supraspinous fossa is much smaller than
the infraspinous; it hardly equals one-third the extent of the latter.
The anterior border, thin and convex in its superior portion, is concave
in the rest of its extent; the posterior border is thick and slightly
concave; the spinal border is surmounted by the cartilage of
prolongation. In the ox the spine of the scapula, in its middle portion,
is flexed a little backwards on the infraspinous fossa.

[Illustration: FIG. 39.--SKELETON OF THE OX: LEFT LATERAL SURFACE.

1, Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra; 6,
first dorsal vertebra; 7, thirteenth and last dorsal vertebra; 8, lumbar
vertebræ; 9, sacrum; 10, coccygeal vertebræ; 11, sternum; 12, xiphoid
appendix; 13, eighth and last sternal rib; 14, costal cartilages; 15,
spine of scapula; 16, cartilage of prolongation of the scapula; 17,
great tuberosity of the humerus; 18, musculo-spiral groove; 19,
olecranon process; 20, radius; 21, carpus; 22, pisiform; 23, metacarpus;
24, rudimentary metacarpal; 25, sesamoid bones; 26, first phalanges; 27,
second phalanges; 28, third phalanges; 29, anterior iliac spine; 30,
pubis; 31, tuberosity of the ischium; 32, great trochanter; 33,
supracondyloid fossa of the femur; 34, patella, or knee-cap; 35,
anterior tuberosity of the tibia; 36, fibula; 37, coronoid tarsal bone;
38, tarsus; 39, calcaneum; 40, metatarsus; 41, rudimentary metatarsus;
42, sesamoid bones; 43, first phalanges; 44, second phalanges; 45, third
phalanges.]

The great tuberosity of the humerus is highly developed; its summit,
very prominent, is flexed over the bicipital groove; a prominence of the
small tuberosity also bends over the groove, with the result that at
this level the latter is converted into a sort of canal. At the inferior
extremity the condyle, although not large, is recognisable; for it is
separated from the trochlea by a depression in form of a groove. In
contrast to the condition found in man, the condyle descends to a level
a little below that of the internal lip of the trochlea. (For the
arrangement of the epicondyle and the epitrochlea, see p. 30.) In the
sheep, the deltoid impression is but slightly marked; in the ox, it is
more evident.

The forearm is directed obliquely downwards and inwards, so as to form,
with the hand, an angle of which the apex is internal; this angular
outline of the _knee_ (wrist) is so characteristic of ruminants that the
corresponding region of the horse, when salient inwards, receives the
name of _ox-knee_. The radius bears the coronoid process, and the larger
part of the articular surface which comes in contact with the inferior
extremity of the humerus; the condyle and the trochlea articulate with
the radius in front; while behind, the trochlea articulates with that
part of the sigmoid cavity which belongs to the ulna. The posterior
surface of the shaft of the radius is flattened; its anterior surface is
slightly convex. The inferior extremity articulates with the carpus by a
surface which is directed obliquely downwards and inwards. The shaft of
the ulna is very slender, and fused in its middle third with the body of
the radius; it terminates below, at the level of the external part of
the inferior extremity of the radius, by a slightly expanded portion
which, fused with this latter, forms the articular surface for the
carpal bones.

In the ox the forearm is short; in the sheep it is proportionally
longer.

The bones of the carpus are six in number--four in the upper row, and
two in the lower; they form an irregular cuboid mass which contributes
to the formation of the region known as _the knee_ in ruminants, as in
the horse; we have already remarked that the name 'wrist' would be more
accurate. The anterior surface in its foremost part is vertical, and is
slightly convex from side to side. At its posterior and external part
the pisiform bone forms a prominence.

The metacarpus consists of two bones only--one, well developed, which is
known as the principal metacarpal, or the _canon_ bone (this is the name
given to the region in the hoofed animals); and a rudimentary one, which
is situated at the superior and external aspect of the preceding
metacarpal. Sometimes there is found a third metacarpal at the internal
aspect; but, when present, it is but very slightly developed.

The principal metacarpal consists of two metacarpals fused together; on
this account the bone is longitudinally marked in the median line by a
slight depression which marks the junction of the two bones of which it
is formed. In some ruminants (certain species of chevrotains) the
coalescence does not take place, and the two metacarpals remain
separate.

The anterior surface of the principal metacarpal is convex transversely;
its posterior surface is flattened. The superior extremity of this bone
articulates by two facets with the two bones of the inferior row of the
carpus; on the internal part of the anterior surface of this extremity
is found a tubercle. The inferior extremity is divided into two parts by
a fissure or notch; each part is articular, and consists of two separate
condyles, which are separated from each other by an antero-posterior
crest; on each side of this crest, and behind, are found two sesamoid
bones. As for the external rudimentary metacarpal bone, it is nothing
more than a small, short tongue of bone; which, in goats and sheep, is
often absent.

The division of the inferior extremity of the principal metacarpal into
two parts is correlated with the two perfect digits which give the foot
of the ruminant its forked appearance. Each digit consists of three
phalanges, which are directed obliquely downwards and forwards; further,
these phalanges are inclined a little outwards from the axis of the
limb, so that the two digits diverge from each other as they descend.

The first phalanx, which is the longest, articulates superiorly with the
principal metacarpal; its inferior extremity terminates in a trochlea,
and the lip of this, which is situated towards the axis of the limb,
descends lower than that of the opposite side; this arrangement is
correlated with the divergent direction of the digits. The second
phalanx has its superior extremity moulded on the trochlea which
terminates the extremity of the first; its inferior extremity is
articular, and elongated from before backwards. On the posterior
surface of this extremity is found a sesamoid bone.

With regard to the third phalanx, it presents the form of a triangular
pyramid, and displays a postero-superior concave surface with which the
second phalanx articulates; an anterior, convex surface, which
terminates in a point on its anterior part; and an internal surface,
which is flattened. The third phalanx of each digit is contained in a
hoof (_onglon_).

There is also found in ruminants two imperfect rudimentary digits, which
are represented by two small bones situated behind the articulation of
the metacarpal and the digits which we have just been studying. These
rudimentary digits are each enveloped in a layer of horn; they
constitute the _spurs_. The two digits of the ruminants represent the
third and fourth fingers of the human hand; the two lateral digits,
greatly atrophied, are the homologues of the second and fifth fingers;
the thumb is not present.

It is the same as regards the metacarpal bones, which form, by their
union, the principal metacarpal; the external represents the fourth
metacarpal, and the internal the third. It is to the latter that the
tubercle, of which we have already made mention, belongs; and with the
signification of which, because it gives attachment to a muscle, we
shall concern ourselves in the section on myology (see Radial Muscles).

=Unguligrades=: =Horse= (Fig. 40).--The scapula is narrow, compared with
that of the animals we have just been considering. The anterior border
is convex in its superior portion, and concave in its inferior; the
posterior border is slightly hollowed out. The supraspinous fossa is
less in extent than the infraspinous; but the difference is less
than that between the same fossæ in the ox and the sheep; in the
ox, as we have already indicated, the proportion is one-third; in
the horse, one-half. The spine, which disappears at the extremities,
is rough and thick in its middle third, there forming a kind of
tuberosity--_tuberosity of the spine_. Above and in front of the glenoid
cavity is found a strong process consisting of a rugous base, and a
summit which is directed inwards. This forms a kind of hook curved
towards the inside; it represents the coracoid process. The scapula is
surmounted by the cartilage of prolongation, of which the superior
border, which is thin and curved, is parallel to the superior border of
the prominence of the withers; the cartilage forms, consequently, the
lateral surface of this region. The cartilage of prolongation undergoes
ossification in old horses. The humerus is short; the bicipital groove,
situated on the anterior surface of the superior extremity, separates
the greater tuberosity from the lesser, and is divided into two parts by
a median ridge; it is this portion of the humerus which forms the
prominence known as the _point of the shoulder_, or _point of the arm_.
The deltoid impression well deserves the name of tuberosity which has
been given to it, for it is very prominent; the musculo-spiral groove is
very deep.

[Illustration: FIG. 40.--SKELETON OF THE HORSE: LEFT LATERAL SURFACE.

1, Cranium; 2, face; 3, atlas; 4, axis; 5, seventh cervical vertebra; 6,
first dorsal vertebra; 7, eighteenth and last dorsal vertebra; 8, lumbar
vertebræ; 9, sacrum; 10, coccygeal vertebræ; 11, sternum; 12, xiphoid
appendix; 13, eighteenth and last sternal rib; 14, costal cartilage; 15,
scapula; 16, cartilage of extension; 17, great tuberosity of the
humerus; 18, deltoid crest; 19, olecranon process; 20, radius; 21,
carpus; 22, pisiform; 23, principal metacarpal; 24, metacarpal,
external rudimentary; 25, large sesamoids; 26, first phalanx; 27,
second phalanx; 28, third phalanx; 29, ilium, showing external iliac
fossa; 30, pubis; 31, tuberosity of the ischium; 32, great trochanter;
33, infratrochanteric crest, or third trochanter; 34, supracondyloid
fossa of the femur; 35, knee-cap; 36, anterior tuberosity of the tibia;
37, the fibula; 38, tarsus astragalus; 39, calcaneum; 40, principal
metatarsal; 41, rudimentary external metatarsal; 42, large sesamoids;
43, first phalanx; 44, second phalanx; 45, third phalanx.

_To face p. 64._]

At the inferior extremity, the trochlea is large; the portion
corresponding to the condyle of the humerus in man is, in proportion to
the latter, of small extent. The olecranon fossa is deep. The epicondyle
and the epitrochlea are somewhat different from those of the human bone.
In the latter, the epitrochlea is salient towards the inner side,
causing an increased transverse diameter of the inferior extremity of
the humerus. In the horse--it is the same in ruminants--this tuberosity
projects backwards, folds on itself in forming the internal boundary of
the olecranon cavity, and exceeds in diameter, in the antero-posterior
direction, the prominence of the epicondyle, which presents a nearly
similar arrangement. This latter has, however, a part which, projecting
externally, is situated at the inferior part of a crest, that forms the
posterior boundary of the musculo-spiral groove. The result is that,
contrary to the condition found in the human being, the epicondyle is
more prominent transversely than the epitrochlea, but this latter is
more salient on the posterior aspect. The epitrochlea and the epicondyle
offer a larger surface for the origin of muscles of the forearm than the
same prominences in the human bone do for the analogous muscles of the
same region.

Some veterinary anatomists have given to the inferior and external
articular surface of the humerus the name of trochlea; and to the
internal one, that of condyle. On this account they designate the
external prominence as the epitrochlea, and the internal one as the
epicondyle. In addition to the fact that this point of view is not
legitimate, it produces inevitable confusion when comparing the parts
with those of the human humerus, and this confusion exists, not alone in
describing the bone, but also in the description of the muscular
attachments, and in the comparison of the muscles of the forearm of
quadrupeds with the corresponding muscles in the human species.

The radius is placed in front of the ulna; its body, slightly convex
forwards, has the anterior surface convex transversely, and the
posterior surface plane in the same direction. It is to the external
part of this latter that the ulna is applied, which is completely fused
with the radius.

The superior extremity of the radius is a little larger than the
inferior. Its superior aspect, concavo-convex, moulded on the inferior
articular surface of the humerus, presents internally two cavities,
which receive the lips of the trochlea, and, externally, another,
smaller, cavity, which receives the condyle. The radius articulates with
the trochlea and the condyle, having appropriated a portion of the ulna,
as is proved by the presence of the coronoid process, which belongs to
the former. This superior extremity presents, internally, a tuberosity
into which the biceps is inserted; this is the bicipital tuberosity; and
on the other side is another tuberosity, which is a little more
prominent than the preceding.

The inferior extremity, which is flattened from before backwards, is
furrowed on its anterior surface by grooves for the passage of muscles
(the names of the muscles whose tendons pass in these grooves have
already been given on p. 43). It articulates at the lower end with the
superior row of the carpus, and it terminates laterally in tuberosities:
one, external, on which is found a groove for the tendon of the lateral
extensor of the phalanges, the homologue of the special extensor of the
little finger; the other, internal, is a little more prominent than the
one we have just described. These tuberosities are visible under the
skin which covers the superior and lateral parts of the region known as
the _knee_; but which, we again repeat, is no other than the wrist.

The ulna has a triangular shaft, situated at the posterior surface of
the radius, with which it is fused. It disappears completely at the
level of the inferior third of the forearm. Occasionally, in some
horses, the ulna is abnormally long, in the form of a slender tongue of
bone; and extends to the neighbourhood of the external tuberosity of the
inferior extremity of the radius (see Fig. 79, p. 196). Its superior
extremity is chiefly represented by the olecranon process, which is
voluminous in bulk, and forms the projection known as the point of the
elbow. This process is flattened laterally; its internal surface is
excavated; the anterior surface, which is concave, forms a part of the
great sigmoid cavity; the remainder of the cavity is formed by the
radius.

In the ass, the ulna is a little longer than in the horse--that is to
say, it descends lower; and the radius is a little more convex
anteriorly.

The carpal bones are seven in number--four in the superior row, and
three in the inferior. The trapezium is wanting in the latter.
Sometimes, however, in certain varieties of horses the trapezium is
developed, but then it is no more than a very small osseous nodule. The
pisiform bone, situated at the external part of the first row of bone,
is prominent posteriorly. It is of rounder form and flattened from
without inwards. It articulates with the trapezium and the radius. It
presents, on its external surface, a groove for the passage of the
tendon of the posterior ulnar muscle, which is named by veterinary
anatomists the _external flexor of the metacarpus_.

The carpus, as a whole, is of an irregularly cuboid shape; its anterior
surface, slightly convex from side to side, forms the skeleton of the
region of the _knee_ (wrist). The metacarpus is formed of three bones:
the principal metacarpal and the two rudimentary ones.

The principal metacarpal, which forms the region of the _canon_, is
directed vertically; its anterior surface is slightly convex
transversely. This surface is covered by a number of tendons, which
slightly alter its appearance; so that it is the principal base of this
part of the fore-limb. Its posterior surface is flattened. The superior
extremity of this metacarpal presents plane surfaces, variously
inclined, with which the bones of the inferior row of the carpus
articulate. On the anterior surface, and a little to the inner side, is
found a tuberosity, which is destined for the insertion of _the anterior
extensor of the metacarpus_, the homologue of the radial muscles. The
inferior extremity is formed by two condyles, an internal and an
external; between which is found a median crest.

This extremity, the superior extremity of the first phalanx, which
articulates with it, together with two sesamoid bones--the great
sesamoids--which are situated on its posterior surface, collectively
form the region which from its rounded outlines is called the _ball_.

With regard to the rudimentary metacarpals, external and internal, to
which some authors give the name of _fibulæ_, they are applied to the
sides of the posterior surface of the principal metacarpal. They are
elongated bones, of which the superior extremity, which is a little
thickened, is called the _head_; the lateral bones of the second row of
the carpus partly rest on the heads of these. They become more slender
as they descend, and terminate opposite the inferior fourth of the
principal metacarpal. Each ends in a slight swelling, to which the name
_button_ has been given. The internal one is the better developed.

The rudimentary metacarpals are vestiges of atrophied digits, as will be
explained further on.

The single finger of the horse consists of three phalanges. The first
phalanx, which is directed obliquely downwards and forwards, corresponds
to the constricted region situated below the 'ball,' and known as the
_pastern_. It is flattened from before backwards; its anterior surface
is convex transversely, while the posterior surface is plane. Its
superior extremity is moulded on the inferior extremity of the principal
metacarpal, and its inferior extremity, which is smaller, presents a
trochlea with which the second phalanx articulates. This is also
directed downwards and forwards, and is shorter. It corresponds to the
region which, situated between the pastern and the hoof, is known as the
_cornet_.

The third phalanx, situated entirely within the hoof, has the same
direction as the first and second. It is large and broad, and presents
three surfaces separated by well-marked angular borders (see Fig. 96).
The anterior surface is oblique downwards and forwards; it is convex
transversely. The inferior surface is slightly hollowed, and is in
relation with the sole, or plantar surface of the hoof.

The superior surface, which is articular, is divided by a median ridge
into two lateral cavities, which correspond to the trochlea on the
inferior surface of the lower extremity of the second phalanx. The
inferior border corresponds in shape with the hoof. The superior border
presents in its median part a projection, _the pyramidal eminence_,
which prolongs at this level the anterior surface of the bone. Finally,
the posterior border, which is concave, is in contact with a sesamoid
bone, _the lesser sesamoid_, which increases the superior articular
surface behind, and is also in contact with the second phalanx.

As we have just seen, the horse possesses but one digit. In the
ancestors of the animal--that is, in the prehistoric species which
are now extinct (_orohippus_, _miohippus_, _protohippus_, or
_hipparion_)--the number of digits was larger; this fact conclusively
proves that the rudimentary metacarpals of the existing horse are
vestiges of digits which have disappeared through want of use. In the
first of those ancestors--orohippus--there were four digits; all save
the first, the thumb, being then developed. In the others of the series
there existed but three digits. It must, however, be noted that in those
animals it is always the digit which corresponds to the middle finger of
the pentedactyl hand that is longest. In other less ancient species the
lateral fingers are reduced to the condition of mere splints of bone. It
follows from what has been said that the digit which persists in the
equine species should be considered as the third finger, and that the
rudimentary metacarpals represent lateral digits considerably
atrophied.

This disappearance of the lateral digits cannot excite surprise when we
consider the functions of the organs. Becoming useless, they must
undergo gradual atrophy from want of use.

There undoubtedly is, in this former existence of supplementary digits
in the horse, something analogous to what we still find in the pig;
where the two principal digits are accompanied by two shorter ones,
which very probably, from their infrequent use, are destined to
disappear in a more or less distant future.


Proportions of the Arm, the Forearm, and the Metacarpus

As a supplement to the study of the anterior limbs which we have just
finished, it appears necessary to give some indications of the relative
proportions of certain of the segments which form these limbs in the
plantigrades, the digitigrades, and the ungulates.

First, we would remark that, in following this order of classification,
the scapula becomes less and less narrow, and assumes a form more and
more elongated. In order to convince ourselves of this, it will be
sufficient to study the bone first in man, then in the bear, the cat,
dog, ox, and finally in the horse.

As to the proportions of length, which are those we should chiefly
study, we shall commence with the comparison of the forearm and
arm--that is to say, the radius and the humerus. The radius is found to
be longer in proportion to the humerus, as the number of digits is
smaller, and the hand loses more and more the functions of an organ of
prehension. In man, the radius is shorter than the humerus; in the
horse, on the contrary, it is longer.

To give an idea of this proportion, we shall employ what is known as the
antibrachial index. This index gives the relation which exists between
the length of the forearm and that of the humerus; the length of this
latter, whatever may be the actual measurement, is represented by a
fixed figure, the number 100. A very simple arithmetical operation
gives the proportion--

  forearm × 100
  -------------, the quotient obtained furnishes the index.
     humerus

The index is less than 100 if the forearm is shorter than the bone of
the arm. The index is more than 100 if, on the contrary, the forearm is
longer.

In man, the radius is shorter than the humerus; indeed, in adult
individuals of the white race the average index is 74.

In the bear, the length of the radius approaches closely to that of the
humerus; the index is about 90. In the skeleton of a bear in the
anatomical museum of the École des Beaux-Arts, the humerus is 33
centimetres in length, and the radius 30 centimetres.

In the cat, the radius is very little shorter than the humerus. In the
dog they are equal. The antibrachial index of the latter is,
accordingly, 100.

In the horse, the radius is longer than the humerus; the index is
therefore above 100. Thus, in the skeleton of the horse which we have in
the museum of the École des Beaux-Arts, the index is 113--length of
humerus, 29 centimetres; length of radius, 33 centimetres. In other
skeletons which we have measured we found: in one, 108--humerus, 34
centimetres; radius, 37 centimetres; in another, 116--humerus, 25
centimetres; radius, 29 centimetres.

The metacarpal bone undergoes, relatively to the humerus, a proportional
elongation, analogous to that of the forearm.

In man, the length of the metacarpus is contained about 5-1/2 times in
that of the humerus; in the bear, it is contained 4 times; in the dog,
2-1/2 times; in the horse, 1-1/3 times only.

It is well known that the proportions vary according to race, and that
what we have here given are but the general indications.


The Articulations of the Anterior Limbs

The knowledge of human arthrology which we presume the reader to have
previously acquired makes it unnecessary for us to enter into numerous
details regarding the configuration of the articular osseous surfaces
and the disposition of the fibrous bands that retain them in position.
Accordingly, in the description which follows, and also in that of the
articulations of the posterior limbs, we shall occupy ourselves but very
briefly with the details above referred to, so as to devote ourselves
especially to the indication of the movements--that is to say, of that
which, while easily comprehended on recollection of former studies,
presents the greatest interest from the artistic standpoint in these
studies in comparative anatomy.

=The Scapulo-Humeral Articulation.=--The head of the humerus and the
glenoid cavity of the scapula being in contact, the two bones are bound
together by a rather loose articular capsule, which is strengthened by
the muscles of this region which fulfil the function of active
ligaments.

This articulation, so movable in every direction in the human species,
is not so much so in quadrupeds; the arm in the latter, as also the
shoulder, being kept in contact with the lateral region of the thorax by
the numerous muscles which surround it.

Of the movements performed by the humerus, flexion and extension are the
most extensive; those of abduction and adduction are much less so.

It is necessary, before proceeding further, to determine what the two
principal movements which we have just mentioned really are, viz.,
flexion and extension.

We know that in man the displacements of the humerus which take place in
the antero-posterior direction are known as movement or projection
forwards, and movement or projection backwards, respectively. We do not
say that the humerus is flexed or extended, because, in reality, on
account of the position which the skeleton of the shoulder occupies, it
is not able to flex or place itself on the line of prolongation of the
scapula with which it articulates.

In quadrupeds it is not so. The humerus and the scapula are contained in
almost the same vertical plane; and the bone of the arm can take, in
relation to the latter, the positions characteristic of flexion and
extension--that is, of approach to the scapula and removal from it.

What makes the meanings of these terms a little confusing is that, in
human anatomy, some authors consider the backward movement of the
humerus as extension, and the forward movement as flexion; in order to
be able to compare these movements to those that the femur executes in
relation to the pelvis.

Now, in our opinion, the indication of this correspondence is not
absolutely necessary; since it ceases to be exact if we wished, from the
point of view of the direction given to other segments of the skeleton,
to establish the same relation between the elbow and the articulation of
the knee.

It is therefore indispensable, when discussing quadrupeds, to
discontinue these terms, in order the more readily to recognise that: in
flexion the inferior extremity of the humerus is directed backwards; in
extension, on the contrary, it is directed forwards. In the first case
the humerus approaches the scapula; in the second, on the contrary, it
moves away from it.

These movements, which take place during walking, are executed in the
following manner: When one of the anterior limbs is at the end of that
stage of progression which is called support (see p. 289, Displacements
of the Limbs)--that is to say, during the time that the foot remains in
contact with the ground, whilst the trunk is moving forward--the
direction of this limb becomes more and more oblique downwards and
backwards. At a certain moment the limb is raised from the ground, to be
carried forwards, in order to be again pressed on the ground, and
recommence a new resting stage. In these different phases the humerus is
flexed. But at the moment that the limb, when carried forwards, is about
to resume its contact with the ground it becomes directed obliquely
downwards and forwards; then the humerus is in the position of
extension.

During these movements of the humerus, there exists an essential
factor--that is, the scapular balance. (It is the same as what occurs in
man when he balances his arm in the antero-posterior plane.) When the
humerus is flexed, the scapula moves in such a way that the superior
portion projects forwards; when it is extended, the scapula, on the
other hand, is inclined more backwards. But it is necessary to add that,
during these displacements, the scapulo-humeral angle varies; it tends
to close during the flexion of the humerus, and becomes more open during
extension.

The movements and the relations of the humerus and the scapula are
clearly represented in Figs. 41 and 42, reproduced from the
chromophotographic studies of Professor Marey--studies relative to the
analyses of the movements of the horse.[13] They show clearly the
movements of flexion and extension of the humerus, also the balancing of
the scapula which accompanies the movements.

  [13] E. J. Marey, 'Analyses of the Movements of the Horse by the
       Chromophotograph' (_La Nature_, June 11, 1898).

[Illustration: FIG. 41.--FLEXION OF THE HUMERUS: RIGHT ANTERIOR LIMB OF
THE HORSE, EXTERNAL SURFACE (AFTER A CHROMOPHOTOGRAPHIC STUDY BY
PROFESSOR MAREY).]

[Illustration: FIG. 42.--EXTENSION OF THE HUMERUS: RIGHT ANTERIOR LIMB
OF THE HORSE, EXTERNAL SURFACE (AFTER A CHROMOPHOTOGRAPHIC STUDY BY
PROFESSOR MAREY).]

=The Articulation of the Elbow, or the Humero-ulnar Articulation.=--In
this articulation, which is constructed in the form of a true hinge, the
movements of flexion and extension alone are possible. In flexion, the
forearm, directed forwards, is folded on the arm, with which, in certain
circumstances, it comes in contact. For example, in a horse of mettle
which leaps over an elevated obstacle, the animal forcibly raises his
fore-limbs by flexing them. Flexion is produced to the same extent, and
even more so, and for a longer period, in felides which crouch.

In extension, on the contrary, the forearm is carried backward. This
movement being limited only by the contact of the tip of the olecranon
with the bottom of the olecranon fossa of the humerus, the forearm is
enabled, in this case, to move until it is in line with the arm. For
example, during walking, when one of the anterior limbs, having reached
the end of its resting stage, is considerably inclined downwards and
backwards.

The apex of the olecranon process--that is to say, the point of the
elbow--forms a marked prominence, more salient in flexion than in
extension, as in the corresponding region of the human elbow.

=The Radio-ulnar Articulation.=--It is in the dog and the cat, in which
the two bones of the forearm articulate by their extremities only, and
remain separate in the rest of their extent, that the articulations call
for special notice.

In the upper part, the radius rotates on itself; while below, it rotates
around the ulna. It follows that the forearm, which in all quadrupeds is
in a state of permanent pronation, can, in carnivora, take the position
of supination, or rather, of demi-supination. In fact, whatever be the
mobility of the two bones of the forearm, the movement is not able to
bring the palmar surface to the front, but only to direct it towards the
median line.

=The Articulation of the Wrist.=--Here are found, as in man, three
superimposed articulations: the radio-carpal, intercarpal, and
carpo-metacarpal.

If we remember the movements which take place at the plane of these
articulations in man, and take account of the fact that the mobility of
the limbs is reduced just in proportion as they are simplified in
structure so as to become organs of support only, we can easily
comprehend that, in the horse and the ox, and, in a word, animals that
have a canon bone, the movements of the wrist are little varied in
character, while in carnivoræ, on the other hand, they are relatively
more so.

We will remember that in the ox and the horse the region of the wrist is
called the _knee_.

In flexion, the hand is bent backwards; in extension it is carried
forwards. These two movements take place especially in the radiocarpal
and intercarpal articulations. In the first of these articulations, it
is the superior row of the carpus which glides backwards and forwards on
the corresponding articular surface of the forearm. In the second
articulation, it is the second row which moves; gliding on the inferior
articular surfaces of the row above it. This inferior row carries the
metacarpus with it; for the carpo-metacarpal articulation is much less
mobile than either of the other two.

In flexion, the articular surfaces are separated from one another in
front; and the changes of form which result from this are noticeable on
the anterior surface of the 'knee.' Moreover, at that moment this region
contrasts markedly in its outlines with the parts above it and below
it--that is to say, with the corresponding surfaces of the forearm and
of the canon bone.

As for the lateral movements, by which the hand is inclined outwards and
inwards in its movements at the wrist, they exist to an appreciable
extent in the cat and the dog only; in order to understand this, it is
enough to compare the shape of the articular surfaces of this region in
carnivora and the horse, for example. In the latter, those surfaces are
almost plane; in the cat, on the contrary, they are curved (inferior
surface of the forearm, concave; superior border of the carpus, convex).
These latter, then, are, in form, similar to those which exist at the
same level in the human being; this explains the possibility of
analogous movements of the whole hand--that is to say, of the movements
of abduction and adduction.

=The Metacarpo-phalangeal Articulations.=--With regard to the mobility,
it is in these articulations, as in those of the wrist--that is to say,
although in all quadrupeds the first phalanges can be flexed and
extended on the metacarpus, it is only in the cat and dog that lateral
movement is possible. Indeed, in the horse, in which the principal
metacarpal terminates inferiorly in two convex surfaces, which are
separated by a crest; and where the whole articulates with a cavity on
the superior extremity of the first phalanx; because of the hinging of
these surfaces, there can only be movements of opening and closing of
this articulation. The first phalanx is directed backwards during
flexion and forwards during extension. In the dog and the cat the digits
can be separated from each other, and also drawn together--that is to
say, abducted and adducted; but, as in man, these movements can be made
only when the first phalanges are in the state of extension. During
flexion they are impossible, because of the tension of the lateral
ligaments, which increases as the flexion is more pronounced. This can
be demonstrated, for example, in the cat, which, in order to separate
the digits, opens the hand widely--that is to say, forcibly raises the
first phalanges.

=The Interphalangeal Articulations.=--The phalanges are in contact with
one another by surfaces, which, on one side, are of trochlear form, and,
on the other, are moulded on these trochleæ; accordingly, at the level
of these articulations, the movements of flexion and extension only can
take place.

In the felidæ, the claws which the third phalanges bear cannot be
utilized when the latter are in a state of extension, at which time,
being forcibly raised, they are, in fact, placed on the outer sides of
the phalanges, which are grooved to receive them. But when the animal
wishes to use them, it flexes those third phalanges, of which the
terminal extremity is then projected forward, and the claws are ready to
fulfil their function. But at the same time it extends the first
phalanges, to produce a certain tension of the flexors of the digits,
and thus enable the latter to act with greater efficacy, with a minimum
of contraction. We can demonstrate this action experimentally on
ourselves. It is enough to carry the first phalanges forcibly into a
state of extension; the third phalanges then become flexed, quite
spontaneously, by the tension of the tendons of the flexors which are
inserted into them.

At the same time, if we examine the felidæ which we have taken as
examples, when the first phalanges are in the state of extension, the
digits will be found to be separable, as we have already indicated in
connection with the metacarpo-phalangeal articulations, with the result
that the claws are then able to lacerate a wider surface.

The extension of the ungual phalanx, which determines the retraction of
the claw and stops its action, is the mechanical result of an elastic,
fibrous apparatus which is attached to each of the third phalanges, and
has its origin of the second.


THE POSTERIOR LIMBS[14]

  [14] Examine Figs. 21, 33, 34, 38, 39, 49.

The posterior limbs are divided, as are the inferior limbs of the human
being, of which they are the homologues, into four parts: pelvis, thigh,
leg, and foot.


The Pelvis

The pelvis, which incompletely limits the abdominal cavity, inferiorly
in the vertical position of the body and posteriorly in the normal
attitude of quadrupeds, is formed by the iliac bones and sacrum--the
coccyx forming a prolongation of the latter. We have already described
the two latter (pp. 10 and 11) in connection with the vertebral column,
of which they form the inferior or posterior portion or segment,
according to the attitude of the individual.

=The Iliac Bone.=--The iliac or coxal bone, is a paired or
non-symmetrical bone, united below to its fellow of the opposite side,
while it is separated from it above by the sacrum.

In all animals, as well as in man, the iliac bone, at the beginning of
life, consists of three parts, which afterwards unite and fuse together
and join at the middle of the bottom of a deep cavity which is situated
on the outer aspect of the bone--the cotyloid cavity.

Of those three portions when examined in the human iliac bone, that
above the cavity is the ilium; that on the inside is the pubis; and the
last, the lower one, is the ischium. In quadrupeds, the iliac bone
being, in its entirety, directed much more obliquely downwards and
backwards, the relative position of these constituent parts is a little
modified: the ilium is in front, the pubis is still internal, but in a
more inferior position, and the ischium is behind the cotyloid cavity.
We notice this peculiarity of the development of the iliac bone because
it is customary to continue to apply to the osseous regions which
correspond to these parts the names by which they were known when
independent bones.

[Illustration: FIG. 43.--THE LEFT ILIAC BONE OF THE HUMAN BEING:
EXTERNAL SURFACE, PLACED IN THE POSITION WHICH IT WOULD OCCUPY IN THE
SKELETON OF A QUADRUPED.

1, Cotyloid cavity; 2, ilium; 3, iliac crest; 4, anterior iliac crest;
5, posterior iliac spine; 6, pubis; 7, tuberosity of the ischium; 8,
obturator foramen; 9, ischiadic spine.]

[Illustration: FIG. 44.--LEFT ILIAC BONE OF A QUADRUPED (HORSE):
EXTERNAL SURFACE.

1, Cotyloid cavity; 2, ilium, external iliac fossa (directed upward in
the horse); 3, iliac crest; 4, anterior iliac spine (directed inwards in
the horse, it is the angle of the haunch); 5, posterior iliac spine
(directed inwards in the horse; it is the angle of the haunch); 6,
pubis; 7, tuberosity of the ischium; 8, obturator foramen; 9, ischiadic
spine, or subcotyloid foramen.]

The bones which form the skeleton of the pelvis of quadrupeds are
proportionally more elongated and less massive than those of the human
pelvis (Figs. 43 and 44).

We find, on the external surface of the iliac bone, the cotyloid cavity,
whose border is interrupted by the cotyloid notch; a deep notch which
looks downwards.

In front of this cavity is the ilium. This portion, narrow in the part
which is next the cavity, is directed forwards and upwards, expanding
more and more as it passes upwards. It presents an external or superior
surface (external in some animals, superior in others), which recalls
the external iliac fossa; and an internal or inferior surface, at the
superior part of which is found the auricular surface for articulation
with the sacrum.

The anterior border of the ilium is rough; this is the iliac crest, at
the extremities of which we find, below or outside, a prominence which
corresponds to the anterior superior iliac spine of man; and internally
another projection which corresponds to the posterior iliac spine.

Immediately above the cotyloid cavity is a rough crest, which is known
as the _supracotyloid crest_, which is, however, no other than the
homologue of the sciatic spine. In front of this prominence, the border
of the ilium, which is notched, forms the great sciatic notch.

If, still taking the cotyloid cavity as the point of departure, we
proceed inwards--that is, towards the median line of the body--we find
the pubis; if in a posterior direction, the ischium. These two portions,
pubis and ischium, limit an oval orifice, the subpubic foramen.

In the human skeleton, the pubis of one side is united to that of the
opposite side, to form the pubic symphysis. In the animals which we are
now studying a portion of the ischium enters into the formation of the
symphysis; in other words, it is formed, not only by the body of the
pubis, but also by the descending branch or ramus of the pubis and a
portion of the ascending branch or ramus of the ischium, which are fused
with those of the opposite side. It results that, though in the human
being the symphysis is short and the ischio-pubic arch large, in
quadrupeds it is the opposite. In them the arch is a mere slot, and
being formed by the ischium alone, merits the name of the ischial arch.
The ischio-pubic symphysis is very large, and forms a horizontal surface
relatively extensive, a sort of floor, on which rest certain organs
which occupy the cavity of the pelvis.

The posterior and external angle of the ischium is rough and prominent;
it is the tuberosity of the ischium. This forms a projection under the
skin; it also does in man when the trunk is strongly inclined forwards,
while the thighs are maintained in the vertical position. In
marsupials--opossum, kangaroo, and phalanger--the pelvis at its pubic
region is surmounted by two bones, situated one on each side of the
median line, and arranged in the form of a fork of two prongs (Fig. 45).
These, which are called _marsupial bones_, support the pouch which, in
animals of this genus, lodges their young, which, at the time of birth,
are incapable of supporting a separate existence, their development
being absolutely incomplete.

[Illustration: FIG. 45.--PUBIC REGION OF THE PELVIS OF A MARSUPIAL
(PHALANGER, FOX).

1, Symphysis pubis; 2, obturator foramen; 3, marsupial bones.]

In the cetaceans--for example, the dolphin--because of the absence of
posterior limbs, the pelvis is represented by two separate bones only,
which have no connection with the vertebral column. In birds, the pelvis
is remarkable for its elongated form (see for its form Fig. 21, and for
details Fig. 46). The cotyloid cavity is pierced by an opening, and
presents on its posterior border, which is here a little prominent, a
surface with which the great trochanter is in contact.

The ilium is very highly developed, and is fused in the median line with
the ilium of the opposite side, the last dorsal vertebræ, the lumbar
vertebræ, and the sacrum. Because of these relations with the dorsal
vertebræ, it is in contact anteriorly with the last ribs, which
consequently emerge from each side of the iliac region of the pelvis.

The ischium forms a plate of bone which, in part, closes the external
portion of the cavity of the pelvis. Its superior border is separate for
a certain distance from the external border of the ilium; there is thus
left an opening of more or less considerable size, which represents or
takes the place of the great sciatic notch.

[Illustration: FIG. 46.--PELVIS OF A BIRD (THE COCK): EXTERNAL SURFACE,
LEFT SIDE.

1, Ilium; 2, ischium; 3, pubis; 4, inferior extremity of the pubis; 5,
sciatic foramen; 6, oval foramen, homologous to the obturator; 7,
coccygeal vertebræ.]

The pubis, long and slender, is in connection with the inferior border
of the ischium, of which it follows the general direction; and
circumscribes with this latter, below the cotyloid cavity, an oval
orifice, which is the homologue of the obturator foramen. Its inferior
extremity reaches beyond the corresponding part of the ischium, bending
towards the middle line, but without joining the pubis of the opposite
side. On this account there is no symphysis pubis in birds.
Nevertheless, an exception must be noted in the case of the ostrich, the
pubic bones of which meet in the middle line, and are articulated in
form of a symphysis.


The Thigh

A single bone, the femur, forms the skeleton of this portion of the
lower limb.

=The Femur.=--The bone of the thigh is, in man, directed downwards and
inwards; this obliquity, we may remind the reader, is due to the
difference in length of the two condyles which form its inferior
extremity; the internal is the more prominent, the result of which is
that when the femur is held vertically, the internal condyle descends
lower than the external. Now, as those two articular expansions rest on
the horizontal plane formed by the upper extremity of the tibia, it
follows that the superior part of the femur inclines towards the side of
the shorter condyle--that is to say, outwards--and that, the leg being
vertical, it and the bone of the thigh unite in forming an angle, of
which the apex is directed towards the inner side of the knee.

In many mammals the two condyles are equally prominent, the result of
which is that the femur inclines neither inwards nor outwards, but is
contained in a plane parallel to the axis of the trunk; while the leg is
included in the same plane. Nevertheless, although contained in the
plane which we have just indicated, the femur is obliquely placed, and
directed downwards and forwards; it accordingly forms, with the pelvis,
an angle, of which the opening is directed to the anterior aspect of the
body.

In reptiles and in birds the femur and leg are both placed in the same
plane, but this plane is not parallel to the axis of the trunk. This is
the result, on the one hand, of the thorax being wide, and, on the other
hand, of the femur, which is directed forwards, being in contact by its
anterior extremity with the lateral aspect of the costal region, it is
thus necessarily placed in a direction forwards and outwards, and the
knee is further removed from the axis of the trunk than is the
articulation which unites the thigh with the pelvis.

The femur, like the humerus, is almost completely enveloped by muscular
masses, which bind it to the lateral walls of the abdomen. Its inferior
extremity alone is free, and is always the more so in proportion to its
elongation--that is to say, as it belongs to an animal whose foot is
more divided. The femur in this respect conforms to the law which we
have indicated in connection with the bone of the arm, in which the
development, as to length, is in proportion to the division of the hand.

If we compare the femur of certain animals with that of man, we see that
the corresponding details of form are readily recognisable, but they are
slightly modified. Thus, on examining the superior extremity, we find
there a head, a neck, a great trochanter, and a lesser; but the neck is
usually short and thick, and the great trochanter does not occupy the
same level with regard to the articular head of the bone. In man, the
great trochanter does not rise to the level of the head of the femur; in
the dog and the cat it approaches that level; in the horse and in
ruminants it rises above it.

With regard to the inferior extremity, its surfaces undergo
modifications which are further accentuated as we pass from the
digitigrades to the ungulates, or unguligrades. We know that in man the
femoral trochlea is continuous behind, without interruption, with the
condyles--that is to say, that each of the condyles is the continuation
of one of the lips of the trochlea. We have just said that the trochlea
is continuous without interruption with the condyles; this is accurate.
Nevertheless, we must remark that, at the level of the junction of these
surfaces, the bone presents a slight constriction, which is more marked
on the external than on the internal aspect. This constriction, which is
but slightly marked in man, is accentuated in the dog and the cat; in
the ruminants and the solipeds it is still more pronounced so that we
may say that in these latter the trochlea and the condyles are almost
completely separated.

There is another modification in regard to the prominence and extent of
the two lips of the trochlea. In man, the external lip of the trochlea
reaches higher than the internal, and it is more prominent in front. In
the dog, these lips are equal with regard to thickness, but the external
still reaches higher than the internal; in the cat, they are equal in
every respect; in ruminants and solipeds the internal lip is wider,
thicker, and rises higher than the external.

In animals the trochlea is, as a general rule, narrower than in man, and
the condyles are more prominent posteriorly; so that, when viewed from
one of the lateral aspects, the inferior extremity of the femur is, in
them, better developed in the antero-posterior direction.

In birds, the femur is shorter than the bones of the leg; its great
trochanter is in contact with a prominence which occupies the posterior
part of the border of the cotyloid cavity. Instead of articulating at
the level of the knee, with the knee-cap and tibia only, as in man, it
articulates, in addition, with the superior extremity of the fibula. A
similar arrangement is found in marsupials and reptiles.

=The Knee-cap.=--This bone, developed in the thickness of the tendon of
the triceps muscle of the thigh, is in contact, by its posterior
surface, with the femoral trochlea. The two articular surfaces which are
applied to the lips of the trochlea present, with regard to their
extent, an inequality which is in proportion to the arrangement which we
have above indicated--that is, while in man it is the external surface
which is the larger, in the horse it is the internal. We shall see what
the general form of the knee-cap is when we come, later on, to study
more particularly the posterior limbs of some animals.


The Leg

The skeleton of the leg consists of two bones: the tibia and the fibula.
The tibia is the more internal and the larger of the two; the fibula is
slender, and situated on the outer side, and a little posterior to, the
preceding. The fibula is more or less developed according to the
species; in some it is complete, in others it is very much atrophied.

This peculiarity may be compared with that which we have drawn attention
to regarding the development of the ulna; but here the seriation is less
distinct. Not only in the different species, but even in the individuals
of the same species, the development of the fibula presents little
regularity. In quadrupeds, the bones of the leg are directed obliquely
downwards and backwards, so that they form, with the femur, which is
directed obliquely downwards and forwards, an angle, the apex of which
is placed at the anterior surface of the knee.

=Tibia.=--The tibia of quadrupeds is readily comparable with that of
man; as in the case of the latter, its shaft has three surfaces--an
external, which is hollowed out in its upper portion, and becomes
anterior below; an internal, slightly convex and subcutaneous; the
posterior, which presents, in its superior part, a crest, the oblique
line of the tibia, and some rugosities. The borders separate the
surfaces. The anterior border, or crest of the tibia, is prominent in
its superior part; below it gradually disappears in passing towards the
internal aspect of the inferior extremity. The external and internal
borders separate the corresponding surfaces from the posterior one.

The superior extremity is thick, and expands in forming three
tuberosities: two lateral and an anterior. The anterior tuberosity,
situated at the superior part of the crest of the tibia, is very
prominent; for this reason the superior extremity is very much expanded
in the antero-posterior direction--hence it results that this diameter
is equal to the transverse, and sometimes even greater. In man, it is
the latter which is the larger. The anterior tuberosity is visible under
the skin.

The inferior extremity, less thick, is prolonged internally by a
prominence which corresponds to the internal malleolus of man. In
animals whose fibula is but slightly developed the tibia presents, on
the external part of its inferior extremity, a small prominence, which
replaces the fibular malleolus. The ruminants must, however, be
excepted, in which we find in this region a special bone, which certain
authors look on as the inferior part of the fibula (see p. 97). The
inferior surface of this extremity of the tibia is articular; and is in
contact with one of the tarsal bones, the astragalus. Because the
superior surface of this latter has the form of a pulley, a pulley much
more marked than that on the human astragalus, the corresponding surface
of the tibia, which has the opposite form, presents two lateral
cavities, separated by a median ridge, which is directed forwards and
slightly outwards; this ridge projects into the groove of the pulley.

=The Fibula.=--This bone, situated at the back of the external
surface of the tibia, is, as we have said, more or less developed. Its
superior extremity, or head, articulates with the external tuberosity
of the tibia. Its inferior extremity, when it exists--it is this
which disappears in animals which have the fibula incompletely
developed--forms a prominence which, placed on the external surface of
the inferior extremity of the tibia, articulates with the astragalus,
and recalls the external malleolus of man.

We have stated above that it is the inferior extremity of the fibula
which disappears when the bone is incompletely developed; it is
necessary to except the bat, in which the fibula, fairly well developed
at its inferior extremity, by which it articulates with the tibia, thins
off in its superior portion, and does not reach the corresponding
extremity of the latter. Further, as in this animal the surface of the
knee, which corresponds to the anterior surface of the same region in
other animals, is turned backwards, the result is that the fibula is
situated on the inner side of the tibia, instead of being placed on the
outer.


The Foot

The foot, in animals, as well as in man, is formed of three portions,
which, as we pass from the part which articulates with the leg towards
the terminal extremity, are: the tarsus, the metatarsus, and the toes.
These three portions are the homologues of the carpus, the metacarpus,
and the fingers, which, as we have already seen in the case of the hand,
are the osseous groups which form its skeleton. The tarsus is formed of
short bones, as the carpus is; these are, in man, seven in number. The
bones are arranged in two rows: one, the posterior, formed of two bones
superimposed--the astragalus, by which the tarsus articulates with the
leg, and the calcaneum, which forms the prominence of the heel; and an
anterior row formed of five juxtaposed ones--the cuboid, situated
externally, and the scaphoid internally, in front of which are found the
three cuneiforms. To the tarsus succeeds the metatarsus, whose form
reminds us very much of that of the metacarpals.

With regard to the toes, which we enumerate in proceeding from the most
internal to the most external, they are formed of phalanges, which are
three in number for the four outer toes; but the number is reduced to
two in the case of the first--that is, the so-called great-toe.

The bones of the tarsus are not seven in all animals; they are fewer in
ruminants and solipeds. We already know that, in the latter, the
metacarpals and the digits are equally reduced in number; the same is
the case for the metatarsals and the toes. We will analyze these
differences when dealing with the species individually.

When we studied the anterior limbs, we saw in passing from the
plantigrades to the digitigrades, and finally the ungulates, or
unguligrades, as the hand became hyperextended, the carpus was raised
and more and more removed from the ground. We shall establish the
existence of the same condition in the posterior limbs; in the
plantigrades the tarsus rests on the ground; in the digitigrades it is
removed from it; while in the unguligrades the distance which separates
it from the point of support is still more considerable; and it is,
indeed, necessary to imagine that if these latter were plantigrades,
would occupy the position on the ground which is indicated by Fig. 47.

In veterinary anatomy the tarsus is called the _ham_; a name we adopt
in conformity with usage, but which we cannot but regret, as in human
anatomy the ham is the region of the posterior surface of the knee.

The general arrangement of the region of the digits of the posterior
limbs in birds, presents some points of interest.

We shall merely say with regard to the metatarsus, that it is formed by
a single bone, which in the cock is furnished towards its inferior third
with a pointed process, the _spur_. At the inferior part, there is,
however, found another, which is but very slightly developed, and with
which the first phalanx of the innermost toe articulates.

The toes are, in the majority of species, four in number:[15] an
internal, which is directed backwards, and corresponds to the great-toe;
the others are directed forwards. This arrangement is constant in
grallatores (wading birds), gallinaceæ[16] (domestic fowls), and
raptores (birds of prey).

  [15] In spite of the fact that the custom is to designate the terminal
       portions of the foot of birds by the name of digits, we prefer to
       employ here the terms _foot_ and _toes_. In adopting this
       decision we believe we are acting according to a more didactic
       method. Homology of names should, in our opinion, always
       accompany homology of regions.

  [16] With regard to the gallinaceæ, we must add that in certain
       varieties the number of toes is five; those which are directed
       forwards are three in number; the internal one which passes
       backward, is double. The two toes which are the subject of this
       special arrangement are placed very close together, and are
       nearly always superimposed. This condition is found in the Houdan
       and Dorking breeds.

[Illustration: FIG. 47.--POSTERIOR LIMB OF THE HORSE PLACED IN THE
POSITION WHICH IT SHOULD OCCUPY IF THE ANIMAL WERE A PLANTIGRADE: LEFT
LIMB, EXTERNAL SURFACE.

1, Tibia; 2, astragalus; 3, calcaneum; 4, metatarsus; 5, first phalanx;
6, second phalanx; 7, third phalanx.]

In climbing birds (parrots, woodpeckers, and toucans), the innermost
toe is not only directed backward, but the external toe accompanies it
in that direction; consequently, there are two posterior and two
anterior toes. Sometimes they are all directed forwards; this
disposition is found in the martins. In some birds, the number of toes
is reduced to three: the cassowary shows this reduction; in others, the
number is still further diminished--the ostrich, for example, has but
two.

[Illustration: FIG. 48.--SKELETON OF THE FOOT OF A BIRD (THE COCK): LEFT
SIDE, EXTERNAL SURFACE.

1, Metatarsus; 2, spur; 3, rudimentary metatarsal; 4, first toe; 5,
second toe; 6, third toe; 7, fourth toe.]

Further, we find that, in general, the number of the phalanges
increases, when we examine the toes in commencing with the most internal
(Fig. 48): this has two; then the following one three; that which comes
next in order has four; and the most external toe has five. The
phalanges of this last are short; so that, although it is formed by a
larger number of bones, it is not the longest of the toes.


THE POSTERIOR LIMBS IN SOME ANIMALS.

=Plantigrades=: =Bear= (Fig. 33, p. 50).--The external iliac fossa is
very deep. The femur is longer than the bones of the leg; the great
trochanter does not reach the level of the head of the femur. The
fibula is well developed; it is united to the tibia at its superior and
inferior extremities only.

The foot, which, as in the case of the hand, rests on the ground by the
whole extent of its plantar surface, presents five toes; the shortest of
these is the internal--that is, the toe which corresponds to the
great-toe in man; the third and fourth are the longest, and they are
almost equal; there is a very slight difference in favour of the fourth,
which is slightly superior in dimensions to the third.

=Digitigrades=: =Cat=, =Dog= (Fig. 34, p. 52).--The external iliac
fossa, which looks outwards, is deep; the iliac crest is convex
anteriorly, the convexity is continued from one iliac spine to the
other.

[Illustration: FIG. 49.--PELVIS OF THE DOG, SEEN FROM ABOVE.

1, Iliac crest; 2, external iliac fossa; 3, sacrum; AA´, bi-iliac
diameter; BB´, bi-ischial diameter.]

In the dog, the distance which separates the anterior iliac spines is
less than that which separates the ischia (Fig. 49). On a skeleton which
we measured, the transverse diameter, the distance from the anterior
iliac spine of one side to that of the opposite side, was 8 centimetres,
whilst the distance which separated the ischia was 105 millimetres; on
another skeleton, the first measurement was 127 metres, and the second
was 146 millimetres. It seems to us unnecessary to multiply examples.

In the cat, the iliac spines are but slightly marked; the result is
that the iliac crest is almost confounded with the inferior and superior
borders of the ilium. The two diameters referred to above are almost
equal (Fig. 50).

We draw particular attention to what we have just noted in regard to the
transverse proportions of the iliac and ischiatic regions of the dog and
the cat. These relations are evidently of importance with regard to
shape, since the iliac crests and the ischia are noticeable beneath the
skin.

[Illustration: FIG. 50.--PELVIS OF A FELIDE (LION), VIEWED FROM ABOVE.

1, Iliac crest; 2, external iliac fossa; 3, sacrum; AA´, bi-iliac
diameter; BB´, bi-ischial diameter.]

In the dog, the shaft of the femur is slightly convex in front; but in
the cat it is straight. The borders of the shaft are slightly marked, so
that it is almost cylindrical. The _linea aspera_, less prominent than
in man, gains in width what it loses in elevation; it constitutes what
may almost be called a rough _surface_. This surface is narrower in its
middle portion than at its extremities, where it bifurcates to go
upwards to the two trochanters, and downwards to the two condyles. At
the superior extremity, the neck is short, the great trochanter reaching
almost to the level of the head of the femur; the digital _cavity_,
which is situated on the internal surface of the great trochanter, is
very deep. At its inferior extremity it projects strongly backward. The
trochlea is narrow; in the cat its two lips are equally prominent, while
in the dog the external is a little more elevated than the internal,
which on its part is a little thicker. The trochlea is still more
independent of the condyles than in the human femur; it is separated
from these latter by a slight constriction.

The knee-cap is long and narrow.

The tibia of the dog is slightly curved from before backward: it has the
form of an elongated S; this conformation is in great part due to the
very marked projection of the anterior tuberosity and of the superior
portion of the crest, which, a little below that tuberosity, turns
abruptly backwards, and thus describes a curve the concavity of which is
directed forward. The superior part of the external surface is very much
hollowed out.

The superior extremity is much thicker than the inferior one. It is not
only wide in the transverse direction, but is more especially extended
from before backwards; the prominence of the anterior tuberosity is the
cause of the elongation of this antero-posterior diameter. On the
posterior part of the external tuberosity is found a surface to which
the superior extremity of the fibula is applied.

The inferior extremity presents an articular surface, which is formed of
two lateral cavities, separated by a crest, which is directed obliquely
forwards and outwards. The internal part is prominent, and forms the
internal malleolus.

With regard to the fibula, it is united to the tibia by its extremities
and by the inferior half of its shaft. This latter is more expanded
below than in its upper part. The superior extremity is flattened from
without inwards. The inferior extremity projects beyond the articular
surface of the tibia, and forms the external malleolus, which, instead
of, as in man, descending further than the tibial malleolus, stops at
the same level, and even descends a little less than does the latter.

In the cat, the curve of the tibia is less pronounced; this is due to
the fact that the crest, instead of being concave in its middle portion,
is slightly convex anteriorly. The fibula, less flattened than that of
the dog, is united to the tibia by its extremities only, and is separate
in the rest of its extent.

The bones of the tarsus are seven in number, and arranged as in man,
with this difference (which is easily comprehended), that their general
relations are changed on account of the vertical direction of the
tarsus. For example, the astragalus, instead of being above the
calcaneum, is situated in front of it; the cuneiform bones, instead of
being situated in front of the scaphoid, are found below it, etc.

These animals have but four well-developed metatarsals; that which
corresponds to the great-toe is represented merely by a small
style-shaped bone, situate at the internal part of the region.

Nevertheless, we find this toe fully developed in some dogs.
Notwithstanding this, the bones which form it are, however, but
rudimentary, and much smaller than those of the innermost digit of the
fore-limb.

Sometimes it is double; this condition is demonstrable in individuals
belonging to breeds of large size. The median metatarsals are more fully
developed than the other bones of the same region which are next them.
Viewed as a whole, the metatarsal bones are a little longer than the
metacarpals; the result is that the distance which separates the tarsus
from the ground is a little greater than that which separates the carpus
from the plane on which the anterior limbs rest. The length of the
calcaneum still further exaggerates this difference, and, as in the
animals with which we shall occupy ourselves later on, the projection
which this bone forms is distinctly higher than that which is produced
by the pisiform.

The metatarsus, as a whole, is a little narrower than the metacarpus;
not only on account of the presence of a thumb in the anterior limb,
but, further, because the bones of this latter region are wider than
those of the corresponding part of the posterior limb.

The phalanges closely resemble those of the anterior limbs.

=Unguligrades=: =Pig= (Fig. 38, p. 58).--The pelvis in this animal
presents a few of the characters which we shall again meet with in the
ruminants and the solipeds; however, the posterior (or internal) iliac
spines are relatively more widely separated from one another than in the
latter. This arrangement reminds us of that found in the carnivora.

The femur presents nothing very special. The knee-cap is thick, and
ovoid in outline.

The fibula is completely developed, as in the carnivora; and is
connected with the tibia at both its extremities.

The tarsus consists of seven bones. The astragalus and the calcaneum
differ slightly from those of ruminants.

The foot, like the hand, has two median digits which rest on the ground
by their third phalanges; and an internal and an external digit, which
are removed from it. The metatarsals are a little longer than the
metacarpals.

[Illustration: FIG. 51.--PELVIS OF THE OX: SUPERIOR SURFACE.

1, Iliac crest; 2, external iliac fossa; 3, sacrum; AA´, bi-iliac
diameter; BB´, bi-ischiadic diameter.]

=Unguligrades=: =Sheep=, =Ox= (Fig. 39, p. 61).--The pelvis of ruminants
of this group closely resembles that of the horse, which we will study
later on (see p. 99). That which we must at once point out is that, with
regard to the ratio formed by a comparison of the bi-iliac and
bi-ischiatic diameters, it may be placed between the ratio obtained in
comparing those diameters in the pelvis of the carnivora and that of the
solipeds. Indeed, in the ruminants, the distance which separates the
ischia exceeds the width of one iliac only, and does not equal, as in
the felide, the total width of the anterior part of the pelvis (Fig.
51). In the skeleton of the ox, which forms part of the anatomical
museum of the École des Beaux-Arts, the bi-ischiadic diameter is 39
centimetres, whilst the width of one iliac crest is 29 centimetres, so
that, in contrast to that which we find in the dog, the width of the
ischiadic region is less than that formed in front by the addition of
the iliac crests.

The great trochanter is large, and extends beyond the level of the plane
in which the head of the femur is found.

In the ox, the linea aspera, instead of being a narrow crest, is spread
out, and forms in reality a surface; the posterior surface of the femur.
At the inferior and external part of this surface is situated a cavity
which surmounts the corresponding condyle, and is known as the
_supracondyloid fossa_. On the internal part of the same region there
are a series of tubercles, which, because of their position in relation
to the corresponding condyle, constitute the _supracondyloid crest_.

The internal lip of the trochlea is much thicker and much more prominent
than the external.

The details which we have just now examined in connection with the ox
are less marked in the sheep.

The trochlea, narrow as a whole, is clearly separate from the condyles
by a very marked constriction.

The patella, which is thickened in the antero-posterior direction, has
the shape of a triangular pyramid with the base upwards. Its posterior
surface, which articulates with the trochlea, presents an arrangement
which is adapted to the disposition of this latter--that is to say, the
surface which is in contact with the internal lip is larger than that
which articulates with the lip of the opposite side.

The tibia of the ox is proportionately shorter than that of the sheep.
The shaft of this bone is flattened from before backwards, in its
inferior half. The median crest of the articular surface of the inferior
extremity is the most prominent part of that region.

[Illustration: FIG. 52.--TARSUS OF THE OX: POSTERIOR LEFT LIMB,
ANTERO-EXTERNAL SURFACE.

1, Tibia; 2, coronoid bone of the tarsus; 3, superior articular surface
of the astragalus; 4, inferior articular surface of the astragalus; 5,
calcaneum; 6, cuboido-scaphoid bone; 7, great cuneiform bone--the small
cuneiform bone is situated at the back of the latter; 8, principal
metatarsal--the small, or rudimentary, metatarsal bone is very small; it
is situated at the back of the preceding, and is not to be seen in the
sketch. It would be visible if the view were directly lateral, but then
the superior and inferior articular surfaces of the astragalus would be
less apparent.]

The fibula is extremely atrophied. The shaft and superior extremity of
this bone are represented merely by a simple ligamentous cord, which is
sometimes ossified. There remains of the fibula, as a portion well and
distinctly developed, the inferior extremity only. This presents itself
under the form of a small bone situated in the region ordinarily
occupied by the inferior extremity of the outer bone of the leg--that is
to say, the external part of the inferior extremity of the tibia; this
little bone articulates with the astragalus and the calcaneum. Some
authors consider it to be a tarsal bone, and describe it under the name
of the coronoid bone of the tarsus (Fig. 52, 2). It is not, perhaps,
quite legitimate to describe it as a bone of this region, for it has
not a homologue in the tarsus of other animals. Its external surface is
rough; its superior border is furnished with a small pointed process
occupying a depression which is provided for it by the tibia. It reaches
lower down than the latter, and forms in this way a sort of external
malleolus, which frames, on the outer aspect, the mortise in which the
astragalus is maintained.

The tarsus, as a whole, has an elongated form; it is formed of five
bones: the astragalus, calcaneum, cuboid and scaphoid, which coalesce,
to form a single bone, and two cuneiform bones, which correspond to the
second and third cuneiform bones of the human foot. These cuneiforms are
called, from their size, commencing internally, by the names small and
great cuneiform.

The calcaneum is long and narrow; it is longer than that of the horse;
it is on the anterior and external part that the bone (coronoid tarsal
bone) which represents the inferior extremity of the fibula is situated.
It forms the prominence known as _the point of the ham_, a prominence
which is no other than the heel, which, in the unguligrades, is, as we
have already said, very far removed from the ground.

The astragalus, which is elongated in the vertical direction, has three
articular surfaces disposed in the form of trochleæ: a superior
trochlea, which is in contact with the skeleton of the leg, and which is
present in all animals; an inferior, which replaces the articular head
found on the anterior aspect of the astragalus in man; this articulates
with the portion of the scaphoido-cuboid that corresponds to the
scaphoid; and, lastly, a posterior trochlea with which the calcaneum
articulates. Of these three trochleæ, the superior is the most strongly
marked. Between this latter and the inferior is found, on the anterior
surface of the astragalus, a deep depression, which, during flexion of
the foot on the leg, receives a prominence which the inferior extremity
of the tibia presents in its median portion.

We can easily recognise the trochleæ which we have been discussing, in
the little bones which children use 'to play at bones'; these bones are
no other than the astragali of sheep.

We have already mentioned that the scaphoid and the cuboid are
ankylosed; they form by their union an irregular bone, on which the
astragalus and calcaneum are supported.

The cuneiforms articulate with the internal half of the superior
extremity of the principal metatarsal; the external half of this
metatarsal articulates with the portion of bone which represents the
cuboid.

The metatarsus is represented by a principal metatarsal, formed by the
coalescence of two metatarsals; we also find in this region a very small
rudimentary metatarsal.

The metatarsus is a little longer than the metacarpus; its transverse
measurement is a little less; on the other hand, it is a little thicker
in antero-posterior direction; from these two differences it results
that the body of the metatarsus is quadrilateral, whereas the metacarpus
presents only an anterior and a posterior surface.

The rudimentary metatarsal is a very small roundish bone, situated at
the back of the superior extremity of the principal metatarsal.

The phalanges closely resemble those of the anterior limbs;
nevertheless, the first and second phalanges differ from the latter in
the fact that they are a little longer and narrower.

At the back of the metatarso-phalangeal articulations, as in the
corresponding region of the anterior limbs, are found the sesamoid
bones. Such also exist at the articulations of the second and third
phalanges.

=Unguligrades=: =Horse= (Fig. 40, p. 64).--The pelvis of the horse
presents a general form which sharply differentiates it from that of the
carnivora; in fact, the ilium is twisted in such a way that the external
iliac fossa does not look outwards, but upwards. It results from this
twist that the anterior iliac spine, which we have seen to be directed
downwards in the carnivora, has become external; and this prominence is
much farther removed from the vertebral column than in the dog or cat.
On the other hand, the posterior iliac spine, which is directed upwards
in the carnivora, has become internal; it is also placed nearer to the
vertebral column, with the result that the distance which separates this
spine from that of the bone of the opposite side is proportionately
less.

The internal iliac spine, which is conical in shape, and curved upwards,
forms a prominence known as _the angle of the crupper_; the external
iliac spine, thick and provided with tuberosities, forms a
clearly-defined prominence; this is the angle of the _haunch_.

The iliac crest, extending directly from one spine to the other, is
curved, its concavity being turned upwards. The external iliac fossa,
which looks upward, is limited anteriorly by this crest, and is, like
the latter, slightly hollowed. The portion of the bone which connects
the ilium to the region occupied by the cotyloid cavity is extremely
narrow; posteriorly, the bone enlarges again to form the ischial and
pubic portions.

The tuberosity of the ischium, thick and curved upwards, but less so
than in the ox, forms the most prominent part of the posterior border of
the region of the thigh; this projecting portion, so sharply defined in
spare subjects, is known as the _point_ or _angle of the buttock_.
Contrary to what we have indicated in the case of the dog, the distance
which separates the ischiatic tuberosities is inconsiderable in
proportion to that which we find between the external iliac spine of one
side and that of the opposite. The bi-ischiatic diameter does not even
equal the width of one iliac bone measured at the level of its crest
(Fig. 53). On the skeleton of the horse in the École des Beaux-Arts, the
distance which separates the tuberosities of the ischia is 225
millimetres; that between the two spines of each iliac bone is 25
centimetres.

The anterior region of the crupper is thus much broader than that
occupied by the ischia.

The femur is relatively short. Its shaft is rectilinear, and does not
present the anterior convexity which is found on the human femur, and
which we indicated when discussing that of the dog. The shaft of the
bone, instead of being prismatic and triangular, presents four surfaces;
the anterior, internal, and external, almost pass into each other, being
separated one from the other merely by rounded and slightly marked
borders; the posterior surface, which is plane, replaces the linea
aspera, which in the horse, instead of presenting the appearance of a
crest, is considerably widened. The numerous irregularities which this
surface presents give insertion to the muscles which correspond to those
attached to the linea aspera.

Between this posterior surface and the external is found a rough
prominence which curves forward; this was designated by Cuvier the
_third trochanter_; it replaces the external branch of the superior line
of bifurcation of the linea aspera; other authors call it the
_infratrochanteric crest_, because it is situated below the great
trochanter. At the inferior part of the same region is found a deep
fossa, the borders of which are rough; this is the _supracondyloid
fossa_.

[Illustration: FIG 53.--PELVIS OF THE HORSE: SUPERIOR SURFACE.

1, Iliac crest; 2, external iliac fossa; 3, sacrum; AA´, bi-iliac
diameter; BB´, bi-ischiatic diameter.]

Between the posterior surface and the internal are found: above, the
lesser trochanter, which is long and rough; below, at the level of the
supracondyloid fossa, an equally rough surface known by the name of the
_supracondyloid crest_.

The superior extremity is flattened from before backwards. The neck is
not well marked. The great trochanter is very prominent, and projects
beyond the level of the head of the femur. We divide the great
trochanter into three parts: the summit, which is the most elevated
portion; the convexity, which is situated in front; and the crest,
formed by muscular impressions, situated outside and below the
convexity. The digital fossa is situated behind and below the summit of
the great trochanter. With regard to the lesser trochanter, it is placed
so far down that it really forms part of the shaft of the bone, with
which, besides, we have described it.

On the inferior extremity of the femur are two condyles and a trochlea;
the condyles are clearly separated from this latter by a marked
constriction.

The trochlea is directed with a slight obliquity downwards and inwards;
its internal lip is much thicker and more prominent than the external;
this is, accordingly, a condition exactly the opposite of that which
characterizes the corresponding region of the human femur.

The knee-cap is lozenge-shaped; its superior angle projects upward, and
produces a prominence at the part which corresponds to the base of the
human patella, the part which is here the thickest portion of the bone.
Its anterior surface is convex and rough. Its posterior surface presents
two lateral articular facets, separated by a crest; this surface is in
contact with the trochlea of the femur, and, as it is the internal lip
of the latter which is the more developed, it results therefrom that the
internal articular surface of the knee-cap is larger than the external.

The knee-cap contributes to the formation of the region of the posterior
limb which is called the _stifle_.

The tibia is large in its upper portion; in its inferior part it is
flattened from before backwards. The posterior surface of the shaft
presents an oblique line, below which are found vertical rough lines for
the insertion of muscles. The external surface is hollowed out in its
upper part. The anterior tuberosity of the tibia rises just to the level
of the flat articular surface; it is hollowed in its median portion by a
vertical groove of elongated form, which receives the ligament that
binds the knee-cap to the tibia. The external tuberosity is more
prominent than the internal; in it is found a groove for the passage of
the anterior tibial muscle.

The inferior extremity, flattened from before backwards, presents a
surface which is moulded on the trochlea of the astragalus; the median
crest of this surface is thick, and descends lower posteriorly than the
tuberosities which are situated on the external and internal aspects of
this extremity.

Of the two tuberosities, that which is internal is comparable to the
internal malleolus of man, the one on the outer side forms a sort of
external malleolus; but this latter here belongs to the tibia, and not
to the fibula.

The fibula, in fact, does not reach the inferior extremity of the tibia;
it is a poorly developed bone, elongated and terminating inferiorly in a
point, at the middle of the shaft of the tibia or at its lower third.
Its superior extremity, which is slightly expanded, articulates with the
tuberosity which occupies the outer aspect of the corresponding
extremity of the tibia.

The bones of the tarsus are six in number: the calcaneum and astragalus
form the upper row; the cuboid, scaphoid, and two cuneiforms form the
lower (Fig. 54).

The astragalus has not, as in ruminants, an inferior trochlea for
articulation with the scaphoid; this portion of the bone presents a
surface which is slightly convex. It articulates with the tibia by a
trochlea that occupies not only the superior surface, but also the
anterior. This trochlea, which is directed slightly obliquely downwards
and outwards, has a very pronounced form; its lips, which are extremely
prominent, determine by their anterior part one of the features which we
recognise on the anterior aspect of the _ham_--a feature which is still
more accentuated when the metatarsus (_canon_) is extended on the leg.
On the internal surface of the astragalus is found a tubercle, which
forms a projection in the corresponding region of the ham.

The calcaneum, which is not quite so long as that of the ox, forms by
its summit a prominence which is called _the point of the ham_.

The cuboid is small; the scaphoid is large, and flattened from above
downwards. Of the two cuneiforms, the more external is the larger; it
closely resembles the scaphoid; it is flattened from above downwards as
is the latter; but it is a little smaller in size. The small cuneiform,
which occupies the inner side of the tarsus, is the smallest bone in
this region; it is sometimes divided into two parts; this raises the
number of the cuneiforms to three, and that of the bones of the tarsus
to seven.

[Illustration: FIG. 54.--TARSUS OF THE HORSE: LEFT POSTERIOR LIMB,
ANTERIOR SURFACE.

1, Tibia; 2, internal tuberosity of the inferior extremity of the tibia
(homologue of the internal malleolus of man); 3, external tuberosity of
the inferior extremity of the tibia (homologue of the external
malleolus); 4, median crest lodged in the groove of the pulley of the
astragalus; 5, pulley of the astragalus; 6, internal tuberosity of the
astragalus; 7, calcaneum; 8, cuboid; 9, scaphoid; 10, great cuneiform,
the small cuneiform is placed behind this latter; 11, principal
metatarsal; 12, external rudimentary metatarsal. The internal
rudimentary metatarsal, being more slender than the external, does not
appear in the figure.]

The bones of the metatarsus and the phalanges are equal in number to the
corresponding bones in the anterior limbs; they are formed on a type
analogous to that of these latter. Accordingly, we shall merely indicate
the differences which characterize them.

The principal metatarsal is longer than the metacarpal of the same
class; its shaft is more cylindrical; its inferior extremity is somewhat
thicker. The external rudimentary metatarsal is better developed than
the internal; in the metacarpus the reverse is the case.

The phalanges so far resemble those of the anterior limb that, as
differential characters, we need point out only the following: the first
phalanx of the hind-foot is a little shorter than that of the fore-foot;
its inferior extremity is a little narrower, and its superior extremity
a little thicker. The second phalanx is a little less expanded
laterally.

The difference in appearance which the three phalanges, anterior and
posterior, respectively present are to be borne in mind; for they are
correlated to the general form of the fore and hind feet. We will
establish this point when we come to study the hoof (see Figs. 101 and
102, p. 257). In the fore-foot the ungual phalanx has its inferior
surface limited externally by a circular border, while the same bone of
the hind-foot has this surface a little narrower, more concave, and
limited by two curved borders which unite anteriorly to form an
angle--an arrangement which gives to the general outline of this region
the form of the letter V.


Articulations of the Posterior Limbs

=The Coxo-femoral Articulation.=--The head of the femur is received in
the cotyloid cavity; these are the osseous surfaces in contact in this
articulation. They are maintained in position by a fibrous capsule and a
round ligament. To this latter is found attached, in the horse, a
fasciculus which, commencing, as does the round ligament, at the
depression on the head of the femur, emerges from the cotyloid cavity by
the notch which is present in its circumference, and is attached to the
anterior border of the pubes, to blend with the tendon of the rectus
muscle of the abdomen. This is the pubio-femoral ligament.

The movements which this joint permits are the same in the quadrupeds as
in man, but less extensive. They are: flexion and extension, abduction
and adduction, the two latter being much more limited than the former.
There is also rotation.

By flexion, the inferior extremity of the femur is directed forwards;
the bone of the thigh then takes a more oblique direction than the
normal. This movement takes place, for example, when the animal carries
forward one of its hinder limbs. Extension, which takes place in an
inverse sense, is produced when the foot is fixed on the ground, while
the body is projected forward. It is also produced in the action of
kicking.

As for the lateral movements--viz., abduction and adduction--they are
less extensive than the preceding movements. The absence of the
pubio-femoral ligament in other quadrupeds than the horse explains why
in them abduction is less limited than in the latter. Indeed, it is the
tension of this ligament, occasioned by the abduction of the thighs,
which arrests more quickly the movement in question.

=Articulation of the Knee.=--This articulation, as in man, is formed by
the femur, the patella, and the tibia.

In the horse the ligament of the patella is not single, but consists of
three parts, designated, on account of their position, by the respective
names of external, internal, and median patellar ligaments. The two
former come from the angles on the corresponding borders of the
knee-cap; the median springs from the anterior surface and inferior
angle of the same bone. They all three pass to their termination on the
anterior tubercle of the tibia. The external ligament is the strongest,
and the internal ligament the least developed.

In the dog, the cat, the pig, and the sheep, the patellar ligament
consists of a single band. The articulation is further strengthened on
the sides by lateral ligaments--an internal and an external.

With regard to the principal movements, these are flexion and extension,
to which may be added movements of rotation of limited extent. In
flexion, the leg bends on the thigh; its inferior extremity is directed
upwards and backwards; the angle which the tibia naturally forms with
the femur becomes less obtuse.

But it should be understood that one part of this description--that
which has relation to the leg--holds good only when the femur is in its
normal condition, or in flexion. Indeed, at the close of the movement in
which, during a step, the foot is in contact with the ground--that is,
at the termination of the resting stage--the inferior extremity of the
tibia is directed backwards. But the femur is then in a state of
extension, and in regard to this latter the attitude of the leg is
unchanged.

[Illustration: FIG. 55.--EXTENSION OF THE LEG: RIGHT POSTERIOR LIMB OF
THE HORSE, EXTERNAL SURFACE. (AFTER A CHRONOGRAPHIC STUDY BY PROFESSOR
MAREY.)]

At this moment, notwithstanding the direction, which recalls that which
it has at the time of flexion, the leg is not bent on the thigh; on the
contrary, it is almost in the line of its continuation (Fig. 55). As we
have done in connection with the articulations of the anterior limbs, we
borrow this figure from the interesting chronophotographic studies of
Professor Marey.[17]

  [17] E. J. Marey, 'Analysis of the Movements of the Horse by the
       Chronophotograph' (_La Nature_, June 11, 1898).

=The Tibio-tarsal Articulation and of the Bones of the Tarsus.=--In the
region which veterinary anatomists call the ham, the articulations of
the leg and foot alone call for special study in the case of the horse.
The articulations of the bones of the tarsus, and of these with the
metatarsus, do not offer any interest with regard to mobility, this
being almost wholly absent at that level.

The leg and the astragalus, in a general way, are placed in contact by
such articular surfaces that the resulting joint, which is a true hinge,
permits movements of flexion and extension only. Indeed, as we have
indicated above, the tibia is furnished, on the inferior surface, with a
crest that fits into the deep groove which is situated on the
corresponding surface of the astragalus.

During flexion, the anterior surface of the foot tends to approach the
anterior surface of the leg, the angle formed by these two segments
becoming more and more narrowed. The displacement in the opposite
direction characterizes extension.

In other quadrupeds, the articulations which bind together the bones of
the tarsus possess a little more freedom of movement. The shape of these
bones, and particularly the shape of the surfaces of the astragalus,
which are in contact with them, allow movements in this region, in the
case of the dog and cat, which, without being so extensive as those of
the human foot, in the subastragaloid articulation, nevertheless, recall
the mobility which we find in the human species at this level--that is
to say, rotation, abduction, and adduction of the foot.

As for the articulations of the metatarsus with the phalanges, and of
the phalanges with one another, they resemble those of the anterior limb
too closely that it should be necessary to study them here. Such a study
would be, in this case, but a repetition (see p. 76, a description of
the articulations in question).


THE HEAD IN GENERAL, AND IN SOME ANIMALS IN PARTICULAR

When we compare, by the examination of one of their lateral aspects, the
skull of man and the same region in other mammals, it is easy to observe
that the relative development of the cranium and face is entirely
different. In the case of man the cranium is large, and the face
relatively small; in animals the face is proportionally much more highly
developed. The measure of the facial angle permits us to note these
differences, and the figures relative to the value of this angle are
sufficiently demonstrative to induce us to indicate those which are, in
a general way, connected with some of the forms in individuals which
here occupy our attention. In the first place, we must remember that the
angle in question is more acute, as the cranium is less developed in
proportion to the facial region (Figs. 56 and 57). It is especially to
this character that we wish to draw attention.

  Man      70°-80°
  Cat      41°
  Dog      28°-41°
  Sheep    20°-25°
  Ox       18°-20°
  Ass      12°-16°
  Horse    11°-13°

Besides, in animals the cranium is very prominent superiorly, and the
face, more or less elongated, is sharply projected downwards and
forwards; in man the cranial region occupies not only the superior, but
also the posterior part; the face is short and of a compact form. The
human head, in its general aspect, may be compared to a sphere, while
the skull of the quadrupeds presents the aspect of a quadrangular
pyramid, with the base turned upwards and the summit at the incisor
teeth.

=Direction of the Head.=--Before entering on the study of the bones of
the head, it is necessary, in our opinion, to agree as to the position
in which we shall suppose it to be placed.

The question may seem to be one of little importance; nevertheless, it
cannot be regarded as indifferent, since authors are not all agreed on
this subject.

Some suppose it to be placed vertically--that is, with the incisor teeth
turned directly downwards. Others, on the contrary, suppose it to be
placed horizontally, resting on the whole length of the lower jaw, the
face being then turned upwards. These two extreme methods of arrangement
appear to us to possess inconveniences--at least, for comparison with
the human head.

[Illustration: FIG. 56.--HUMAN SKULL: MEASURE OF THE FACIAL ANGLE BY THE
METHOD OF CAMPER. ANGLE BAC = 80°.

The internal wall of the cranial cavity is marked by the dotted line.]

[Illustration: FIG. 57.--SKULL OF THE HORSE: MEASURE OF THE FACIAL ANGLE
BY THE METHOD OF CAMPER.[18] ANGLE BAC = 13°.

The internal wall of the cranial cavity is shown by the dotted line.]

  [18] We have indicated on this sketch of the skull of the horse the
       facial angle measured by the method of Camper, in order that the
       correspondence with Fig. 56 may be more complete. But it is
       certain that the procedure here employed is in practice not
       satisfactory, since the apex of the angle, as we can demonstrate,
       is found to be situated within the contour of the head, and that,
       consequently, it is rather difficult to localize it precisely in
       the case of a given skeleton. Further, because of the absence of
       the base of the nose in the complete skull, the auriculo-nasal
       line cannot be accurately fixed. It would be the same for most
       other animals. This is why the method employed for these latter
       is preferably that of Cuvier, or, again, that of Cloquet. In the
       former, the apex of the angle of Camper is transferred to the
       free border of the upper incisors, but these teeth may be absent,
       and, on the other hand, ruminants are destitute of them. In the
       second, the same apex is placed at the alveolar border, and the
       angle then becomes fairly easy to appreciate.

Indeed, if, when the head is vertical, the same regions of the face
(forehead, nose) are, in the case of animals as well as man, turned
forward, the lower jaw ceases to merit its appellation, as it is then
situated, not below, but behind the upper. Furthermore, if this
position is chosen, for example, for modelling or drawing, it cannot be
obtained without difficulty when we have to deal with an isolated piece
of the skeleton, on account of the absence of equilibrium, which it is
necessary to obviate. It is true that the question of convenience should
not take precedence of all others, and it suffices for us in this
connection to recall, in regard to the human pelvis, that, although the
older anatomists used to represent it as resting commodiously on the
three angles which terminate it at its lower part (ischial tuberosities
and coccyx), this attitude being false, it is customary now to incline
the superior aspect forwards, inasmuch as this arrangement more nearly
conforms to reality, in spite of the fact that it is a little more
difficult so to dispose an isolated pelvis. Further, to return to the
head; if its vertical direction can be demonstrated, for example, in
many horses, it is not sufficiently general to be adopted as the classic
position.

In regard to the facility of placing in position, the horizontal
direction is certainly to be preferred; but this is also far removed
from the natural position in the animal while in the state of repose. On
the other hand, the mind is not satisfied with the idea that certain
regions of the face, such as the nose and the forehead, are then
directed upwards. And yet it is necessary to come to a decision, seeing
that what we are now investigating applies also to the position to which
it is necessary to give the preference in placing the skeleton of the
head when we wish to draw it in profile. That which we adopt is a
compromise, but to us it seems more rational.

The position of the head of the horse, to be normal, should be such as
to give it an inclination of 45°. In this case the lower jaw is still
posterior; and, for this reason, we see in adopting this position some
inconveniences from a didactic point of view. Accordingly, we will
suppose the head brought a little nearer to the horizontal, and this,
from the imaginative point of view, has certainly an advantage which we
cannot afford to neglect when addressing artists.

Indeed, let us suppose that to a clay model of a human head we wish to
give the aspect of the head of a quadruped. We should elevate the
occiput; and then, taking hold of the lower part of the face, we should
lengthen it, not in a direction precisely antero-posterior, but
downwards and forwards. It is obviously this latter procedure which, on
the other hand, is carried out when a person wishes to give to his own
face some resemblance to the muzzle of a quadruped.

It is true that, in the position we have adopted, the face is directed
obliquely downwards and forwards, and that there may result a certain
confusion in describing the position of its different parts. On
this account, with the object of not making complications, we
purpose, for the present, to substitute, for example, for the term
'antero-superior'--which when speaking of the position of the forehead
and nose would be more exact--the term 'anterior,' which is sufficiently
comprehensible. The mouth will be, for the same reason, referred to as
being situated at the inferior part of the face, and not the
antero-inferior.

=The Skull.=--The elevation of the cranial region becomes especially
appreciable when we examine the occipital bone. Before verifying this
fact, it is not superfluous to recall the general arrangement which this
bone presents in the human skull. A portion of the occipital bone
occupies the base of the skull; but this base in man is horizontal; to
this region succeeds the shell-shaped portion of the occipital bone,
which, passing vertically upwards, forms with the preceding portion an
angle situated at the level of the external occipital protuberance, and
of the curved line which starts from it on each side. In animals a
portion of the occipital bone is horizontal, it is true; but this bone
being sharply bent at the level of the occipital foramen and condyles,
the result is that the portion which surmounts these latter looks
backwards, and is limited above by the external occipital protuberance,
which forms the culminating point of the skull; this point is situated
between the ears.

[Illustration: FIG. 58.--SKULL OF ONE OF THE FELIDÆ (JAGUAR): LEFT
LATERAL ASPECT.

1, Posterior surface of the occipital bone; 2, external occipital
protuberance; 3, condyle of the occipital bone; 4, jugular process; 5,
parietal bone; 6, frontal bone; 7, orbital process; 8, orbital cavity;
9, squamous portion of the temporal bone; 10, external auditory canal,
in front of which is situated the zygomatic process; 11, tympanic bulla;
12, superior maxillary bone; 13, intermaxillary or incisor bone; 14,
nasal bone; 15, anterior orifice of the nasal cavity; 16, malar bone;
17, ungual or lachrymal bone; 18, inferior maxillary bone; 19, condyle
of the inferior maxillary bone; 20, coronoid process; 21, incisor teeth;
22, canine teeth; 23, molar teeth.]

[Illustration: FIG. 59.--SKULL OF THE LION: LEFT LATERAL ASPECT.

This figure is intended to show that in the lion the contour of the face
between the nasal bones and the cranial region is more flattened than in
other felidæ, such as the tiger, jaguar, panther, and domestic cat. This
difference is shown by comparison of this figure with the preceding one
(Fig. 58). We are indebted to M. Tramond, the well-known naturalist, for
the indication of this differential character which, from the artistic
plastic point of view, is one of real interest.]

This protuberance, prolonged on each side by the superior curved line of
the occipital bone, is so much the more prominent as this bone bends
sharply a second time, so as to form a third portion, which, looking
forwards, forms part of the anterior aspect of the skull, and proceeds
to articulate with the parietals. On this third portion is found a crest
which, proceeding from the occipital protuberance, is continuous in
front with the parietal crests, to which we will again refer in speaking
of the parietal bones.

On the inferior surface of the human occipital bone are found, at the
level of, and external to, the condyles two bony elevations which bear
the name of _jugular eminences_. They are long in quadrupeds, and
constitute what are designated by some authors the _styloid processes_,
but they must not be confounded with the processes of the same name
which in the case of man form part of the temporal bone. These processes
are very highly developed in the pig, horse, ox, and sheep.

In the ox, the occipital bone is deprived of the protuberance, and is
not bent on itself in the anterior portion, neither does it form the
most salient part of the skull; this latter, which is situated at the
level of the horns, belongs to the frontal bone. In the pig, also, the
occipital bone is not bent upon itself in its anterior portion, but
forms the summit of the head. The occipital protuberance, hollowed on
its posterior surface, rises vertically, and rests upon the parietal
bone, with which it forms an acute angle.

The parietals, two separate bones in the dog and the cat, but fused in
the median line in the ox, sheep, and horse, are of special interest in
regard to the two crests which, in the carnivora, and also in the pig
and the horse, occupy their external surface, and, after diverging from
one another, are continued by a crest which crosses the frontal bone
and ends at the external orbital process of the latter bone.

These crests, known as the _parietal_ or _temporal crests_, recall both
in position and relations the temporal curved line of the parietal bone
of man. They contribute, as in the case of the latter, to the formation
of the boundaries of the temporal fossa.

[Illustration: FIG. 60.--SKULL OF THE DOG: LEFT LATERAL ASPECT.

1, Posterior surface of the occipital bone; 2, external occipital
protuberance; 3, occipital condyle; 4, jugular process; 5, parietal
bone; 6, frontal bone; 7, orbital process; 8, orbital cavity; 9,
external auditory canal, in front of which is found the zygomatic
process; 10, tympanic bulla; 11, superior maxillary bone; 12,
intermaxillary or incisor bone; 13, nasal bone; 14, anterior opening of
the cavity of the nasal fossæ; 15, malar bone; 16, lachrymal bone; 17,
inferior maxillary bone; 18, condyle of the inferior maxillary bone; 19,
coronoid process; 20, incisor teeth; 21, canine teeth; 22, molar teeth.]

In the carnivora, these crests are situated, throughout their whole
length, in the median line, the temporal fossæ being, accordingly, as
extended as they possibly can be. In certain species, the development of
these crests is such that they form by their union a vertical plate,
which, in separating the two temporal fossæ, gives them a greater depth.
In the pig, the parietal crests, analogous in this respect to the
temporal curved lines of the parietal bones of man, are separated by an
interval, proportionately less extended, however, than that of the human
skull. The parietal bone in the ox and the sheep does not enter into the
formation of the anterior surface of the skull; it is formed by an
osseous plate, narrow and elongated transversely, which, with the
occipital bone, constitutes the base of the region of _the nape of the
neck_. It is bent upon itself at the level of its lateral portions so as
to occupy the temporal fossa.

The anterior surface of the frontal bone, which is depressed in the
median line in the dog, but plane in the horse, is limited by two
crests, which, situated on the prolongation of the parietal crests,
diverge more and more from one another in proportion as they occupy a
lower position. This surface terminates externally in two processes,
which are the homologues of the external orbital processes of the human
frontal bone.

The superior border of these orbital processes, situated on the
prolongation of the corresponding parietal crests, contributes to limit
the temporal fossa. Each of these orbital processes terminates in the
following manner: In the bear, dog, cat, and pig, in which the orbital
cavities are incompletely bounded by bone, this process, slightly
developed, is not in connection, by its inferior extremity, with any
other part of the skeleton of the region. In the ox and the sheep, it
articulates with a process of the malar bone. In the horse, it
articulates with the zygomatic process of the temporal bone. The
inferior margin of this process forms a part of the boundary of the
anterior opening of the orbital cavity.

The supra-orbital foramen, which does not exist in carnivora, occupies
in the horse the base of the orbital process. In the ox, it is situated
a little nearer the middle line; and its anterior orifice opens into an
osseous gutter which is directed upwards towards the base of the horn,
while inferiorly it meets the inferior border of the frontal bone; in
the sheep this groove is but slightly developed. In this latter, as in
the ox, it is the frontal bone which forms the most elevated portion of
the skull. In fact, being bent upon itself at a certain level, its
external surface is formed of two planes: one, posterior, which is
inclined downwards and directed backwards; the other, anterior, is also
inclined downwards, but with a forward obliquity. At the union of these
planes the bone forms an elbow, on either side of which are found the
osseous processes on which the horns are mounted.

[Illustration: FIG. 61.--SKULL OF THE PIG: LEFT LATERAL ASPECT.

1, Occipital bone; 2, condyle of the occipital; 3, jugular process; 4,
parietal bone; 5, parietal crests; 6, frontal bone; 7, orbital process;
8, orbital cavity; 9, external auditory canal; 10, zygomatic process;
11, superior maxillary bone; 12, intermaxillary or incisor bone; 13,
nasal bone; 14, anterior orifice of the cavity of the nasal fossæ; 15,
malar bone; 16, lachrymal bone; 17, inferior maxillary bone; 18, condyle
of the inferior maxillary bone; 19, incisor teeth; 20, canine teeth; 21,
molar teeth.]

In the bear, the anterior margin of the frontal bone is prolonged by two
small tongues of bone, which, descending on the lateral borders of the
nasal bones, articulate with the superior half of the latter.

The temporal bone is, as in man, furnished with a squamous portion,
from which springs the zygomatic process, which is directed towards the
face, to terminate in the following manner: in the carnivora, the pig,
and ruminants, it articulates with the malar bone by its inferior
border; in the horse, it insinuates itself as a sort of wedge between
the malar bone and the orbital process of the frontal bone, with which
it articulates, as we have already pointed out, and contributes, by a
portion situated in front of this articulation, to form the boundary of
the anterior opening of the corresponding orbital cavity. As in man, the
zygomatic process arises by two roots: one, transverse, behind which is
situated the glenoid cavity of the temporal bone; the other,
antero-posterior, which proceeds to join above with the superior curved
line of the occipital bone.

Behind the glenoid cavity is found the external auditory canal, and,
further back still, the mastoid process. This latter, but slightly
developed in the carnivora, a little more so in the ruminants, and still
more in the horse, has its external surface traversed by a crest, _the
mastoid crest_, which, after becoming blended with the antero-posterior
root of the zygomatic process, proceeds with this latter to join the
superior occipital curved line.

Below the auditory canal is situated a round prominence, highly
developed in carnivora; this is _the tympanic bulla_, also called _the
mastoid protuberance_; it is an appendage of the tympanum.


The Face

The bone of this region, around which all the others come to be grouped,
is, as in man, the superior maxillary. The relations of this maxillary
with the neighbouring bones is not exactly the same in all animals; for
example, in the ox, sheep, and horse, in which the bones of the nose are
wide in their upper part, and in which the lachrymal bone, which is very
highly developed, encroaches on the face, the superior maxillary does
not meet the frontal bone; it is separated from it by the above-named
bones. It unites with it, on the other hand, in the dog and the cat. In
the bear, it is separated from the bones of the nose by a small tongue
of bone which springs from the anterior border of the frontal--a
process which we have noticed in connection with this latter.

[Illustration: FIG. 62.--THE SKULL OF THE OX: LEFT LATERAL ASPECT.

1, Occipital condyle; 2, jugular process; 3, parietal bone; 4, frontal
bone; 5, osseous process, which serves to support the horn (horn-core);
6, orbital cavity; 7, external auditory canal, in front of which is
found the zygomatic process; 8, temporal fossa; 9, superior maxillary
bone; 10, intermaxillary or incisor bone; 11, nasal bone; 12, anterior
orifice of the cavity of the nasal fossæ; 13, malar bone; 14, lachrymal
bone; 15, inferior maxillary bone; 16, condyle of the inferior maxillary
bone; 17, incisor teeth; 18, molar teeth.]

In the pig, ox, sheep, and horse, the external surface is traversed, to
a greater or less extent, by a crest which is situated on the
prolongation of the inferior border of the malar bone. This crest, which
is straight in the horse, but curved with its convexity upwards in the
ox and the sheep, is known as _the maxillary spine_ or _the malar
tuberosity_: it gives attachment to the masseter muscle, and, in the
horse, is distinctly visible under the skin. It does not exist in the
carnivora. On the same surface is situated the sub-orbital foramen.

The inferior border is hollowed out into alveoli, in which are implanted
the superior molar and canine teeth. This border is prolonged forwards
from the alveolus, which corresponds to the first molar tooth, to
terminate, after a course more or less prolonged, at the alveolus of the
canine. This space, more or less considerably expanded, which thus
separates these teeth is called the _interdental space_; but this
denomination is not applicable to ruminants, because these latter
possess neither canine nor incisor teeth in the upper jaw (see p. 125,
dentition of the ox and sheep). The superior maxillary bone of one side
and that of the opposite side do not meet in the median line in the
region which corresponds to the incisor teeth; they are separated by a
bone which, in the human species, is present only at the commencement of
life, and afterwards coalesces with the maxilla; this is the
intermaxillary or incisor bone. This bone, which is paired, is formed of
a central part, which bears the superior incisor teeth; it is prolonged
upwards and backwards by two processes: one, external, which insinuates
itself between the superior maxillary and the nasal bone, except in the
sheep, in which it remains widely separated from the latter; the other,
internal, which is united to that which belongs to the bone of the
opposite side to form part of the floor of the cavity of the nasal
fossæ; the external border of this process, which is separated from the
body of the bone by a notch, forms the internal boundary of the
corresponding _incisor opening_ or the _incisor slit_. Owing to the
absence of superior incisors in ruminants, the intermaxillary bone
presents no alveoli.

The malar bone, and the os unguis or lachrymal, are more or less
developed according to the species considered. With regard to the malar
bone, it is most important to notice the part which it takes in the
formation of the zygomatic arch, and that its inferior border
contributes to form the crest to which is attached the masseter muscle.

As for the nasal bones, they present differential characters which, as
they affect the form of the region which they occupy, are worthy of
notice.

[Illustration: FIG. 63.--SKULL OF THE HORSE: LEFT LATERAL ASPECT.

1, Posterior surface of the occipital bone; 2, external occipital
protuberance; 3, occipital condyle; 4, jugular process; 5, parietal
bone; 6, frontal bone; 7, orbital cavity; 8, zygomatic process of the
temporal bone; 9, external auditory canal; 10, mastoid process; 11,
superior maxillary bone or _maxilla_; 12, intermaxillary or incisor
bone; 13, nasal bone; 14, anterior orifice of the cavity of the nasal
fossæ; 14´, malar bone; 15, lachrymal bone; 16, inferior maxillary bone
or _mandible_; 17, inferior maxillary fissure; 18, condyle of the
inferior maxillary bone; 19, coronoid process of the inferior maxillary
bone; 20, incisor teeth; 21, canine teeth; 22, molar teeth.]

Their dimensions in length are proportional to those of the face. Very
small in man, they are more developed in carnivora. We recognise in the
latter the two curves which characterize them in the human species, and
which we clearly notice when we view them on one of their lateral
aspects: a concavity above, and a convexity below. These curves are more
or less accentuated--very strongly marked in the bulldog, and scarcely
at all in the greyhound. Moreover, in the carnivora also the nasal bones
are wider below than above, and form, by their junction, a semicircular
notch which limits, in its superior portion, the anterior opening of the
cavity of the nasal fossæ. In the horse they present an opposite
arrangement with regard to their dimensions in width; broad above, each
terminates below by forming a pointed process which, separated from the
intermaxillary bones, is prolonged in front of the nasal orifice.

The inferior maxillary bone is, as in man, formed of a body and two
branches. But among the many special characteristics of form and size
which sharply differentiate it from the human bone, one detail must be
indicated; this is the absence of a mental prominence. Hence it results
that the anterior border of the body of the lower jaw, instead of being
directed obliquely downwards and forwards, is, on the contrary, oblique
downwards and backwards, and that in certain animals this border is
actually found almost exactly on the prolongation of the inferior border
of the body of the bone.

On the external surface of the body are found the three mental foramina.
The superior border is hollowed out by alveoli.

With regard to the branches (_rami_), they terminate in two processes:
one, the posterior, is the condyle; the other, situated more forwards,
is the coronoid process, which gives insertion to the temporal muscle.
These two processes are separated by the sigmoid notch.

For reasons which we will explain further on (see p. 127, movements of
the lower jaw), the condyle presents differences of form. In the
carnivora, it is strongly convex from before backwards, expanded
transversely, and firmly mortised in the glenoid cavity of the temporal
bone; in the ruminants, it is less convex from before backwards, it is
more slightly concave in the transverse direction; in the rodents--we
give as an example the hare (Fig. 64)--the condyle is still convex from
before backwards, but it is flattened from without inwards.

In the animals in which the muscles of mastication are very highly
developed, and especially in the carnivora, the osseous regions occupied
by these muscles are more extensive and more deep than in the human
species. The length of the coronoid process, the depth of the temporal
fossa, the extent of the zygomatic arch, the appearance of the external
surface of each of the rami of the lower jaw, deeply hollowed out for
accommodation of the masseter, and to provide extensive surfaces of
insertion for this muscle, are sure proofs furnished by the skeleton of
the occasionally enormous development of the muscles of mastication.

In the carnivora, a rather strong process, which is directed backwards,
occupies the angle of the inferior maxilla; it is, accordingly, situated
below the region of the condyle.

[Illustration: FIG. 64.--SKULL OF THE HARE: LEFT LATERAL ASPECT.

1, External occipital protuberance; 2, occipital condyle; 3, parietal
bone; 4, frontal bone; 5, orbital process; 6, orbital cavity; 7,
zygomatic process; 8, external auditory canal; 9, superior maxillary
bone; 10, intermaxillary or incisor bone; 11, nasal bone; 12, anterior
opening of the nasal fossa; 13, malar bone; 14, inferior maxillary bone;
15, condyle of the inferior maxillary bone; 16, incisor teeth; 17, molar
teeth.]

The teeth which the jaws carry vary in number, and even in appearance,
according to species; it is useful to note their differences. In order
to establish the nature of these latter more effectively, we will first
recall the fact that in man the teeth, thirty-two in number, are equally
distributed between the jaws, and are divided into incisors, canines,
and molars, of which the arrangement is thus formulated:

  5_m._  1_c._  2_i._ | 2_i._  1_c._  5_m._
  --------------------+-------------------- = 32.[19]
  5_m._  1_c._  2_i._ | 2_i._  1_c._  5_m._

  [19] _I.e._, _i_, incisors; _c_, canines; _m_, molars.

We also note that the incisors are edged, the canines are pointed, and
that the molars, cubical in shape, have their surface of contact
provided with tubercles.

The teeth of the cat are thirty in number; they are thus arranged:

  4_m._  1_c._  3_i._ | 3_i._  1_c._  4_m._
  --------------------+-------------------- = 30.
  3_m._  1_c._  3_i._ | 3_i._  1_c._  3_m._

Those of the dog number forty-two:

  6_m._  1_c._  3_i._ | 3_i._  1_c._  6_m._
  --------------------+-------------------- = 42.
  7_m._  1_c._  3_i._ | 3_i._  1_c._  7_m._

In these animals, the incisors, such as are not damaged by use, are
furnished, on the free border of their crown, with three tubercles, of
which one, the median, is more developed than those which are situated
laterally. We denote these teeth, commencing with those nearest the
median line, by the names _central incisors_ or _nippers_,
_intermediate_ and _corner incisors_. The canines, or _fangs_, are long
and conical; they are curved backwards and outwards. The upper canines,
which are larger than those of the lower jaw, are separated from the
most external of the incisors (_corner_) by an interval in which the
canines of the lower jaw are received. The lower canines, on the other
hand, are in contact with the neighbouring incisors, and are each
separated from the first molar which succeeds them by a wider interval
than that which is situated between the corresponding teeth in the upper
jaw.

The molars differ essentially from the teeth of the same class in the
human species. Their crown terminates in a cutting border bristling with
sharp-pointed projections; this formation indicates that these teeth are
principally designed for tearing. During the movement of raising the
lower jaw, which is so energetic in the carnivora, they act, indeed, in
the same manner as the two blades of a pair of scissors. The largest
molars are: in the dog, the fourth of the upper jaw, and the fifth in
the opposite one; in the cat, the third both above and below.

The pig has forty-four teeth disposed in the following manner:

  7_m._  1_c._  3_i._ | 3_i._  1_c._  7_m._
  --------------------+-------------------- = 44.
  7_m._  1_c._  3_i._ | 3_i._  1_c._  7_m._

Of the incisors, the nippers and the intermediate ones of the upper jaw
have their analogues in those of the horse; in the lower jaw, the
corresponding teeth, straight, and directed forward, rather resemble the
same incisors in rodents. The corner incisor teeth are much smaller, and
are separated from the neighbouring teeth. The canine teeth, also called
_tusks_ or _tushes_, are greatly developed, especially in the male. The
molars increase in size from the first to the last; they are not
cutting, as in the carnivora, but they are not flattened and provided
with tubercles on their surfaces of contact as in the herbivora.

In the ox and the sheep the teeth are thirty-two in number:

  6_m._  0_c._  0_i._ | 0_i._  0_c._  6_m._
  --------------------+-------------------- = 32.
  6_m._  0_c._  4_i._ | 4_i._  0_c._  6_m._

As we see from this dental formula, the incisors are found only in the
lower jaw; they are replaced in the upper jaw by a thick cartilaginous
pad on which the inferior incisors find a surface of resistance.

These have their crowns flattened from above downwards, and gradually
become thinner from the root to the anterior border, which is edged and
slightly convex. These teeth gradually wear away. In proportion to the
progress of this wear, on account of the fact that it involves the
anterior borders and upper surfaces of the incisor teeth, and that these
teeth are narrower towards the root than at the opposite extremity, the
intervals which separate them tend to become wider and wider; and when
the roots become exposed by the retraction of the gums, they are then
separated from one another by a considerable interval. The molars have
their grinding surface comparable to that of the horse; they increase in
size from the first to the sixth.

The teeth of the horse are forty in number; they are thus distributed:

  6_m._  1_c._  3_i._ | 3_i._  1_c._  6_m._
  --------------------+-------------------- = 40.
  6_m._  1_c._  3_i._ | 3_i._  1_c._  6_m._

As they become worn, these teeth continue to grow, and as, on the one
hand, this phenomenon takes place throughout the whole life of the
animal, and, on the other hand, the process of wear brings out and makes
visible at the surface of friction parts formerly deeper and deeper, and
of which the configuration varies at different levels, there result
special features which permit the determination of the age of the animal
by an examination of its jaws. The incisors are called, commencing with
those situated nearest the middle line, _central incisors_ or _nippers_,
_intermediate_ and _corner incisors_. The canines, also designated as
the _fangs_, exist only in the male. It is exceptional to find them in
the mare, and when they exist in this latter they are less developed
than those of the horse. The molars have cuboid crowns; the surface of
friction is almost square in the case of the upper molars, and is
inclined so as to look inwards; in the case of the inferior ones, it is
a little narrowed, and is inclined so as to look outwards. In the upper
jaw the external surface of the crown is hollowed by two longitudinal
furrows; in the lower jaw the same surface has only one furrow, which at
times is but slightly marked.

In the hare the teeth are twenty-eight in number:

  6_m._  0_c._  2_i._ | 2_i._  0_c._  6_m._
  --------------------+-------------------- = 28.
  5_m._  0_c._  1_i._ | 1_i._  0_c._  5_m._

The four incisors of the upper jaw are divided into two groups; one of
these is formed by the two principal teeth, the other by two very small
incisors which are placed behind the preceding.

Having studied the jaws and examined the arrangement of the teeth, we
should say a few words on the movements which the lower jaw is able to
execute. In man, these movements are varied in character: the jaw is
lowered and raised; it can also be projected forwards and drawn
backwards, or carried to the right or left side by lateral movements.
Owing to the different modes of nutrition of animals, with which the
shape of the teeth is clearly correlated, being more specialized than in
the human species, the lower jaw is moved in a fashion less varied and
in the direction most suitable for the mastication of the foods which
form the aliment of the species considered. Moreover, this is plainly
shown in the skeleton by the shape of the condyle of the lower jaw (see
p. 122, different forms of this condyle). In the carnivora, whose teeth,
as we have seen, are all cutting ones, the jaw rises and falls; the food
then is, if we consider the two jaws, cut as by the blades of a pair of
scissors. In the ruminants, the incisors exist only in the lower jaw,
but the molars are thick and well developed; the food is ground by these
latter as by millstones, and the movements which favour this action are,
above all, the lateral. As for the rodents, in which the incisors are
formed for filing down and cutting through hard resisting bodies, their
lower jaw moves in the antero-posterior direction, in such a way that
the inferior incisors alternately advance and recede beneath those of
the upper jaw. The free cutting border of these teeth effectively
fulfils the function to which they are destined; their constant wear
preserves and revivifies the chisel edge which characterizes them,
without leading to their destruction, for the incisors in rodents are of
continuous growth.


THE SKULL OF BIRDS

=The Skull of Birds= (Fig. 65).--If, because it is less important from
the artistic point of view, we do not consider it necessary to describe
in detail the skull of birds, we yet think it useful to indicate, in
their general lines, the peculiarities it presents.

In this group the skull is generally pear-shaped; to the cranium, of
which the bones are arranged in such a way as to give it a form more or
less spherical, succeeds a face more or less elongated, according as the
bill is more or less developed.

In general, the bones of the skull coalesce very early, with the result
that it is only in very young individuals that we can determine their
presence.

We find the skull to consist of an occipital bone, two parietals, a
frontal, etc.; we will indicate but one detail in connection with these
bones: it is the presence of a single condyle for the articulation of
the occipital bone with the atlas. We also note the quadrate bone, which
is situated on the lateral part of the cranium, is movable on this
latter, and acts as an intermediary between it, the bones of the face,
and the lower jaw. The quadrate bone is regarded as a detached portion
of the temporal; on the signification of this we do not now propose to
dwell.

[Illustration: FIG. 65.--SKULL OF THE COCK: LEFT LATERAL SURFACE.

1, Occipital bone; 2, parietal bone; 3, frontal bone; 4, ethmoid bone;
5, cavity of the tympanum; 6, quadrate bone; 7, superior maxillary bone;
8, malar bone; 9, nasal bone; 10, 10, intermaxillary bone; 11, nasal
orifice; 12, os unguis or lachrymal bone; 13, inferior maxillary bone.]

On the anterior portion of the face we find the nasal bones, which,
articulating with the frontal on one side, circumscribe, on the other,
the posterior border of the nares. The nasal bone of the one side is
separated from that of the opposite by the intermaxillary or
premaxillary bone, which forms the skeleton of the superior mandible.

The superior maxillaries, which are rudimentary, are situated on the
lateral parts, and prolonged backward by an osseous style which
articulates with the quadrate bone; this styloid bone, the homologue of
the malar, is designated by certain authors as the _jugal_ or
_quadrato-jugal_ bone.

It is with the quadrate bone also that the inferior maxillary
articulates.




CHAPTER II

MYOLOGY


The first point to decide in commencing this study is the order in which
we shall consider the different muscles which we have to examine. It
must not be forgotten that in the present work we compare the
organization of animals with that of man, which we already know, and
that it is on the construction of this latter that, in these studies,
the thought must at each instant be carried back in order to establish
this comparison. Now, the general tendency which we notice in our
teaching of anatomy, when one regards the region of the trunk in the
human figure (a living model or a figure in the round), is first to
consider the anterior aspect. It is the latter that, for this reason, we
study at the very beginning; we next deal with the posterior surface of
the trunk, because it is opposite; lastly, the lateral surfaces, because
they unite with the preceding surfaces, the one to the other.

In studying an animal, it is usually by one of its lateral aspects that
one first observes it; it is, in fact, by these aspects that it presents
its greatest dimensions, and that the morphological characters as a
whole can be more readily appreciated. Hence, possibly, the order of
description adopted in most texts, or in the figures which accompany
them. The first representation of the human figure as a whole, in a
treatise on anatomy, represents the anterior aspect; the first view of
the horse as a whole, in a treatise on veterinary anatomy, for example,
is, on the other hand, a lateral view.

We break with this latter custom, and, without taking into account the
tendency above indicated, we will commence our analysis with the study
of the aspect of the trunk, which corresponds to the anterior aspect of
the same region in man.

The first muscles usually presented for study to artists being the
pectorals, it is their homologues that we will first describe here. We
will afterwards describe the abdominal region, then the muscles which
occupy the dorsal aspect of the trunk. With regard to the lateral
surfaces, they will be found, by this fact alone, almost completely
studied, since the muscles of the two preceding (back and abdomen),
spreading out, so to speak, over them, contribute to their formation.
Nothing further will remain but to incorporate with them the muscles of
the shoulder; but these will be studied in connection with the anterior
limbs, from which they cannot be separated.

The neck, in man, may be considered in an isolated fashion, because, on
account of its narrowness in proportion to the width of the shoulders,
it is clearly differentiated from the trunk; for this reason we combine
the study of it with that of the head. In animals, because of the
absence or slight development of the clavicles, the neck is generally
too much confounded with the region of the shoulders to make it
legitimate to separate it from that region in too marked a fashion. It
will, accordingly, be considered next.

We will then undertake the study of the muscles of the limbs, and end
with the myology of the head.


THE MUSCLES OF THE TRUNK

We shall divide them into muscles of the thorax, of the abdomen, and of
the back.


Muscles of the Thorax

=The Pectoralis Major= (Fig. 66, 1, 2; Fig. 67, 3, 4; Fig. 68, 7; Fig.
69, 10; Fig. 70, 11).--Further designated by the name of _superficial
pectoral_, this muscle is described in treatises on veterinary anatomy
as formed of two portions: an anterior one, called the _sterno-humeral_
muscle; the other, situated below and behind the preceding, bearing the
name of _sterno-aponeurotic_.

It occupies the region of the breast, and, as a whole, it takes origin
from the median portion of the sternum, from which it is directed
towards the arm and forearm.

The anterior portion (sterno-humeral muscle)--thick, forming an
elevation under the skin, and really constituting the pectoral
region--is directed downwards and outwards to be inserted into the
anterior margin of the humerus--that is to say, to the ridge which
limits in front the spiral groove of this bone.

The other part (sterno-aponeurotic muscle) is situated more posteriorly,
and corresponds to the region known in veterinary anatomy as the
_inter-fore-limb space_, which is limited laterally on each side by the
superior portion of the forearm, of which the point of junction with the
trunk bears the name _ars_. Arising from the sternum, as we have above
indicated, this portion is directed outwards, to be joined with the
terminal aponeurosis of the sterno-humeral, and with that which covers
the internal surface of the forearm.

All things considered, the sterno-humeral muscle may be regarded as the
representative of the upper fibres of the great pectoral of man, of
which the attachments, owing to the more or less complete absence of the
clavicle in the domestic mammals, the fibres must be concentrated on
the sternum; the sterno-aponeurotic portion then representing the
inferior fasciculæ of the same muscle.

[Illustration: FIG. 66.--MYOLOGY OF THE HORSE: ANTERIOR ASPECT OF THE
TRUNK.

1, Pectoralis major (sterno-humeral); 2, pectoralis major
(sterno-aponeurotic); 3, mastoido-humeralis; 4, point of the shoulder;
5, sterno-mastoid or sterno-maxillary: 6, inferior portion of the
platysma myoides of the neck, divided; 7, triceps cubiti; 8, brachialis
anticus; 9, radialis (anterior extensor of the metacarpus); 10, scapular
region.]

The great pectoral muscle of one side is separated from that of the
opposite side along the median line, and especially above and in front,
by a groove which is more or less deep, according as the muscles are
more or less developed. At the bottom of this groove, suggestive of that
which exists in the corresponding region in man, is found, as in this
latter, the median portion of the sternum.

The preceding description particularly applies to the arrangement which
the great pectoral presents in the horse; in other animals it is marked
by some distinctive characters. In the pig, it is inserted into the
sternum as far only as the level of the third costal cartilage; in the
ox and sheep, it extends as far as the sixth; in the dog, it is
attached to the two first sternal pieces only--that is to say, as far as
the third costal cartilage. Moreover, in the latter, as in the cat, the
two portions which we have indicated are less readily distinguished.

The great pectoral, by its contraction, draws the fore-limb towards the
middle line--that is to say, adducts it.

=The Pectoralis Minor= (Fig. 67, 6; Fig. 68, 8; Fig. 69, 11; Fig. 70,
12, 26).--This muscle, also called the _deep pectoral_, is, in animals,
larger than the superficial pectoral, therefore certain authors prefer
to give to this muscle and the preceding one the names of deep and
superficial pectoral respectively. This nomenclature is evidently
legitimate, and conforms more to reality, since it does not bring in the
notion of dimensions which here is found in contradiction to
nomenclature; but, in order to establish more clearly the parallelism
with the corresponding muscles in man, we think it better, nevertheless,
to give them the names by which it has been customary to designate them
in connection with the latter.

We will recall at the outset that the lesser pectoral muscle in man is
completely covered by the great. In animals this is not the case; the
lesser pectoral being very highly developed, projects beyond the great
pectoral posteriorly, and occupies to a greater or less extent the
inferior surface of the abdomen.

It also consists of two parts: one anterior, which we designate by the
name of _sterno-prescapular_; the other, posterior, bearing that of
_sterno-humeral_.[20]

  [20] This division of the pectorals certainly complicates the
       nomenclature of these muscles; nevertheless, it introduces no
       insuperable difficulty from the mnemonic point of view. But where
       the study becomes less profitable, and comparison with the
       corresponding muscles in man more complicated, is in adopting the
       nomenclature of Bourgelat. Indeed, the great pectoral is
       designated by this author the 'common muscle of the arm and
       forearm,' while the lesser pectoral (or deep pectoral) is called
       the 'great pectoral' in its sterno-trochinian and 'lesser
       pectoral' in its sterno-prescapular portion. We do not consider
       it necessary to give the other theories relative to the
       homologies of these, notwithstanding the very real interest which
       they present from the purely anatomical point of view, as they
       have but few applications in the study of forms.

The sterno-prescapular muscle, being covered by the sterno-humeral, has
little interest for us. It arises from the sternum, and is directed
towards the angle formed by the junction of the scapula and humerus;
then it is reflected upwards and backwards, to terminate on the anterior
margin of the shoulder by insertion into the aponeurosis, which covers
the supraspinatus muscle.

We can, especially in the horse after removal of the skin, recognise it,
at the level of this region, in the interspace limited by the
superficial muscles (Fig. 70, 26).

In the dog and cat this portion of the muscle does not exist. The other
division of the muscle, the sterno-trochinian, is more interesting. It
arises from the abdominal aponeurosis and the posterior part of the
sternum; hence it passes forward, turns under the superficial pectoral,
and is inserted into the lesser tuberosity (trochin) of the humerus.

In the pig, dog, and cat, it is inserted into the greater tuberosity
(trochiter) of the bone of the arm.

The superior border of this muscle is in relation with a superficial
vein, which is distinctly visible in the horse--the subcutaneous
thoracic vein, which in this animal is called the vein of the spur.

The sterno-humeral muscle, in contracting, draws the shoulder and the
whole anterior limb backwards.

=Serratus Magnus= (Fig. 67, 2; Fig. 69, 8; Fig. 70, 9).--This muscle,
which is situated on the lateral aspect of the thorax, is covered to a
considerable extent by the shoulder, the posterior muscular mass of the
arm, and by the great dorsal muscle.

It arises by digitations from the external surface of the dorsal
vertebræ; from the first eight in the horse, ox, and dog.

[Illustration: FIG. 67.--MYOLOGY OF THE HORSE: INFERIOR ASPECT OF THE
TRUNK.

1, Anterior extremity of the sternum; 2, point of the shoulder and
inferior portion of the mastoido-humeral muscle; 3, pectoralis major
(sterno-humeral); 4, pectoralis major (sterno-aponeurotic); 5, point of
the elbow; 6, pectoralis minor (sterno-trochinian); 7, serratus magnus;
8, external oblique; 9, sheath of the rectus abdominis; 10, linea alba;
11, the umbilicus; 12, external oblique divided in order to expose the
rectus abdominis; 13, rectus abdominis.]

The muscular bundles, converging as they proceed, towards the scapula,
pass under this bone, to be inserted into the superior portion of the
subscapular fossa, near the spinal border. The inferior portion of its
posterior digitations is visible in the ox and in the horse; these
digitations are less visible in the pig. They are not seen at all in the
dog (Fig. 68) or cat, for in these animals the great dorsal muscle
covers them completely.

The great serratus muscle, by the position which it occupies and the
arrangement that it presents, forms with the corresponding muscle of the
opposite side a sort of girth, which supports the thorax, and at the
same time helps to fix the scapula against the latter.

When it contracts, in taking its fixed point at the ribs, it draws the
superior portion of the scapula downwards and backwards in such a way
that this bone has its inferior angle directed forwards and upwards. If
it takes its fixed point at the shoulder, it then acts on the ribs,
raises them, and so becomes a muscle of inspiration.

Because of the connections of the serratus magnus with the levator
anguli scapulæ, some authors consider it as united with the latter. But
as the latter muscle is visible only in the region of the neck (see p.
157), and as it is separately described in man, we prefer to distinguish
them from one another. We shall recall the connections to which we have
just made allusion when describing the cervical region.


Muscles of the Abdomen

The abdominal wall is, as in man, formed by four large muscles: the
external oblique, the internal oblique, and the transversalis, which
form the lateral walls, and the rectus abdominis, situated on each side
of the middle line of the abdomen. This latter, because of the general
direction of the trunk in quadrupeds, has its superficial surface
directed downwards.

The arrangement of these muscles closely corresponds to that which we
find in the human species.

=The External Oblique Muscle= (Fig. 67, 8, 12; Fig. 68, 5; Fig. 69, 9;
Fig. 70, 10).--This muscle arises, by digitations, from a number of
ribs, which varies according to the species, the number of the ribs
being itself variable for each of them, as we pointed out in connection
with the osteology of the thorax. Indeed, the great oblique arises from
the eight or nine posterior ribs in the dog and the ox, and from the
thirteen or fourteen posterior in the horse. It is attached, besides, to
the dorso-lumbar aponeurosis.

These attachments are arranged in a line directed obliquely upwards and
backwards, and the first digitations--that is to say, the most anterior
ones--dovetail with the posterior digitations of origin of the great
serratus muscle.

The fleshy fibres are directed downwards and backwards, and terminate in
an aponeurosis which covers the inferior aspect of the abdomen, and
proceeds to form the linea alba by joining with that of the muscle of
the opposite side, and also to be inserted into the crural arch.

This aponeurosis of the external oblique is covered by an expansion of
elastic fibrous tissue, which doubles it externally, and which is known
as the _abdominal tunic_. This latter is further developed as the organs
of the digestive apparatus are more voluminous, and their weight,
consequently, more considerable. For this reason, in the large
herbivora, as the ox and the horse, this tunic is extremely thick,
whereas in the pig, cat, and dog it is, on the contrary, reduced to a
simple membrane. Indeed, in these latter, the abdominal viscera being
less developed, the inferior wall of the abdomen does not require so
strong a fibrous apparatus for supporting them. The great oblique, when
it contracts, compresses the abdominal viscera in all circumstances
under which this compression is necessary; it also acts as a flexor of
the vertebral column.

=The Internal Oblique Muscle.=--This muscle, which is covered by the
preceding, arises from the anterior superior iliac spine (external angle
in ruminants and solipeds) and the neighbouring parts. From this origin
its muscular fibres, the general direction of which is opposite to that
of the fibres of the external oblique, diverging, proceed to terminate
in an aponeurosis, which contributes to the formation of the _linea
alba_, and to be attached superiorly to the internal surface of the last
costal cartilages. It has the same action as the great oblique. What it
presents of special interest is the detail of form which it determines
in the region of the flank; this detail is _the cord of the flank_. It
is characterized by an elongated prominence which, starting from the
iliac spine, is directed obliquely downwards and forwards, to terminate
near the cartilaginous border of the false ribs.

Often very apparent in the ox, and still more so in the cow, the cord in
question contrasts with the depression which surmounts it; this
depression is situated below the costiform processes of the lumbar
vertebræ, and is called the _hollow of the flank_. It is so much the
more marked as the mass of the intestinal viscera is of greater weight.

We sometimes meet with a case of the presence of this hollow in the
horse. But when in the latter, the flank is well formed, the hollow is
scarcely visible, and the cord but slightly prominent. It is only in
emaciated subjects that these details are found clearly marked.

=Transversalis Abdominis.=--This muscle being deeply situated does not
present any interest for us. We will, however, point out, in order to
complete the series of muscles which form the abdominal wall, that the
direction of its fibres is transverse, and that they extend from the
internal surface of the cartilages of the false ribs, and the costiform
processes of the lumbar vertebræ to the _linea alba_.

=The Rectus Abdominis= (Fig. 67, 13; Fig. 68, 6).--This muscle,
enclosed, as it is in man, in a fibrous sheath (Fig. 67, 9) formed by
the aponeuroses of the lateral muscles of the abdomen, is a long and
wide fleshy band, which, as in the human species, reaches from the
thorax to the pubis.

What distinguishes it in quadrupeds is that there are costal attachments
which extend further on the sternal surface of the thorax, and the
number of its aponeurotic insertions, which, in general, is more
considerable. These are, indeed, six or seven in number in the pig and
in ruminants, and about ten in the horse.

It is true that we may find but three in the cat and dog; still, we
often find as many as six. These intersections are not marked on their
exterior by transverse grooves, such as we find in the human species in
individuals with delicate skin and whose adipose tissue is not very much
developed.

The rectus abdominis is covered, in its anterior portion, by the
sterno-trochinian muscle (posterior segment of the small pectoral). In
contracting, this muscle brings the chest nearer the pelvis, and as a
result flexes the vertebral column. It also contributes to the
compression of the abdominal viscera.

=Pyramidalis Abdominis.=--This unimportant little muscle, which in man
is situated at the lower part of the abdomen, extends from the pubis to
the _linea alba_. It is not present in the domestic animals.

We consider it interesting, however, to point out, although the fact is
not a very useful one as regards external form, that this muscle is
distinctly developed in marsupials.

We know that in the opossum, the kangaroo, and the phalanger fox, the
young are brought forth in an entirely incomplete state of development,
and that, during a certain period, they are obliged to lodge in a pouch
which is placed at the lower part of the abdomen of the mother. Now,
this pouch contains the mammary glands; but the young, being too feeble
to exercise the requisite suction, the pyramidal muscles come to their
assistance. These muscles, in contracting, approximate to one another
two bones which are placed above the pubis, the (so-called) marsupial
bones (see Fig. 80); by their approximation the bones in question, which
are placed behind and on the outer side of the mammary glands, compress
the latter, and thus is brought about the result which the little ones,
on account of their feebleness, would, without that intervention, be
incapable of obtaining for themselves.


Muscles of the Back

=Trapezius= (Fig. 68, 1, 2; Fig. 69, 1, 2; Fig. 70, 1, 2).--This muscle,
more or less well developed, according to the species, is divided into
two portions, of which the names indicate the respective situations--a
cervical and a dorsal.

These two parts, considered in the order in which we find them, take
their origin from the superior cervical ligament and from the spinous
processes of the first dorsal vertebræ. From these different points the
fibres are directed towards the shoulder; the anterior are,
consequently, oblique downwards and backwards, and the posterior are
directed downwards and forwards. They are inserted into the scapula in
the following manner: the fibres of the dorsal portion are attached to
the tuberosity of the spine; those of the cervical region are also fixed
into the same spine, but into a considerably larger surface.

The cervical portion occupies, in the region of the neck, an area
relatively smaller than the corresponding portion of the trapezius in
man. This diminished degree of development results from the absence,
complete, or nearly so, of the clavicle in the animals which we are now
considering. We remember, that the trapezius of man is partly inserted
into the clavicle, and the disappearance of this latter cannot fail to
bring modifications in the general disposition of the corresponding
portion of the muscle. There results a disconnection of this latter, and
it becomes united to other muscular fibres to form a muscle with which
we shall soon have to deal--the mastoido-humeral (see p. 150).

As specific differences we should add that the trapezius occupies a more
or less extensive portion of the median and superior regions of the
neck; terminating at a considerable distance from the head in the dog
and horse, it, on the contrary, approaches it in the pig and in
ruminants. The cervical portion, when it contracts, draws the scapula
upwards and forwards, the dorsal portion draws it upwards and backwards.
When the trapezius acts as a whole the scapula is raised.

[Illustration: FIG. 68.--MYOLOGY OF THE DOG: SUPERFICIAL LAYER OF
MUSCLES.

1, Trapezius, cervical portion; 2, trapezius, dorsal portion; 3,
superior outline of the scapula; 4, latissimus dorsi; 5, external
oblique muscle; 6, rectus abdominis; 7, pectoralis major of the right
side; 8, pectoralis minor (sterno-trochinian); 9, 9, mastoido humeral
muscle; 10, tendinous intersection, at the level of which is found a
rudimentary clavicle; 11, sterno-mastoid muscle; 12, infrahyoid muscles;
13, omo-tracheal or acromio-tracheal muscle; 14, splenius; 15, levator
anguli scapulæ; 16, deltoid muscle, spinal portion; 17, deltoid,
acromial portion; 18, superior extremity of the humerus; 19,
supraspinatus; 20, infraspinatus; 21, biceps cubiti; 22, brachialis
anticus; 23, triceps cubiti, long head; 24, triceps cubiti, external
head; 25, olecranon process; 26, radialis (anterior extensor of the
metacarpus); 27, iliac crest; 28, gluteus maximus; 29, gluteus medius;
30, biceps cruris; 31, semitendinosus; 32, semi-membranosus; 33,
gastrocnemius; 34, tensor of the fascia lata; 35, sartorius; 36, fascia
lata drawn up by the triceps; 37, the patella or knee-cap; 38,
ischio-coccygeal muscle; 39, superior sacro-coccygeal; 40, lateral
sacro-coccygeal; 41, inferior sacro-coccygeal.]

=The Latissimus Dorsi= (Fig. 68, 4; Fig. 69, 5; Fig. 70, 5).--This
muscle arises by an aponeurosis, the so-called dorso-lumbar aponeurosis,
from the spinous processes of the last dorsal vertebræ (the seven last
in the dog, fourteen or fifteen last in the horse), from the spinous
processes of the lumbar vertebræ, and from the last ribs. Its fleshy
fibres are directed downwards and forwards, being more oblique in
direction posteriorly, and pass on the inner side of the posterior
muscular mass of the arm, to be inserted into the internal lip of the
bicipital groove of the humerus, or, a little lower down, on the median
portion of the internal surface of the same bone. This latter mode of
insertion is met with in the horse and the ox.

The anterior fibres cover the posterior angle of the scapula (as in man,
where the corresponding angle, but in this case inferior, is covered by
the same muscle), and, a little higher up, are in their turn concealed
by a portion of the dorsal fibres of the trapezius. It covers, to a
greater or less extent, the great serratus muscle. These relations are
similar to those found in the human species.

We find that the fleshy fibres of the great dorsal are prolonged more or
less backwards if we examine this muscle in the dog, the ox, the pig,
and the horse. Indeed, the fibres reach to the thirteenth rib in the dog
and the cat (that is to say, the last rib), the eleventh in the ox,
tenth in the pig, and twelfth only in the horse. We say 'only' in
connection with this last because it is necessary to remember that the
ribs are eighteen in number on each side of the thorax of this animal,
and that, accordingly, the fleshy fibres of the great dorsal muscle are,
relatively, of small extent.

When this muscle contracts it flexes the humerus upon the scapula, and
helps to draw the whole of the anterior limb backwards and upwards.

There is a muscular fasciculus which, because of its relations with the
muscle we have just been studying, is known as the _supplementary muscle
of the latissimus dorsi_. But as, on the other hand, this fasciculus is
in relation with the triceps, we shall in preference consider it in
relation with this latter (see p. 173).

[Illustration: FIG. 69.--MYOLOGY OF THE OX: SUPERFICIAL LAYER OF
MUSCLES.

1, Trapezius, cervical portion; 2, trapezius, dorsal portion; 3, outline
of the scapula; 4, spine of the scapula; 5, latissimus dorsi; 6, small
posterior serratus; 7, prominence caused by the costiform processes of
the lumbar vertebræ; 8, serratus magnus; 9, external oblique; 10,
pectoralis major (sterno-humeral); 11, mastoido-humeralis; 12, atlas;
13, atlas; 14, parotid gland; 15, sterno-mastoid muscle; 16, infrahyoid
muscles; 17, omo-trachelian or acromio-trachelian muscle; 18, deltoid;
19, brachialis anticus; 20, triceps, long head; 21, triceps, external
head; 22, olecranon; 23, radialis (anterior extensor of the metacarpus);
24, anterior iliac spine; 25, gluteus maximus; 26, gluteus medius; 27,
biceps cruris; 28, semitendinosus; 29, gastrocnemius; 30, tensor of the
fascia lata; 31, fascia lata covering the triceps of the thigh; 32,
patella; 33, ischio-coccygeal muscle; 34, superior ischio-coccygeal; 35,
lateral ischio-coccygeal; 36, inferior ischio-coccygeal.]

The aponeurosis by which the great dorsal arises from the vertebral
column covers, as in man, the muscles which occupy the grooves situated
on each side of the spinous processes--the spinal muscles or common
muscular mass, if we regard them as a whole (Fig. 70, 7); the
sacro-lumbar and the long dorsal muscles covering the transverse spinal,
if we consider them as distinct.

It would be superfluous to enter here into a detailed examination of
these muscles.

If they are but little developed the spinous processes become prominent
under the skin; if they are more so they may by their thickness project
beyond the level of these processes, and these latter thus come to lie
in a groove more or less marked, which, on account of the division which
is determined by its presence, has caused the regions which it occupies
to be designated by the names _double back_ and _double loins_.

The muscles are extensors of the vertebral column.

Under the aponeurosis of the great dorsal muscle there is found in man
another muscle, the serratus posticus inferior, which, on account of
being deeply placed and its slight thickness, offers nothing of interest
in connection with the study of external form. It arises from the
spinous processes of the three last dorsal vertebræ and those of the
three first lumbar; it then passes upwards and outwards, and divides
into four digitations, to be inserted into the inferior borders of the
four last ribs. We repeat that it is covered by the great dorsal muscle.

In the pig, ox, and horse, which have this latter muscle less developed
in its posterior portion, the same small serratus muscle, known as the
_posterior serratus_, is visible in the superficial layer of muscles
(Fig. 69, 6; Fig. 70, 6). The number of its digitations is more or less
considerable according to the species examined.

=The Rhomboid Muscle= (Fig. 70, 21).--In order to make intelligible the
position of the rhomboid in the superficial layer in quadrupeds, it
appears to us necessary to recall the anatomical characters of the
muscle as found in man. The rhomboid arises from the inferior portion of
the posterior cervical ligament, from the spinous process of the seventh
cervical vertebræ and the four or five upper dorsal; thence passing
obliquely downwards and outwards, it is inserted into the spinal border
of the scapula, into the portion of this border which is situated below
the spine; it sometimes extends to the middle of the interval which
separates this latter from the superior internal angle of the same bone.

The portion of the muscle which arises from the cervical ligament and
the seventh cervical vertebra is often separated from the lower portion
by a cellular interspace. For this cause some anatomists have described
the rhomboid as consisting of two parts--the superior or small rhomboid
and the inferior or large rhomboid, on account of the position occupied
by each, and of their difference in volume.

This muscle can only be seen in the region of the back, in the space
limited externally by the spinal border of the scapula, below by the
latissimus dorsi, and internally by the trapezius, which covers it in
the rest of its extent. It is not in this space that it is seen in
certain quadrupeds. As we pointed out in the section on osteology, the
spinal border of the scapula is short, and it seems to be due to this
limitation in length that the trapezius and the latissimus dorsi muscle
are, at this level, in contact the one with the other in such a way that
they fill up the interval in which the rhomboid is seen in man.

In the horse we can partly see it in the superficial muscular layer, but
in the region of the neck only, at the superior border of the shoulder.
Indeed, as we have already pointed out, the trapezius does not reach the
occipital protuberance; for this reason a part of the anterior portion
of the rhomboid may be seen--that is, the portion which corresponds to
the superior part of the human muscle.

But whether it be covered by the trapezius, or, as we find in the cat
and dog, by the _mastoido-humeral muscle_ (see p. 150), which is very
broad in this region, we do not the less recognise its presence; and in
the horse and ox, in particular, it forms an elongated prominence
beginning at the level of the scapula, and tapering as it ascends,
towards the posterior part of the head.

[Illustration: FIG. 70.--MYOLOGY OF THE HORSE: SUPERFICIAL LAYER OF
MUSCLES.

1, Trapezius, cervical portion; 2, trapezius, dorsal portion; 3,
superior outline of the scapula; 4, spine of the scapula; 5,
latissimus dorsi muscle; 6, small posterior serratus; 7, spinal muscles,
or common muscular mass; 8, ribs; 9, serratus magnus; 10, external
oblique; 11, pectoralis major (sterno-humeral); 12, pectoralis
minor (sterno-trochinian); 13, atlas; 14, parotid gland; 15,
mastoido-humeralis; 16, point of the arm; 17, sterno-mastoid, or
sterno-maxillary; 18, jugular groove; 19, infrahyoid muscles; 20,
omo-trachelian muscle; 21, rhomboid; 22, splenius; 23, levator anguli
scapulæ; 24, deltoid; 25, supraspinatus; 26, terminal part of the
sterno-prescapular, a portion of the small pectoral muscle; 27,
brachialis anticus; 28, triceps cubiti, middle or long head; 29, triceps
cubiti, external head; 30, olecranon; 31, radial extensor (anterior
extensor of the metacarpus); 32, anterior iliac spine; 33, anterior
portion of the gluteus maximus--the aponeurosis of the muscle has been
divided in order to expose the gluteus medius; 34, posterior portion of
the gluteus maximus; 35, gluteus medius; 36, biceps cruris; 37,
semitendinosus; 38, point of the buttock; 39, gastrocnemius; 40, tensor
of the fascia lata; 41, triceps cruris; 42, ischio-coccygeal muscle; 43,
superior sacro-coccygeal; 44, lateral sacro-coccygeal; 45, inferior
sacro-coccygeal.]

Its origins are similar to those which we have already described in the
human rhomboid. It arises from the cervical ligament and the spinous
processes of the foremost dorsal vertebræ; its fibres converge and pass
to the scapula, to be inserted into its superior or spinal border, or
into the internal surface of the cartilage of prolongation.

It assists in keeping the scapula applied to the thoracic cage, and when
it contracts, draws the scapula upwards and forwards.

Taking its fixed point at the scapula, it acts on the neck by its
anterior fibres, and extends it.

We shall soon have occasion to mention this muscle again, in connection
with the study of the muscles of the neck.

=The Cutaneous Muscle of the Trunk= (Fig. 71).--Immediately beneath the
skin which covers the neck, shoulders, and trunk is found a vast
cutaneous muscle, analogous to that which, in the human species, exists
only in the cervical region.

This thin muscle, whose function is to move the skin which strongly
adheres to it, and in this way to remove from it material causes of
irritation (insects, for example), is of considerable thickness in the
region of the trunk; where it constitutes what certain authors have
designated by the name of _panniculus carnosus_. In this region it
extends from the posterior border of the shoulder to the thigh, and, in
the vertical direction, from the apices of the spinous process of the
dorso-lumbar vertebræ to the median line of the abdomen.

Arising above from the supraspinous ligament of the dorso-lumbar and
sacral regions (except in the carnivora; see below) by an aponeurosis
which, posteriorly, covers the muscles of the hind-limbs, its fibres are
directed to the elbow, on which they are arranged in two layers: a
superficial, which becomes continuous with the panniculus muscle of the
shoulder; and a deep, which passes on the inner side of the shoulder to
be inserted into the internal surface of the humerus; this latter exists
only in the dog and cat.

The most inferior fibres, behind, at the level of the knee-cap form a
triangular process which in the horse receives the name of the _stifle
fold_, from the name veterinarians give to the region of the
articulation of the knee. This fold of skin, which commences on the
antero-internal surface of this region, is directed upwards, and then
forwards, to end by gradually disappearing over the corresponding part
of the abdomen.

[Illustration: FIG. 71.--MYOLOGY OF THE HORSE: PANNICULUS MUSCLE OF THE
TRUNK.]

In the same animal the muscular fibres of the panniculus of the trunk
arise along a line which connects the stifle-joint to the withers, a
line which is, consequently, oblique upwards and forwards. Now, as the
fleshy layer is thicker than the aponeurosis, the result is that the
mode of constitution of this muscle can be recognised under the skin.
Indeed, we can see in some animals, occasionally very distinctly, a
slight elevation starting from the region of the abdomen in the
neighbourhood of the knee, and thence directed obliquely upwards and
forwards. This elevation is produced by the fleshy portion of the
panniculus.

In the carnivora, the panniculus of the trunk is not attached to the
supraspinous ligament; it is blended with the same muscle of the
opposite side, passing over the spinous region of the vertebral column.

From this arrangement results a great mobility of the skin which covers
the back. Further, it explains why it is possible to lift up this skin
along with the panniculus which it covers, and to which it adheres,
throughout the whole extent of the dorso-lumbar column. As we pointed
out above, there is also a panniculus muscle of the shoulder and one of
the neck. We will deal with them when treating of the regions to which
those muscles belong.


The Coccygeal Region

As a sequel to the study of the muscles of the region of the trunk very
naturally comes the description of those which, belonging to the region
of the coccyx, are destined for the movements of the caudal appendix, of
which this latter constitutes the skeleton. The muscles may not seem to
be of much importance with regard to external form, but, as they form
part of the superficial muscular layer, and as the mass of each is
seen in the form of the tail in some animals (the lion, for example),
they merit our attention for a moment. A few lines will suffice to
give an idea of them. They are: the _ischio-coccygeal_, _superior
sacro-coccygeal_, _lateral sacro-coccygeal_, and _inferior
sacro-coccygeal_.

=The Ischio-coccygeal= (Fig. 18, 38; Fig. 69, 33; Fig. 70, 42).--This
muscle, triangular in shape, better developed in the carnivora than in
the horse, arises from the spine of the ischium, or from the
supracotyloid crest, which replaces this latter in the solipeds and the
ruminants. Thence its fleshy mass is directed upwards, expanding as it
proceeds to be inserted into the transverse processes of the first two
coccygeal vertebræ after insinuating itself between two of the following
muscles, the lateral and inferior sacro-coccygeal.

In the dog and cat, the muscle is in great part covered by the great
gluteal. In the ox, by a peculiar arrangement of the corresponding
region of the muscles of the thigh--an arrangement which we will examine
in connection with the study of the latter--it is more exposed than in
the horse, and gives origin to an outline which corresponds to its
general form in the region situated immediately below the root of the
tail.

It is a depressor of the whole caudal appendix.

=The Superior Sacro-coccygeal= (Fig. 68, 39; Fig. 69, 34; Fig. 70,
43).--The fasciculi which form this muscle arise from the crest of the
sacrum, and proceed thence to end successively on the coccygeal
vertebræ. It is in contact in the middle line with the corresponding
muscle of the opposite side.

It raises the tail and inclines it laterally; if the muscle of one side
contracts at the same time as that of the other the tail is elevated
directly.

=The Lateral Sacro-coccygeal= (Fig. 68, 40; Fig. 69, 35; Fig. 70,
44).--Situated on the lateral part of the caudal region, this muscle
arises, in the dog, from the internal border of the iliac bone and the
external border of the sacrum; in the horse, it arises from the crest of
the sacrum. It is inserted into the coccygeal vertebræ.

It produces lateral movement of the tail.

=The Inferior Sacro-coccygeal= (Fig. 68, 41; Fig. 69, 36; Fig. 70,
43).--This muscle, which is fairly thick, arises from the inferior
surface of the sacrum and the corresponding surface of the sacro-sciatic
ligament; it is inserted into the coccygeal vertebræ.

It depresses the caudal appendix.


Muscles of the Neck

=Mastoido-humeralis= (Fig. 66, 3; Fig. 68, 9, 9, 10; Fig. 69, 12; Fig.
70, 15).--One of the most important muscles of the region of the neck in
man is the sterno-cleido mastoid. We recollect that, in its inferior
part, it is divided into two bundles, one of which arises from the
manubrium of the sternum, and the other from the inner third of the
clavicle, whence the denominations of the _sternal_ portion and
_clavicular_ portion. The muscle formed by the union of these two
portions is then directed obliquely outwards, backwards, and upwards, to
be inserted into the mastoid process of the temporal bone and the two
external thirds of the superior curved line of the occipital bone.

Now, the animals which we are here considering have but a rudimentary
clavicle or are entirely without it. From the absence of this item of
the skeleton there necessarily result modifications in the arrangement
of the muscles of this region, which we must at the very outset explain,
before undertaking the special study of the muscle which is the subject
of the present paragraph.

Let us suppose, for the more definite arrangement of our ideas, that the
clavicle is altogether absent, although we do find it in a rudimentary
state in some animals and completely developed in others (marmot, bat),
and we will proceed to indicate what this absence determines.

The great pectoral muscle in man arises in part from the clavicle; this
origin not being possible in animals which have no clavicle, its
attachments, as we have already seen, are concentrated on the sternum.
The trapezius in man similarly arises in part from the clavicle; for the
reasons above indicated its clavicular fasciculi cannot exist in
distinct form in the animals which have no clavicle.

The sterno-cleido mastoid, whose inferior attachments we mentioned
above, cannot have a clavicular portion.

It is the same in the case of the deltoid, which, we know, arises in
part from the anterior bone of the shoulder.

Of the four muscles which have partial clavicular origins in man, two
are known to us in connection with animals--the great pectoral and the
trapezius. What has become of the other two, the sterno-cleido mastoid
and the deltoid?

It is this which we now proceed to investigate. After a fashion
simple enough, but which it is necessary to describe, the clavicular
fasciculi of the trapezius and the corresponding fasciculi of the
sterno-cleido mastoid are united the one to the other; the portion
of the deltoid which in man arises from the clavicle, by reason of the
absence of this latter, is also combined with the fleshy mass formed by
the preceding muscles. From this fusion results the muscle known as the
mastoido-humeral. This muscle, which consists of a long fleshy band
situated on the lateral aspect of the neck, takes its origin, as a
general rule, from the posterior surface of the skull and the upper part
of the neck, from which it passes obliquely downwards and backwards,
covering the scapulo-humeral angle--that is, the region known as the
point of the shoulder or arm--and is inserted into the anterior border
of the humerus, the border which, limiting anteriorly the musculo-spiral
groove, forms a continuation of the deltoid impression. On account of
the regions with which it is related, Bourgelat named this muscle _the
muscle common to the head, neck, and arm_.

It is at the level of the scapulo-humeral angle that the vestiges of the
clavicle are found.

This bone is represented in some animals--the pig, ox, and horse--by a
single tendinous intersection, more or less apparent, which extends
transversely from the scapula to the anterior extremity of the sternum.
In the dog and the cat, we find, besides, on the deep surface of the
muscle and at the level of this tendinous intersection, the rudiment of
the clavicle of which we made mention in the section on Osteology (see
p. 25).

It is beneath the intersection, the existence of which we have just
pointed out, that is found that portion of the mastoido-humeral muscle
which corresponds to the clavicular fasciculi of the deltoid; that
portion which is situated above the intersection corresponds to the
clavicular fibres of the sterno-cleido-mastoid and of the trapezius.

The mastoido-humeral presents certain varieties in different animals.

In the dog and the cat, this muscle, which is blended above with the
sterno-mastoid (see p. 153), to be inserted with it into the mastoid
process and the mastoid crest, covers the neck for a considerable extent
from the superior curved line of the occipital bone to which it is
attached, to the trapezius with which it unites posteriorly, but from
which it separates below. Between these two extreme points of its
superior portion it is attached to the cervical ligament.

In the pig and in ruminants, in which the trapezius approaches more
closely to the head, the mastoido-humeral occupies, in consequence, a
less extent of the cervical region.

In the horse, the mastoido-humeral neither covers the neck nor joins the
trapezius; indeed, we have already shown that it is separated by a
considerable distance from the head. In the limited interval between
these two muscles a part of the rhomboid and parts of other muscles are
seen with which we shall soon be occupied.

This muscle, as regards the horse, is described by some anatomists as
consisting of two parts: one anterior, or superficial; the other
posterior, or deep. In reality, the first only corresponds to the
mastoido-humeral, which we are considering; the posterior may be more
exactly regarded as representing a special muscle of quadrupeds, but
which is here a little deformed, the _omo-trachelian_ (see p. 155).

When the mastoido-humeral contracts, taking its fixed point above, it
acts as an extensor of the humerus, and carries the entire fore-limb
forwards. If it takes its fixed point below--that is to say, at the
humerus--it inclines the head and neck to its own side. If it contracts
at the same time as the mastoido-humeral of the opposite side, then the
head and the neck are carried into the position of extension.

=The Sterno-mastoid= (Fig. 66, 5; Fig. 68, 11; Fig. 69, 15;
Fig. 70, 17).--Having described the clavicular portion of the
sterno-cleido-mastoid in connection with the mastoido-humeral, because
it forms a part of the latter, we have, in order to complete the
homologies of this muscle, to study now that which corresponds to its
sternal portion. This is the _sterno-mastoid_ muscle. In all the
quadrupeds with which we are here concerned this muscle arises from the
anterior extremity of the sternum; narrow and elongated in form, it
passes towards the head in a direction parallel to the anterior border
of the mastoido-humeral, from which it is separated by an interspace
which, along its whole length, lodges superficially the jugular vein;
hence the name of _jugular groove_, which is given to this part of the
neck (Fig. 10, 18).

It is inserted, in the case of the dog and cat, into the mastoid
process, where it is united with the mastoido-humeral; in the ox it is
divided into two portions--one which goes to the base of the occipital
bone, the other passing in front of the masseter is by the medium of
the aponeurosis of this latter attached to the zygomatic crest. This
latter part is considered by some writers as forming a portion of the
panniculus muscle of the neck.

In the horse it is attached to the angle of the lower jaw by a tendon,
which an aponeurosis that passes under the parotid gland binds to the
mastoido-humeral muscle and the mastoid process.

By reason of this insertion into the jaw, in the case of the solipeds,
this muscle is further named the _sterno-maxillary_.

When it contracts, it flexes the head, and inclines it laterally. This
movement is changed to direct flexion when the two sterno-mastoid
muscles contract simultaneously.

In man, the sterno-cleido-mastoid and the trapezius leave a triangular
space between them, which, being limited inferiorly by the middle third
of the clavicle, is known as the supraclavicular region; this region,
being depressed, especially in its inferior part, has also been given
the name of supraclavicular fossa--popularly called the '_salt-cellar_.'

The muscles which form the floor of this region, passing from above
downwards, are: a very small portion of the complexus, splenius, levator
anguli scapulæ, posterior scalenus, and anterior scalenus; then,
crossing these latter, and most superficial, is the omo-hyoid muscle.

An analogous region, but of only slight depth, exists in quadrupeds; its
borders are formed by the mastoido-humeral and trapezius muscles.

It is not limited below by the clavicle--we know, indeed, that this, or
the intersection which represents it, belongs to the mastoido-humeral
muscle--but by the inferior portion of the spine of the scapula.

It is of greater or less extent according to the species considered.

In the dog, cat, pig, and ox, it is narrow, for the muscles which bound
it approach one another pretty closely. It has, as in man, the form of a
triangle, with the apex above. In the horse it is much broader, and,
contrary to the arrangement which it presents in the human species, the
widest part is directed upwards.

The muscles which we find there are, consequently, more or less
numerous. In the dog and cat they are: a portion of a muscle which we do
not normally meet with in man--the _omo-trachelian_--then in a
decreasing extent: supraspinatus, levator anguli scapulæ and splenius.

In the pig: the omo-trachelian, supraspinatus, and the terminal portion
of the sterno-prescapular--the anterior part of the lesser or deep
pectoral muscle.

In the ox: the omo-trachelian only.

But in the horse we find the omo-trachelian, the supraspinatus, and the
terminal extremity of the sterno-prescapular; then in a larger extent of
area the levator anguli scapulæ and the splenius; and, finally, the
anterior portion of the rhomboid.

Among the muscles which we have just enumerated are some that we have
already studied; these are the sterno-prescapular and the rhomboid. We
will examine the supraspinatus muscle in connection with the region of
the shoulder.

As to the scaleni muscles and the complexus, they are deeply situated,
whereas the omo-hyoid is visible in the anterior region of the neck
only.

There remain for us, accordingly, to examine, at the present juncture,
but the omo-trachelian, levator anguli scapulæ, and splenius muscles.

=The Omo-trachelian Muscle= (Fig. 68, 13; Fig. 69, 17; Fig. 70,
20).--Also called the _acromio-trachelian_, _levator ventri
scapulæ_,[21] the _angulo-ventral muscle_, and the
_transverso-scapular_,[22] etc., this muscle is described by some
hippotomists as belonging to the mastoido-humeral, of which it then
forms its posterior or deep portion (see p. 153).

  [21] Ventri, because inserted into the inferior part of the spine of
       the scapula, towards the acromion--that is, on the ventral
       side--by contrast with the trapezius, which is attached higher up
       (dorsal side) on the same process.

  [22] Among the many names given to this muscle, Arloing and Lesbre
       recommend the adoption of the name 'transverse scapular' given by
       Straus-Durckheim, or 'transverse of the shoulder' (Arloing and
       Lesbre, 'Suggestions for the Reform of Veterinarian Muscular
       Nomenclature,' Lyons, 1898).

The omo-trachelian muscle is found in all mammalia, man alone excepted.
It is, however, sometimes found in the human being; but it then
constitutes an anomaly.

In the dog, pig, and ox, it arises from the inferior part of the spine
of the scapula, in the region of the acromion, and terminates on the
lateral portion of the atlas.

In the cat it is attached besides to the base of the occipital bone. It
is visible in the space limited by the trapezius and the
mastoido-humeral, the direction of which it crosses obliquely.

In the horse it appears to be blended in clearly defined fashion with
the mastoido-humeral. Attached below, like this latter, to the anterior
border of the humerus, it covers the scapulo-humeral angle; and is
attached by its upper portion to the transverse processes of the first
four cervical vertebræ.

We remember that the transverse processes are often, from their relation
with the trachea, known as the tracheal processes. Hence the word
'trachelian,' which forms part of the name of the muscle with which we
are now dealing.

By its contraction it helps to draw the anterior limb forwards.

When this muscle, as an abnormality, exists in man, it arises from
the clavicle or the acromion process, traverses the supraclavicular
fossa, and is inserted into the transverse processes of the atlas or
axis, or of both these vertebræ, or of the cervical vertebræ below
these latter. It is then known by the names of the _elevator of the
clavicle_ or _elevator of the scapula_, and, finally, as the
_cleido-omo-transversalis_ (Testut).[23]

  [23] L. Testut, 'Les anomalies musculaires chez l'homme expliquées par
       l'anatomie comparée,' Paris, 1884, p. 97. A. F. Le Double,
       'Traité des variations du système musculaire de l'homme et de
       leur signification au point de vue de l'anthropologie
       zoologique,' Paris, 1897, t. i., p. 235.

=The Levator Anguli Scapulæ= (Fig. 68, 15; Fig. 70, 23).--As we have
pointed out (p. 136), the levator anguli scapulæ, because of its
connections with the great serratus, is sometimes described with it. But
inasmuch as in human anatomy these two muscles are considered
separately, and that, in the superficial layer of muscles, they are seen
in different regions--the great serratus in the thoracic, and the
levator anguli scapulæ in the cervical--we prefer to study them
separately.

We remember that in man this muscle arises from the transverse processes
of the upper cervical vertebræ and is inserted into the superior portion
of the spinal border of the scapula, into the portion of this border
which is situated above the spine; it also contributes to the formation
of the floor of the supraclavicular region.

When it contracts, it draws the superior portion of the scapula forwards
and upwards, and causes a see-saw movement, for at the same time the
inferior angle of the scapula is directed backwards. Taking its fixed
point at the shoulder, it directly extends the neck if the muscle of one
side acts at the same time as that of the opposite; but if only one
muscle contracts it inclines the neck to the corresponding side.

It is to be noticed that during movements a little more active than the
ordinary the levator anguli scapulæ, as moreover the other muscles of
the neck do, becomes very distinct. We have, indeed, often remarked
that, apart from these movements, each time the support of one of the
fore-limbs is brought into requisition a brusque contraction of the
muscles of this region accompanies it.

This contraction gives the impression that, as on the one hand, each
support determines a momentary arrest of progression, a jolt, and on the
other hand, the head continues to be projected in the forward direction,
the latter should be retained. But it cannot be so except by an effort
in the opposite direction--that is to say, by the brusque contraction
which we have just pointed out.

Analogous contractions also take place in a man while running at the
beginning of each contact of the lower limbs with the ground.

We may add, apropos of this latter, that displacements of the head,
sometimes in very pronounced fashion, take place during simple walking,
and that every time one of the lower limbs is carried forwards the head
is projected in the same direction. These displacements, which we also
find take place in the horse in pacing, especially in the region of the
neck and head, seem then to have the effect of aiding the progression of
the body forwards.

They occur especially in animals when drawing a heavy load, and in
individuals whose walking movements are executed with difficulty.

It is necessary to repeat that, in these cases, the individual appears
to assist the movement of his body by the impetus which the projection
of his head forward determines, in order to add--and it is for this that
we have referred to the subject--that during the intervals between each
projection the head is carried backwards by a muscular contraction
similar to that above discussed.

=The Splenius= (Fig. 68, 14; Fig. 70, 22).--In man, this muscle is
attached in the median line to the inferior half or two-thirds of the
posterior cervical ligament, to the spinous processes of the seventh
cervical, and four or five upper dorsal vertebræ; it passes obliquely
upwards and outwards, becomes visible in the supraclavicular region,
passes under the sterno-cleido-mastoid, and proceeds to duplicate the
cranial insertions of this latter; and, further, the most external
fasciculi of this muscle are inserted into the transverse processes of
the atlas and the axis.

These separate superior attachments, and the division of the muscle
which results, have caused the splenius to be regarded as formed of two
portions: splenius of the head, and splenius of the neck.

In the horse, this muscle, which is of voluminous dimensions, arises
from the superior cervical ligament, and the spinous processes of the
first four or five dorsal vertebræ; thence it proceeds to be inserted
into the mastoid crest, and the transverse processes of the atlas and
three or four vertebræ following.

The region occupied superficially by the splenius is remarkable for the
prominence which this muscle, with the deeply-seated complexus, which is
equally bulky, determines at this level; it is situated above that
region of the neck, in which are seen in part the fasciculi of the
levator anguli scapulæ. It terminates above and in front in the ridge,
which is sometimes very pronounced, which the transverse processes of
the atlas make on each side of this part of the neck.

In the dog and the cat, the superior and anterior region of the neck is
thick and of rounded form, on account of the development which the
splenius presents in those animals; but it is covered by the
mastoido-humeral.

This latter relation is also found in the ox, but the splenius in this
case is but slightly developed.

When the splenius contracts it extends the head and neck, while
inclining them to its own side.

If the splenius of one side contracts at the same time as that of the
opposite, the extension takes place in a direct manner--that is to say,
without any modifying lateral movement.


Infrahyoid Muscles

Having studied the lateral surfaces of the neck, we must now examine the
anterior part of this region. Here, between the two sterno-mastoid
muscles, we find a space broader above than below, in which are situated
the larynx and the trachea, to the general arrangement of which is due
the cylindrical form which this region presents. This space corresponds
to that which in the neck of man is limited laterally by the
sterno-cleido-mastoid muscles, below by the fourchette of the sternum,
and above by the hyoid bone. In animals, as in man, it is called the
infrahyoid region.

The hyoid bone in quadrupeds is situated between the two rami or
branches of the lower jaw. Owing to this disposition, the region above
this bone, instead of having its surface projecting a little beyond the
inferior border of the maxillary bone, is depressed. This is especially
so in the horse. It is there that we find in this animal the region
known as the _trough_ (_auge_); the larynx corresponds to that part
known as the _gullet_.

The muscles which occupy the infrahyoid region are: the sterno-thyroid,
the sterno-hyoid, and the omo-hyoid. There is also a thyro-hyoid, but
because of its deep situation and its slight importance it offers no
interest from our point of view.

=Sterno-thyroid and the Sterno-hyoid Muscles.=--These two muscles, long,
narrow, and flat, arise from the anterior extremity of the sternum;
then, covering the anterior surface of the trachea, they proceed to
terminate, the one on the thyroid cartilage, and the other on the hyoid
bone. The sterno-hyoid is superficial; it covers the sterno-thyroid,
which, however, projects a little on its outer side.

=Omo-hyoid.=--This muscle does not exist in the dog or cat. It arises,
in the horse, from the cervical border of the scapula, where it blends
with the aponeurosis that envelops the subscapularis muscle, but in the
pig and the ox it arises from the deep surface of the mastoido-humeral
muscle. It is directed obliquely upwards and inwards, becoming
superficial at the internal border of the sterno-mastoid, and is
inserted into the hyoid bone.

The region in which are united the portion of the neck which we have
just studied and the neighbouring part of the thorax--that is, the
breast--has certainly, in our opinion, a form less expressive than the
corresponding region in man.

In the latter, indeed, the fourchette of the sternum, with the
hollow which it determines, the heads of the clavicles, and the
sterno-cleido-mastoid muscles, by the elevations which they produce, and
the trachea, by the situation which it occupies in the inferior part,
constitute a whole in which are admirably indicated, not only the forms
of the organs which constitute this region, but also the relations which
these organs have one with another; and, to a certain extent, their
respective functions.

In making an exception in the case of the ox, in which a fold of skin,
the _dewlap_, which passes from the neck to the breast, constitutes an
element of form which possesses some expressive value; in the horse and
in the dog, which possess no sternal fourchette and no heads of
clavicles, the bones and the muscles are found nearly on the same plane.
This produces a uniformity which is evidently inferior, from an
æsthetic point of view, to the modelling of the corresponding region of
the human body. Such, at least, is our impression.


Suprahyoid Muscles

As their name indicates, these muscles are found above the hyoid bone;
amongst those which should arrest our attention for a moment are the
mylo-hyoid and the digastric.

=Mylo-hyoid.=--This muscle, forming a sort of fleshy sling which
contributes in great measure to form the floor of the mouth, is situated
between the lateral halves of the inferior maxillary bone. Arising on
each side from the internal oblique line of the mandible, its fibres are
directed towards the median line, to be inserted posteriorly into the
hyoid bone, and, between this bone and the anterior part of the
mandible, into a median raphe which unites these latter.

=Digastric.=--This muscle arises from the styloid process of the
occipital bone and from the jugular process; it thence passes downwards
and forwards, and terminates variously, in different species. In the ox
and the horse it terminates in its anterior portion on the internal
surface of the inferior maxillary bone, close to the chin. But in the
horse a bundle of fibres is detached from the upper portion of the
muscle, to be inserted into the recurved portion of the jaw. It is to
this fasciculus that Bourgelat has given the name of '_stylo-maxillary
muscle_.'

In the pig, dog, and cat, the digastric differs more from the
corresponding muscle in man; it is not, as in the latter, formed of two
parts. The anterior portion only exists. This consists of a thick
muscular mass, which is inserted into the middle of the internal surface
of the lower jaw.

In the dog and cat it is clearly recognisable in the superficial layer
of muscles by the long and thick prominence which it produces below the
masseter, against the inferior border of the mandible (see pp. 235 and
237, the two figures showing the myology of the head of the dog).

By its contraction, it draws the lower jaw downwards and backwards.

=Panniculus of the Neck.=--This very thin muscle, which cannot be
recognised on the exterior, calls for little notice.

We shall merely point out that it duplicates the skin of the cervical
region; but as the latter is only slightly adherent to it, the
panniculus of this region seems rather destined to maintain in position
the muscles which it covers than to displace the cutaneous covering.

We recall the fact that in man, on the contrary, the muscle is very
evident at the instant of its contraction, and, for this reason, it
presents a very great interest with regard to external modelling, and it
plays an important part in the expression of the physiognomy.


MUSCLES OF THE ANTERIOR LIMBS


Muscles of the Shoulder

=Deltoid= (Fig. 68, 16, 17; Fig. 69, 18; Fig. 70, 24).--This is the
first muscle we study in connection with the shoulder in human anatomy.
Indeed, its wholly superficial position, and especially the manner in
which it is separated from the surrounding muscles, its volume, and its
characteristic modelling, give it such an importance that, from the
didactic point of view, there is every indication for commencing with
this muscle in studying the region to which it belongs. If, in regard to
quadrupeds, we also commence with it, it is merely in deference to the
spirit of method, and for the sake of symmetry; for it is far from
presenting, in the latter, characters so distinctive and so clearly
defined.

It is necessary to remark, at the outset, that in quadrupeds, on account
of the absence or slight development of the clavicle, the clavicular
portion of this muscle is, as we have shown, united to bundles of the
same kind belonging to the sterno-cleido-mastoid and trapezius to form
the mastoido-humeral (see p. 151). There exists, therefore, in an
independent form, the scapular portion only.

It is this latter which, by itself alone, forms the deltoid of
quadrupeds, a muscle known, in veterinary anatomy, as _the long abductor
of the arm_.

In the dog and the cat it consists of two parts, one of which arises
from the spine of the scapula; the other from the acromion process.
Thence it passes to the crest of the humerus, which limits the
musculo-spiral groove anteriorly, to be attached at a point which is
found, as in other quadrupeds, to be the homologue of the human deltoid
impression, or deltoid [V], of the human humerus.

In the ox, in which the acromion process, which is very rudimentary,
does not attain the level of the glenoid cavity, the acromion portion is
but slightly marked off from that which takes its origin from the spine
of the scapula.

Still, in the horse, which is completely deprived of an acromion
process, the deltoid muscle is correspondingly divided into two parts,
separated from one another by superficial interstices, but of which the
arrangement differs from that of the portions above indicated; one part,
the posterior, arises above from the superior part of the posterior
border, and the postero-superior angle of the scapula (exactly as if, in
man, certain fasciculi of the deltoid took their origin from the
axillary border and inferior angle of the scapula); the other, anterior,
arises from the tuberosity of the spine of the same bone. The two parts,
united inferiorly, proceed to be inserted into the deltoid impression or
infratrochiterian crest of the humerus.

It is necessary to add that the deltoid is inserted into the humerus,
above the insertion of the mastoido-humeral.

This muscle flexes and abducts the humerus, and also rotates it
outwards.

With regard to the other muscles of the human shoulder, subscapularis,
supraspinatus, infraspinatus, teres minor and teres major, they are also
present in quadrupeds, but in a form more elongated, as the scapula has
its dimensions more extended from below upwards--that is, from the
glenoid cavity towards the superior or spinal border.

=Subscapularis.=--This muscle occupies the subscapular fossa, from which
it takes its origin, leaving free the superior part where the surface is
found, to which are attached the serratus magnus and the levator anguli
scapulæ. It passes towards the arm, to be inserted into the small
tuberosity of the humerus. It is an adductor of the arm.

The subscapularis does not offer any interest from the point of view of
external form, for it is completely covered by the scapula.

We speak of it, however, because we mention it in human anatomy, and
that it affords us here a new opportunity of bringing into prominence
the differences which exist in connection with the mobility of the
shoulder.

We remember that in man, when the arm is abducted, and then raised a
little above the horizontal, the scapula see-saws, is separated, to a
certain extent, from the thoracic cage inferiorly and externally, and
that, on the superficial layer of muscles, we are then able to see in
the bottom of the armpit, at the level of the deep portion of the
posterior wall of the latter, a small part of the subscapularis muscle.

In the animals with which we are here occupied it is not the same; for
they are incapable of performing with their fore-limbs a movement
analogous to that to which we have just referred, the humerus in their
case being retained in contact with the trunk by the muscular masses
which surround it.

=Supraspinatus= (Fig. 68, 19; Fig. 70, 25; Fig. 72, 7).--This muscle, as
its name indicates, occupies the supraspinous fossa--that is to say,
that which, by reason of the direction of the scapula in quadrupeds, is
situated in front of rather than above the spine. It arises from this
fossa; and, further, from the external surface of the cartilage which
prolongs the scapula upwards in solipeds and ruminants. It projects more
or less beyond the supraspinous fossa in front.

After passing downwards towards the humerus, it is inserted into the
summit of the great tuberosity or trochiter--that is to say, to a part
of this osseous prominence which represents the anterior facet of the
great tuberosity of the human humerus, into which, as we know, the
corresponding muscle is inserted.

In solipeds and ruminants it is inserted, by a second fasciculus, into
the small tuberosity.

In the pig and the horse its anterior border is in relation with the
terminal portion of the sterno-prescapular anterior portion of the small
or deep pectoral.

The supraspinatus, which in man is completely covered by the trapezius,
is partly visible in the superficial layer of the cat, dog, pig, and
horse, in the lower part of the space limited by the mastoido-humeral
and the trapezius. It is crossed by the scapulo-trachelian.

It is, in the ox, completely covered by these muscles, but its form,
notwithstanding this, is easily discerned by the prominence which it
produces. When it contracts, the supraspinatus muscle carries the
humerus into the position of extension.

=Infraspinatus= (Fig. 68, 20; Fig. 72, 8).--This muscle, which occupies
the infraspinous fossa, which, in quadrupeds, is situated behind the
spine of the scapula, arises from the whole extent of this fossa, and in
solipeds and ruminants encroaches on the cartilage of prolongation. Its
fibres are directed downwards and forwards, to be inserted into the
great tuberosity of the humerus--the trochiter--below the insertion of
the supraspinatus.

It is completely covered (ox and horse), or in part only (cat and dog),
by the portion of the deltoid which arises from the spine of the
scapula; nevertheless, its presence is revealed by the prominence which
it produces.

It is an abductor and external rotator of the humerus.

In connection with this muscle, which, as we have just pointed out, is
less seen in the superficial muscular layer than the supraspinatus, we
will draw attention to the fact that this arrangement is exactly the
reverse of that which is found in the human shoulder. In this latter it
is the supraspinatus which is not visible; while, on the contrary, the
infraspinatus is uncovered in a considerable part of its extent. We
further notice that it is accompanied by the teres minor, and that the
teres major, situated inferiorly, forms with these two muscles a fleshy
mass which, below, ends on the superior border of the great dorsal
muscle.

In quadrupeds, in which the infraspinatus is so slightly visible, the
teres major and minor are not found at all in the superficial muscular
layer.

Accordingly, we will say but few words about them.

[Illustration: FIG. 72.--MYOLOGY OF THE HORSE--SHOULDER AND ARM: LEFT
SIDE, EXTERNAL SURFACE.

1, Cartilage of prolongation of the scapula; 2, tuberosity of the spine
of the scapula; 3, superior extremity of the humerus; 4, inferior
extremity of the humerus; 5, radius; 6, ulna; 7, supraspinatus muscle;
8, infraspinatus; 9, teres minor; 10, biceps; 11, tendon of the biceps
passing over the anterior surface of the superior extremity of the
humerus; 12, brachialis anticus; 13, triceps, long head; 14, external
head of the triceps divided; 15, external head of the triceps reflected,
in order to expose the anconeus; 16, region normally occupied by the
external head of the triceps; 17, anconeus.]

=Teres Minor= (Fig. 72, 9).--This muscle, also called in veterinary
anatomy _the short abductor of the arm_, arises from the posterior
border of the scapula (the external border in man), and is inserted
below the great tuberosity of the humerus, between the attachments of
the infraspinatus and deltoid.

It is covered by the deltoid and the infraspinatus.

=Teres Major.=--This muscle is known to veterinarians as _the abductor
of the arm_; it arises from the postero-superior angle of the scapula
(the inferior angle of the human scapula), from which it passes to be
inserted into the internal surface of the humerus.

It is covered by the latissimus dorsi and the posterior muscular mass of
the arm.

In brief, for the better understanding of the relations of the teres
major and minor muscles in quadrupeds, we may fancy the corresponding
muscles in man modified in the following manner: The infraspinatus,
thicker, covering the teres minor; latissimus dorsi, more extended in
its superior part, covering a large proportion of the teres major. As to
the relations of the teres minor with the deltoid, they exist in man,
seeing, in this case, the same muscle is, in its external portion,
covered by this latter. With regard to the relations of the teres major
with the posterior muscular mass of the arm, they also exist in man,
since the external surface of this muscle is covered by the triceps.

These modifications are sufficient to render the small and large teres
muscles completely invisible in the superficial layer.

The muscles of the shoulder which we have just been studying fulfil,
with regard to the articulation which they surround, the function of
active ligaments. This rôle is made necessary by the laxity of the
scapulo-humeral capsule--a laxity which renders it incapable by itself
of maintaining the bones in contact at this joint.

The same condition exists in man.

=Panniculus Muscle of the Shoulder.=--This thin muscle covers, as its
name implies, the region of the shoulder, and is the continuation
forward of the panniculus muscle of the trunk.

It arises, by its superior part, from the region of the withers and from
the superior cervical ligament; thence its fibres descend directly
towards the elbow, to terminate at the level of the region of the
forearm.

The muscle is not found in the pig or in the carnivora.


Muscles of the Arm

We should remember, at the outset, that in man the muscles of the arm
are divided into two groups: one anterior, which contains the biceps,
brachialis anticus, and the coraco-brachialis; the other, posterior,
which is constituted by a single muscle, the triceps.

In animals, we find them in the same number and arranged in analogous
fashion--that is to say, in two groups--with respect to the bone of the
arm. But then we find that they have undergone a transformation with
regard to their length, and it is the change of general aspect which
results from this modification that we proceed to examine.

We know that in quadrupeds, and especially in the domestic animals, the
humerus is relatively short in proportion to the forearm. We have
already seen, in dealing with the bones, that whilst in the human
species the humerus is longer than the forearm, in the dog and cat these
two segments of the fore-limb are of equal length, and that the humerus
of the horse is, on the contrary, much shorter. Now, let us suppose the
human humerus to be shorter than it is in reality; the anterior muscles
undergoing, very naturally, the same reduction, will be uncovered only
slightly by those above--the deltoid and the great pectoral--or will
remain completely hidden by them. Thus would be found realized the
disposition which we meet with in quadrupeds of the muscles of this
region.

With regard to the posterior muscular mass of the arm, it does not
undergo the same change. The muscle which constitutes it--the triceps
cubiti--occupies, on the contrary, a greater area. Let us suppose,
further--for it is the best method of comprehending the homologies which
now occupy our attention--the humerus of man to be shortened as before,
and directed downwards and backwards (as in quadrupeds), this bone would
form an acute angle with the axillary border of the scapula. Let us
suppose also that the long portion of the triceps, instead of arising
solely from the superior part of this axillary border, is attached to
the whole length of the latter, and that the triceps fills the whole
interior of the angle formed by the arm and the shoulder. We then shall
have an idea of what the triceps is in quadrupeds. It is necessary to
add that the general resemblance would be still more complete if the arm
were firmly supported by the side of the thorax, because in quadrupeds
it occupies an analogous position, determined by the arrangement of the
muscles which, proceeding from the trunk and neck, are attached to it.


Anterior Region

=Biceps Cubiti= (Fig. 68, 21; Fig. 72, 10, 11).--This muscle, also
called _the long flexor of the forearm_, does not merit the name except
by its analogy with the corresponding muscle in man. Indeed, in the
domestic animals it is not divided into two parts; it is represented by
a single fasciculus, long and fusiform, situated on the front of the
humerus, and directed obliquely downwards and backwards, as the latter,
on its part, is also inclined.

It arises above from a tubercle at the base of the coracoid process,
which surmounts the glenoid cavity of the scapula. Its tendon, which is
highly developed in the solipeds, occupies the bicipital groove. We
remember that in these latter the groove in question is divided into two
channels by a median prominence.

The tendon in which the muscle ends is inserted into a tuberosity,
situated on the internal surface of the superior extremity of the
radius--the bicipital tuberosity. In the pig, the cat, and the dog,
there is detached from the tendon to which we have just referred a
fasciculus of the same nature, which, after having wound round the
radius, is inserted into the internal surface of the ulna, towards the
base of the olecranon process. From the inferior part of the muscle
arises a fibrous band, comparable to the aponeurotic expansion of the
human biceps; but, instead of passing downwards and inwards, as does the
latter, it terminates on the muscular mass which constitutes the
antero-external part of the forearm.

The biceps is not seen in the superficial layer, except in the dog and
cat (in which the humerus is, in fact, proportionately long); and even
in them only to the slightest extent. It is covered partly in these
latter, and completely in other animals, by the great pectoral and the
inferior portion of the mastoido-humeral--that is to say, that part of
the latter which represents the whole of the clavicular fibres of the
human deltoid.

The biceps is a flexor of the forearm on the arm. It also contributes to
the movement of extension of the humerus.

=Brachialis Anticus= (Fig. 68, 22; Fig. 69, 19; Fig. 70, 27; Fig. 72,
12).--In veterinary anatomy further designated as _the short flexor of
the forearm_, this muscle, which is thick, occupies the musculo-spiral
groove, and arises from it, reaching upwards to just below the head of
the humerus. But it does not, as in man, extend to the internal surface
of the bone.

Situated on the outside of the biceps, it is directed towards the
forearm, and terminates by a flattened tendon, which, dividing into two
slips, passes below the bicipital tuberosity, on the internal surface of
the radius, into which one of these slips is inserted, while the other
proceeds to terminate on the ulna.

The inferior half of this muscle is visible on the superficial layer, in
the space limited posteriorly by the triceps brachialis, and below by
the muscles of the forearm, which correspond to the external muscles of
the human forearm, and in front by the great pectoral and the
mastoido-humeral. It is in the upper part of the interspace which
separates these latter from the brachialis anticus that the deltoid
insinuates itself to proceed to its insertion into the humerus.

These relations precisely recall those which we meet with when we
examine the external surface of the human arm, with this difference,
however--that in the latter the anterior brachialis anticus is
extensively related, in front, to the biceps. However, in animals it is
not absolutely the same, since, as we have shown above, the biceps is
covered, more or less completely, by the mastoido-humeral and the great
pectoral.

The brachialis anticus flexes the forearm on the arm.

=Coraco-brachialis.=--In man this muscle, which occupies the superior
half, or third, of the internal surface of the humerus, is visible only
when the arm is abducted, and then especially when it approaches the
vertical position; indeed, it is only in this attitude that the region
which it occupies is accessible to view.

But an analogous attitude not being possible in domestic animals, in
which the arm is fixed along the corresponding parts of the trunk, the
result is that the coraco-brachialis is always covered, and that,
consequently, it presents nothing of interest from our point of view. We
speak of it, then, merely in order to complete the series of the muscles
of the anterior surface of the arm, among which we rank it, in spite of
the fact that in veterinary anatomy it is described as a muscle of the
shoulder.

It arises above from the coracoid process, and thence passes downwards
towards the internal surface of the humerus into which it is inserted,
more or less high up, according to the species. The coraco-brachialis is
an adductor of the arm.


Posterior Region

=Triceps Cubiti= (Fig. 68, 23, 24; Fig. 69, 20, 21; Fig. 70, 28, 29;
Fig. 72, 13, 14, 15, 16).--This muscle, which is voluminous in the
quadrupeds with which we are here concerned, fits more or less
completely the angular space between the scapula and the humerus. Its
bulk forms a thick prominence, which surmounts the elbow and the
forearm.

We should say, with regard to this mass, that if the deltoid does not
constitute in quadrupeds a prominence sufficient to remind one of that
which this muscle produces in man, the triceps, in producing an
analogous elevation, seems to replace in the general form of the body
the relief which the deltoid is incapable of producing.

The triceps is divided into three portions, which, as in man, have the
names middle, or long head; external and internal heads. But that which
renders the nomenclature a little complicated is that veterinary
anatomists have given other names to these three parts: that of _great
extensor of the forearm_ (caput magnum) to the long head; _the short
extensor of the forearm_ (caput parvum) to the external head; and of
_medium extensor of the forearm_ (caput medium) to the internal.[24]

  [24] Other names given by certain authors to the parts of this muscle
       which we have just enumerated still further complicate this
       nomenclature.

The long head is further designated by them under the names of the
_long_ or _great anconeus_; the _external head_ under those of _external
anconeus_, or _lateral_ or _short anconeus_; whilst the internal head
becomes the _internal anconeus_, or _median_.

It is more especially the long portion and the external head which,
being visible on the external surface of the arm, contribute to the
external form.

The long portion, which is triangular in shape and of considerable
development, arises in the cat and the dog from the inferior half or
two-thirds of the posterior border of the scapula (axillary border);
from the whole extent of that border as far as the superior posterior
angle in the pig, the ox, and the horse; it then passes downwards
towards the articulation of the elbow, to terminate in a tendon which is
inserted into the olecranon process. The portion of this muscle which is
next the scapula is covered by the deltoid.

The external head, situated below the long portion, is directed
obliquely downwards and backwards. It arises from the curved crest
which, from the deltoid impression of the humerus, is directed upward to
meet the articular head of the same bone. This crest limiting the
musculo-spiral groove superiorly, and the brachialis anticus arising
from the whole extent of this groove, the result is that at this level
the external head is in relation with the brachialis anticus. From this
origin it is directed towards the elbow, to be inserted into the
olecranon, either directly or by the medium of the tendon of the long
portion. The part of this muscle which arises from the humerus is
covered by the deltoid.

As for the internal head (Fig. 76, 4), which, in the superficial layer,
is only visible in its inferior part, on the internal aspect of the arm
in those animals in which the elbow is free of the lateral wall of the
thorax (the dog and the cat, for example), it arises from the internal
surface of the humerus, and thence proceeds to be inserted into the
olecranon.

The triceps extends the forearm on the arm.

A fourth muscle exists, which veterinary anatomists include in the study
of the three portions of the triceps which we have just been discussing,
in giving it the name of _small extensor of the forearm_. But, as this
muscle is no other than the anconeus, and as, in human anatomy, we
describe the latter, according to custom, in connection with the
forearm, it is when on the subject of the latter that we will concern
ourselves with it. This grouping of muscles cannot fail to give greater
clearness to the description of the muscles of these regions.

=The Supplemental or Accessory Muscle of the Latissimus Dorsi= (Fig. 76,
2; Fig. 77, 1).--Because of the relations, to which we have already
referred (see p. 142), of this muscle with the triceps cubiti, its
description very naturally follows that of the latter.

Indeed, this supplementary muscle of the great dorsal is further
designated in zoological anatomy under the name of _long extensor of the
forearm_; and this name indicates that its study may be united to that
of the triceps.

Situated on the internal surface of the arm, it arises from the external
aspect of the tendon of the latissimus dorsi; it is very highly
developed in the horse, in which it also arises from the posterior
border (axillary) of the scapula; then, covering in part the internal
head of the triceps and also the long portion, on the superior border of
which it is folded, it proceeds to be inserted into the olecranon
process and the anti-brachial aponeurosis.

It extends the forearm on the arm. Further, it makes tense the
aponeurosis into which it is inserted; this explains the name of _tensor
of the fascia of the forearm_, which is sometimes given to it.

It seems to us interesting to add that, abnormally, we sometimes find in
man an analogue of this muscle. It is given off from the latissimus
dorsi, near the insertion of the latter into the humerus; it accompanies
the long head of the triceps and becomes fused with it. Sometimes it is
inserted into the olecranon process, at other times into the
antibrachial aponeurosis or the epitrochlea. It is on account of its
insertion into the last-mentioned, in some cases, that it is also
designated by the name of _dorso-epitrochlear_ muscle.[25]

  [25] L. Testut, 'Anomalies musculaires chez l'homme expliquées par
       l'anatomie comparée,' Paris, 1884, p. 118. A. F. Le Double,
       'Traité des variations du système musculaire de l'homme et de
       leur signification au point de vue de l'anthropologie
       zoologique,' Paris, 1897, t. i., p. 203. Édouard Cuyer,
       'Anomalies musculaires' (_Bulletins de la Société
       Anthropologique_, Paris, 1893).


Muscles of the Forearm

Before commencing the special examination of each of the muscles of this
region, it is absolutely indispensable to consider their general
arrangement, and to determine very clearly how we should study them. We
are too well convinced of the importance of this preliminary examination
to dismiss it without entering rather fully into it. Indeed, the region
on the myological study of which we are now entering is, unquestionably,
one of the most complicated with which we have to deal. We know besides,
in regard to the study of the forearm in man, how much a definite method
is necessary in order that the arrangement of the muscles of this region
be fixed in the memory, and that we are unable to obtain this result
otherwise than by grouping the twenty muscles which constitute it in
clearly defined regions.

We also know that these muscles are first studied with the forearm in
the position of supination, and that it is only when they are well known
after having considered them in this position that we are able to
analyze and comprehend their forms when it is in pronation.

Now, as we have pointed out in the section on osteology (see p. 34), the
forearm in quadrupeds is always in the position of pronation. Should we,
then, in order to maintain the symmetry with human anatomy, first study
the forearm in the position of supination? Evidently not. Besides the
fact that this would in some cases be impossible since--as in the horse,
for example--the radius and ulna are fused together, we should not gain
any advantage; this position being never completely realizable even in
those quadrupeds which have the radius relatively movable--as, for
example, in the cat.

Accordingly, it is pronation which here, in connection with animals,
becomes the standard attitude from the point of view of description.
This is why, supposing that the reader knows well the muscles of the
human forearm in the position of supination, we should recall what is
the general arrangement occupied by these muscles when it is in
pronation.

The fore-limb, being viewed on its anterior surface, presents above the
anterior aspect of the region of the elbow; but below, it is the
posterior surface of the wrist which is seen. Consequently, in the
superior part, we see the external and anterior muscles limiting the
hollow in front of the elbow; interiorly are found the posterior
muscles.

The long supinator, passing obliquely downwards and inwards, divides, in
fact, the forearm into two parts: one supero-internal, the other
infero-external. In the first we see, but to an extent less and less
considerable, the pronator teres, the flexor carpi radialis, the
palmaris longus, and the flexor ulnaris; as to the flexors of the
digits, on account of the rotation of the radius, they are only visible
on the opposite surface--that is to say, on the surface of the wrist,
which is now posterior. In the second part we see the two radial
extensors, the common extensor of the fingers, the proper extensor of
the little finger, and the ulnar extensor which, inferiorly, remains
behind, by reason of the position of the ulna being unchanged, whilst
the anconeus is wholly posterior, since the direction of the elbow is
not modified. We also find, in this region, the long abductor of the
thumb, the short extensor of the thumb, the long extensor of the thumb,
and the special extensor of the index-finger, in the region where these
deep muscles become superficial.

So that, to summarize, the external and posterior muscles occupy the
anterior and external regions of the forearm, whilst the anterior
muscles occupy rather the internal and posterior. It is in regarding
them after this manner--that is to say, arranged in these two
regions--that we proceed to study these muscles in quadrupeds.


Anterior and External Region

=Supinator Longus.=--We know that this muscle, which is especially a
flexor of the forearm on the arm, plays, notwithstanding the name which
has been given it, a part of but little importance in the movement of
supination.

It acts slightly, however, as a supinator, for, being very oblique
downwards and inwards at the time of pronation, it is able, while
tending to resume its vertical direction, to carry the radius outwards;
it places, in fact, the forearm in a position midway between pronation
and supination.

We have just recalled these details, in order that it may be more easy
to understand why it does not exist in animals in which the radius and
ulna are fused together (horse, ox); and why, on the other hand, we find
traces of it in the cat and the dog, in which the radius--to a slight
extent, it is true--is able to rotate on the ulna. This displacement
being a little more considerable in the felide, the long supinator is a
little further developed than it is in the canine species; but,
notwithstanding, it is only rudimentary.

The long supinator arises, above, from the external border of the
humerus; thence, in the form of a very narrow fleshy band, it passes
obliquely downwards and inwards, to be inserted into the inferior part
of the internal surface of the radius.

It assists in turning the radius outwards and placing it in front of the
ulna, the movement of supination being capable of being but little
further extended.

=First and Second External Radial Muscles=: _Extensor carpi radialis
longior and brevior_ (Fig. 73, 8; Fig. 74, 8, 9; Fig. 75, 8, 9).--Fused
together, these muscles form by their union what veterinary anatomists
call _the anterior extensor of the metacarpus_. But we should add that
these two muscles are united so much the more intimately as we examine
them in passing successively from the cat to the dog, pig, ox, and
horse. Thus, in the cat they are often distinct; in the dog, they unite
only at the level of the middle third of the radius, and interiorly they
have two tendons; in the pig, the ox, and the horse they are completely
united, and there exists but a single tendon.

The _anterior extensor of the metacarpus_, which is situated behind the
long supinator when the latter exists, occupies the external aspect of
the forearm; its well-defined form absolutely recalls the prominence on
the superior part of the external margin of the human forearm.

It arises superiorly from the portion of the external border of the
humerus which is situated above the epicondyle and behind the
musculo-spiral groove. Its fleshy mass appears in the angular space
bounded by the brachialis anticus and the triceps. The superior portion
is covered by the external head of the triceps; yet, in the dog, the
superior portion of its humeral attachment is the only part so covered.
This muscle is directed forward and downwards; it is also inclined a
little inwards in such manner as to proceed to occupy the anterior
aspect of the forearm.

Its fleshy belly is narrowed below, and, towards the inferior part of
the forearm, is continued by a tendinous portion which is situated on
the anterior surface of the carpus, after having traversed the median
groove of the inferior extremity of the radius.

In the cat and the dog, in which the union of the two radial extensors
is incomplete, the two tendons are inserted into the front of the base
of the second and third metacarpal bones; consequently, as in man, into
the metacarpals of the index and middle fingers.

In the ox, the tendon, which is single, is inserted into the internal
and anterior half of the superior extremity of the principal metacarpal.

In the pig, this tendon is attached to the base of the large internal
metacarpal.

In the horse, the corresponding tendon is attached to a tubercle which
is situated on the anterior surface of the base of the principal
metacarpal, a little internal to the median plane of the latter.

[Illustration: FIG. 73.--MYOLOGY OF THE DOG: LEFT ANTERIOR LIMB,
EXTERNAL ASPECT.

1, Mastoido-humeralis; 2, biceps; 3, brachialis anticus; 4, triceps,
long portion; 5, triceps, external head; 6, olecranon process; 7,
epicondyle; 8, radialis muscles (anterior extensor of the metacarpus);
9, extensor communis digitorum (anterior extensor of the phalanges); 10,
extensor minimi digiti (lateral extensor of the phalanges, or common
extensor of the three external digits); 11, posterior ulnar (external
flexor of the metacarpus); 12, pisiform bone; 13, anconeus; 14, extensor
ossis metacarpi pollicis and extensor primi internodii pollicis (oblique
extensor of the metacarpus); 15, radius; 16, anterior ulnar (oblique
flexor of the metacarpus); 17, external border of the hypothenar
eminence (abductor of the little finger).]

In order to properly understand and remember the respective positions
occupied by these inferior insertions, it must be remembered that the
human forearm being in the position of pronation, the tendons of the
radials are attached to the bases of the metacarpals nearest to the
thumb--that is to say, those occupying an internal position as regards
the fourth and fifth metacarpals.

As its name indicates, this muscle extends the metacarpus. Consequently
it is, in the horse, an extensor of the canon-bone.

It is also an adductor of the hand in those animals (cat, dog) in which
the radio-carpal articulation, analogous in form to the corresponding
articulation in man, permits lateral movements of the hand on the
forearm. The union of the fleshy bodies of the two radials is sometimes
found in the human species.

=Supinator Brevis.=--As in the case of the long supinator, the short
supinator is found only in animals in which the radius can be rotated to
a greater or less extent around the ulna; therefore this muscle is not
found in the pig, the ox, or the horse; but it forms part of the forearm
of the cat and the dog.

Deeply situated at the region of the elbow, the short supinator has
little interest for us. All that we will say of it is that it goes from
the external part of the inferior extremity of the humerus to the
superior part of the radius; and that it is, in carnivora, the essential
agent in the production of the movement of supination.

=Extensor Communis Digitorum= (Fig. 73, 9, 10, 11; Fig. 74, 10, 11,
12).--Also named in veterinary anatomy the _anterior extensor of the
phalanges_, this muscle is situated external to and behind the anterior
extensor of the metacarpus already described.

In the human being, the common extensor of the fingers springs, in its
superior part, from the bottom of a depression, situated on the outer
side of and behind the elbow, and limited in front by the muscular
prominence which the long supinator and the first radial extensor form
at that level. At the bottom of this hollow or fossette is found the
epicondyle, which gives origin, amongst other muscles, to the common
extensor of the fingers. It is necessary to add that it is most
prominently visible during supination, and that it tends to be effaced
during pronation.

[Illustration: FIG. 74.--MYOLOGY OF THE OX: LEFT ANTERIOR LIMB, EXTERNAL
ASPECT.

1, Mastoido-humeralis; 2, pectoralis major; 3, deltoid; 4, brachialis
anticus; 5, triceps; 6, triceps, external head; 7, olecranon; 8, radial
extensors (anterior extensor of the metacarpus); 9, insertion of the
tendon of the anterior extensor of the metacarpus to the tubercle of the
superior extremity of the principal metacarpal; 10, 11, extensor
communis digitorum (10, proper extensor of the inner digits; 11, common
extensor of the two digits); 12, tendon of the common extensor of the
two digits; 13, band of reinforcement from the suspensory ligament of
the fetlock; 14, external tuberosity of the superior extremity of the
radius; 15, extensor minimi digiti (proper extensor of the external
digit); 16, tendon of the proper extensor of the external digit; 17,
posterior ulnar (external flexor of the metacarpus); 18, pisiform; 19,
extensor ossis metacarpi pollicis and extensor primi internodii pollicis
(oblique extensor of the metacarpus); 20, ulnar portion of the deep
flexor of the toes; 21, tendon of the superficial flexor of the toes
(superficial flexor of the phalanges); 22, tendon of the deep flexor of
the toes (deep flexor of the phalanges); 23, suspensory ligament of the
fetlock.]

An analogous arrangement is met with in animals. But the muscular
prominence is formed by the united radial extensors, and the fossette,
because of the permanent pronation of the forearm, is scarcely
recognisable. Likewise, with regard to the dog, we may say that it does
not exist, on account of the prominence which the epicondyle forms in
that animal (Fig. 73, 7).

In connection with this prominence of the epicondyle, it is interesting
to add that this detail recalls the relief which the same process
produces on the external aspect of the human elbow when the forearm is
flexed on the arm. We know that, in this case, the epicondyle is
exposed, because the muscles which mask it in supination (long supinator
and long radial extensor) are displaced and set it free during flexion.
But, in the dog, as in other quadrupeds besides, the forearm is, in the
normal state, flexed on the arm; the latter being oblique downwards and
backwards, and the former being vertical. Further, the epicondyle is
well developed.

The muscle with which we are now occupied, long and vertical in
direction, arises from the inferior part of the external border of the
humerus (there it is covered by the anterior extensor of the metacarpus,
from which it is freed a little lower down) and from the external and
superior tuberosity of the radius. In the carnivora, it arises from the
epicondyle. Its fleshy body is fusiform in shape, becomes tendinous in
the lower half of the forearm, and then divides into a number of slips,
varying in number according to the species; this division is correlated
to that of the hand--that is to say, with the number of the digits.
Before reaching this latter, the common extensor of the digits passes
through the most external groove on the anterior surface of the inferior
extremity of the radius.

[Illustration: FIG. 75.--MYOLOGY OF THE HORSE: LEFT ANTERIOR LIMB,
EXTERNAL ASPECT.

1, Mastoido-humeral; 2, pectoralis major; 3, deltoid; 4, brachialis
anticus; 5, triceps, long head; 6, triceps, external head; 7, olecranon;
8, radial extensors (anterior extensor of the metacarpus); 9, insertion
of the tendon of the anterior extensor of the metacarpus into the
tubercle of the superior extremity of the principal metacarpal; 10,
extensor communis digitorum (anterior extensor of the phalanges); 11,
tendon of the anterior extensor of the phalanges; 12, reinforcing band
arising from the suspensory ligament of the fetlock; 13, external
tuberosity of the superior extremity of the radius; 14, extensor minimi
digiti (lateral extensor of the phalanges); 15, tendon of the lateral
extensor of the phalanges; 16, fibrous band which this latter receives
from the tendon of the anterior extensor of the phalanges; 17, fibrous
band which the same tendon receives from the carpal region; 18,
posterior ulnar (external flexor of the metacarpus); 19, pisiform; 20,
extensor ossis metacarpi pollicis and extensor primi internodii pollicis
(oblique flexor of the metacarpus); 21, ulnar portion of the deep flexor
of the digits; 22, flexor digitorum profundus; 23, 23, tendon of the
flexor digitorum sublimis (superficial flexor of the phalanges); 24, 24,
tendon of the flexor digitorum profundus (deep flexor of the phalanges);
25, sesamoid prominence; 26, suspensory ligament of the fetlock; 27,
external rudimentary metacarpal.]

In the cat and the dog, the four tendons which result from the division
of the principal tendon go to the four last digits, and each of them is
inserted, as in the human species, to the second and third phalanges.

In the pig, the anterior extensor of the phalanges is rather complicated
in its arrangement. Its fleshy body is divided into four bundles
terminated by tendons, which in turn divide and join certain digits;
whence the special names given to each of these fasciculi, commencing
with the most internal, of: _proper extensor of the great inner toe_;
_common extensor of the two inner toes_; _common extensor of the two
outer toes_; and _proper extensor of the great outer toe_.

In the ox, the same muscle is divided into two bundles: the internal
proceeds to the internal toe, the external is common to the two toes.

In the horse, the tendon of the anterior extensor of the phalanges is
divided into two parts of unequal bulk. The smaller of these tendinous
slips, which is the more external, unites at the level of the superior
part of the metacarpus with the tendon of the muscle which we are about
to study in the following paragraph (Fig. 75, 16). The larger, after
having reached the anterior surface of the digit, is attached to the
anterior aspect of the first and second phalanges, and then forms a
terminal expansion which is inserted into the pyramidal eminence of the
third.

At the level of the first phalanx this tendon receives on each of its
lateral aspects a strengthening band, which proceeds from the terminal
extremity of _the suspensory ligament of the fetlock_,[26] and crosses
obliquely downwards and forwards over the surface of the first phalanx
to join the extensor tendon (Fig. 75, 12).

  [26] See p. 200 for a description of this ligament.

A similar arrangement is found in the ox.

This band is noticeable under the skin which covers the lateral aspects
of the ham.

As the name indicates, this muscle extends the phalanges, one upon the
other. It also contributes to the extension of the hand, as a whole, on
the forearm.

=Extensor Minimi Digiti= (Fig. 73, 10; Fig. 74, 15, 16; Fig. 75, 14,
15).--This muscle, _the lateral extensor of the phalanges_ of veterinary
anatomy, situated on the external surface of the forearm, behind the
common extensor of the digits, arises, as a rule, from the epicondyle
(dog, cat), or from the external surface of the superior extremity of
the radius (horse). The tendon succeeding to the fleshy body appears
towards the lower third of the forearm, and at the level of the wrist
lies in a groove analogous to that which in man is hollowed out for the
passage of the corresponding tendon at the level of the inferior
radio-ulnar articulation. This groove corresponds to the same
articulation in animals in which the ulna is well developed, such as the
dog and the cat; but it belongs to the radius when the inferior
extremity of the ulna does not exist--for example, in the horse. Indeed,
in this animal the groove in question is found on the external surface
of the carpal extremity of the radius.

In the dog, the tendon is divided into three parts, which, crossing
obliquely the tendons of the common extensor of the digits, pass to the
three external digits, to be inserted by blending with the corresponding
tendons of the latter into the third phalanges of those digits.

Thus is explained the name of _common extensor of the three external
digits_ which is sometimes given to this muscle.

In the cat, there is a fourth tendon, which passes to the index-finger,
so that the name _common extensor of the four external digits_ is in
this case legitimate, and the lateral extensor of the phalanges is also
a common extensor, as is the anterior extensor of the phalanges, or
common extensor of the digits.

In the pig, the tendon, which is single, is inserted into the external
digit, for which reason it has received the name of the _proper extensor
of the small external digit_. This muscle is, then, really the homologue
of that which exists in the human species.

In the ox, it is called the _proper extensor of the external digit_; it
is as thick as the common extensor.

Finally, in the horse, the muscle is little developed. Its fleshy body,
thin and flattened from before backwards, becomes distinctly visible
only below the middle of the forearm. Above, it is enclosed in a limited
space, bounded in front by the common extensor of the digits, and
behind by the posterior ulnar; there these two muscles approach each
other so closely that from the point of view of external form they seem
to be nearly in contact.

The tendon, after receiving the small fasciculus from the common
extensor (Fig. 75, 16), as well as a fibrous band emanating from the
external surface of the carpus (Fig. 75, 17), is situated at the
external side of the tendon of the anterior extensor of the phalanges,
and is inserted into the anterior surface of the superior extremity of
the first phalanx.

This muscle extends the digit or digits into which it is inserted. It
also assists in the movement of extension of the hand as a whole.

=Posterior Ulnar= (_Extensor carpi ulnaris_) (Fig. 73, 11; Fig. 74, 17;
Fig. 75, 18).--Designated by veterinary anatomists as the _external
flexor of the metacarpus_,[27] or _external cubital_, this muscle is
situated in the posterior region of the external surface of the forearm,
behind the lateral extensor of the phalanges.

  [27] Certain authors give it the name of _ulnar extensor of the
       wrist_. It is true that in the human being this is its action;
       but in quadrupeds, owing to its insertion into the pisiform, it
       draws the hand into the position of flexion.

It arises from the epicondyle; its fleshy body, thick but flattened, is
directed vertically towards the carpus, and its tendon is inserted into
the external part of the superior extremity of the metacarpus, after
having given off a fibrous band, which takes its attachment on the
pisiform.

It is inserted, in the cat and the dog, into the superior extremity of
the fifth metacarpal; in the pig to the external metacarpal; in the ox
to the external side of the canon-bone; in the horse to the superior
extremity of the external rudimentary metacarpal.

This muscle flexes the hand on the forearm, and in animals in which the
radio-carpal articulation permits, by its formation, it inclines the
hand slightly outwards--that is, abducts it.

=Anconeus= (Fig. 72, 17; Fig. 73, 13).--We have already stated (p. 174)
that the anconeus is included with the triceps brachialis in zoological
anatomy, and that veterinary anatomists give it the name of _small
extensor of the forearm_.[28]

  [28] It is also called by some authors, the _small anconeus_.

In the dog it recalls, as to position, the human anconeus, but with this
difference--that, in the latter, the anconeus, triangular in outline,
has one of its angles turned outwards (the epicondyloid attachment) and
one of its sides turned towards the olecranon. Here it is entirely the
opposite. The anconeus, similarly triangular, is broader externally. At
this level it takes its origin from the external border of the humerus,
the epicondyle, and the external lateral ligament of the articulation of
the elbow; thence its fibres converge towards the external surface of
the olecranon, to be there inserted.

It is in relation, anteriorly and inferiorly, with the posterior ulnar
muscle. It is covered superiorly by the external head of the triceps. In
the cat the disposition of the anconeus is analogous. But in the other
quadrupeds with which we are here concerned it is completely covered by
the external head of the triceps. It really participates in the
formation of the triceps; and seeing that it takes origin from the
posterior surface of the humerus at the margin of the olecranon fossa
(Fig. 72), and proceeds thence towards the olecranon to be inserted, we
can understand why veterinary anatomists have connected its study with
that of the posterior muscular mass of the arm.

This muscle is an extensor of the forearm on the arm.

We proceed now to inquire what the deep muscles of the posterior region
of the human forearm become in quadrupeds: the long abductor of the
thumb, the short extensor of the thumb, the long extensor of the thumb,
the proper extensor of the index. We know that in every instance these
muscles, which are deeply seated at their origin, become superficial
afterwards.

In quadrupeds, on account of the position in which the forearm is
placed--viz., pronation--the corresponding muscles occupy the anterior
aspect of this region.

=Long Abductor of the Thumb= (_Extensor ossis metacarpi pollicis_) =and
Short Extensor of the Thumb= (_Extensor primi internodii pollicis_)
(Fig. 73, 14; Fig. 74, 19; Fig. 75, 20).--United one to the other in
man, blended in quadrupeds, they form in the latter the muscles to which
veterinary anatomists give the name of _oblique extensor of the
metacarpus_.

This muscle arises from the median portion of the skeleton of the
forearm. There it is covered by the common extensor of the digits and
that of the small digit (anterior extensor and lateral extensor of the
phalanges). Then, at the internal border of the first of these muscles,
it becomes superficial, passes downwards and inwards, crosses
superficially the anterior extensor of the metacarpus, reaches the
inferior extremity of the radius, and becomes lodged in the most
internal of the grooves situated on the anterior surface of this
extremity, passes on the internal side of the carpus, and is inserted
into the superior extremity of the most internal metacarpal--that is, to
the first metacarpal, or metacarpal of the thumb--in the dog and cat; to
the internal rudimentary metacarpal in the horse.

It is an extensor of the metacarpal into which it is inserted; but as,
if we recall the extreme examples given above, in the dog the first
metacarpal is not very mobile, and in the horse the internal rudimentary
metacarpal is absolutely fixed to the bone which it accompanies, it is
more exact to add that this muscle is principally an extensor of the
metacarpus as a whole.

And yet, in the cat and the dog, it is also able to adduct the first
metacarpal bone. It must be understood that this movement would be
abduction, if the hand could be placed in the position of complete
supination, as in the human species.

=Long Extensor of the Thumb= (_Extensor secundi internodii pollicis_)
=and Proper Extensor of the Index= (_Extensor indicis_).--These two
muscles are blended together by their fleshy bodies, so that the single
name of _proper extensor of the thumb and index_ is preferable. This
muscle is but of slight importance from our point of view, for it is
extremely atrophied, and so much the more as the number of the digits is
lessened.

It arises, as the preceding, from the skeleton of the forearm, and there
it is deeply placed. Below, towards the carpus, its tendinous part
becomes superficial, to end in the following manner:

In the carnivora, the tendon divides into two very slender parts, which
are inserted into the thumb and the index. In the pig, the tendon is
blended with that of the common extensor of the internal digits.
Finally, in the ox and the horse, it is sometimes regarded as being
blended with the common or anterior extensor of the phalanges. But to us
it appears more rational to say that it does not exist, which, moreover,
is explained by the digital simplification of the hand.


Internal and Posterior Region

=Pronator Teres= (Fig. 76, 8).--This muscle, as may easily be
understood, undergoes, as do the supinators, a degree of degeneration in
proportion to the loss of mobility of the radius on the ulna. In animals
in which the bones of the forearm are not fused it exists; in those, on
the other hand, in which this segment has become simply a supporting
column, it is not developed--at least, in a normal manner.

It is, consequently, found best marked in the dog and the cat.

Forming, as in man, the internal limit of the hollow of the elbow, the
pronator teres has a disposition analogous to that which characterizes
the corresponding muscle in the human species. It arises from the
epitrochlea (internal condyle), proceeds downwards and outwards, and is
inserted into the middle portion of the body of the radius.

It is into the hollow in front of the elbow, which this muscle
contributes to limit, that the biceps and the brachialis anticus dip.

In the pig and the ox it is atrophied.

In the horse it does not exist. We may, however, sometimes find it, but
in an abnormal form. We were able to demonstrate its presence in the
form of a fleshy tongue situated on the internal side of the elbow
(Fig. 78) in a horse which we dissected many years ago in the laboratory
of the School of Fine Arts. Moreover--and the fact seemed to us an
interesting one--the forearm to which the muscle belonged had an ulna of
relatively considerable development (Figs. 79 and 80).[29]

  [29] Édouard Cuyer, 'Abnormal Length of the Ulna and Presence of a
       Pronator Teres Muscle in a Horse' (_Bulletin de la Société
       d'Anthropologie_, Paris, 1887).

This muscle is a pronator.

=Flexor Carpi Radialis= (Fig. 76, 10; Fig. 77, 7).--Called by veterinary
anatomists _the internal flexor of the metacarpus_, this muscle, which
is found on the internal aspect of the forearm, is situated behind the
pronator teres when this muscle exists, whilst in the animals which are
deprived of the latter the flexor carpi radialis has in front of it the
internal border of the radius, which separates it from the anterior
extensor of the metacarpus.

It is necessary to add that the flexor carpi radialis is similarly
separated from the anterior extensor of the metacarpus by the internal
border of the radius in animals in which the pronator teres exists, but
then only in that part of the forearm which is situated below this
latter.

The flexor carpi radialis arises from the epitrochlea. Its fleshy body,
fusiform in shape, descends vertically, and terminates in a tendon on
the posterior surface of the bases of the second and third metacarpals
in the dog and the cat, on the metacarpal of the large internal digit in
the pig, on the internal side of the metacarpus in the ox, and on the
superior extremity of the internal rudimentary metacarpal in the horse.

We see clearly, in this latter, a superficial vein which, in the shape
of a strong cord, passes along the anterior border of the flexor carpi
radialis; it is the subcutaneous median or internal vein, which, forming
the continuation of the internal metacarpal vein, joins the venous
system of the arm, after having crossed obliquely the corresponding part
of the radius.

=Palmaris Longus.=--This muscle, which exists distinctly in some
animals, but whose absence is far from being rare in the human species,
is not developed as a distinct muscle in any of the domestic quadrupeds.

[Illustration: FIG. 76.--MYOLOGY OF THE DOG: LEFT ANTERIOR LIMB,
INTERNAL ASPECT.

1, Biceps; 2, long extensor of the forearm (supplementary or accessory
muscle of the great dorsal); 3, triceps, long head; 4, triceps, internal
head; 5, olecranon; 6, epitrochlea (internal condyle); 7, radial
extensors (anterior extensor of the metacarpus); 8, pronator teres; 9,
radius; 10, flexor carpi radialis (internal flexor of the metacarpus);
11, anterior ulnar (oblique flexor of the metacarpus); 12, superficial
flexor of the digits; 13, deep flexor of the digits; 14, flexor longus
pollicis (radial fasciculus of the deep flexor of the digits); 15,
pisiform bone.]

And yet some authors announce its presence in the dog, and describe it
as becoming detached, in the form of a cylindrical bundle, from the
anterior surface of the fleshy mass of the deep flexor of the digits
(see p. 196) to proceed then by a tendon which divides into two parts,
to terminate in the palm of the hand, where it blends with the tendons
of the superficial flexor, which are destined for the third and fourth
digits.

These authors give to this muscle the name of _palmaris longus_, and
attribute to it the action of flexing the hand.

=Anterior Ulnar= (_Flexor carpi ulnaris_) (Fig. 73, 16; Fig. 76, 11;
Fig. 77, 8).--Called by veterinary anatomists the _oblique flexor of the
metacarpus_, or _internal ulnar_, this muscle occupies the internal part
of the posterior aspect of the forearm in the ox and the horse, while in
the dog it occupies rather the external part.

This difference arises from the fact that in this latter, as in man, the
anterior ulnar is separated from the flexor carpi radialis by an
interval in which we see, on the internal aspect of the forearm, just at
the level of the elbow, the flexors of the digits. This interval is so
much the wider as there is no palmaris muscle to subdivide its extent
(Fig. 81). In the horse, the interval in question does not exist. In
this animal, indeed, the anterior ulnar is in contact with the radial
flexor, so that this muscle can occupy only a region belonging rather to
the internal surface of the forearm (Fig. 82).

In the dog the anterior ulnar is in contact with the posterior ulnar.
This relation recalls that which is found in man, where the two muscles
are merely separated by the crest of the ulna (Fig. 81). But in the
horse, in which the anterior ulnar has, so to speak, slid towards the
internal aspect, this muscle is separated above from the posterior
ulnar, and it is in the interval separating these two muscles that we
are able to perceive, but this time at the back of the forearm, the
muscular mass of the flexors of the digits (Fig. 82).

[Illustration: FIG. 77.--MYOLOGY OF THE HORSE: ANTERIOR LIMB, LEFT SIDE,
INTERNAL ASPECT.

1, Long extensor of the forearm (supplementary or accessory muscle of
the latissimus dorsi); 2, radialis muscles (anterior extensor of the
metacarpus); 3, tendons of extensor ossis metacarpi pollicis extensor
primi internodii pollicis united (oblique extensor of the metacarpus);
4, tendon of extensor communis digitorum (anterior extensor of the
phalanges); 5, strengthening band from the suspensory ligament of the
fetlock; 6, internal surface of the radius; 7, flexor carpi radialis
(internal flexor of the metacarpus); 8, anterior ulnar (oblique flexor
of the metacarpus); 9, pisiform bone; 10, 10, tendon of the superficial
flexor of the digits (superficial flexor of the phalanges); 11, 11,
tendon of the deep flexor of the digits (deep flexor of the phalanges);
12, sesamoid prominence; 13, suspensory ligament of the fetlock; 14,
internal rudimentary metacarpal.]

The anterior ulnar arises above from the epitrochlea and the olecranon;
thence it is directed towards the carpus, to be inserted into the
pisiform bone. It proceeds therefore from the inner side of the elbow to
the outer side of the upper part of the hand; it consequently crosses
the posterior surface of the forearm obliquely. This is why, as we have
pointed out above, it receives the name of the oblique flexor of the
metacarpus.

It is not unprofitable to recall in this connection that there is an
internal flexor of the metacarpus, which is the flexor carpi radialis;
and an external flexor of the metacarpus, which is the posterior ulnar
(in human anatomy, extensor carpi ulnaris). It is between these two
muscles that we find the oblique flexor--the anterior ulnar which we
have just been studying.

This muscle flexes the hand on the forearm.

=Superficial Flexor of the Digits= (_Flexor digitorum sublimis_) (Fig.
76, 12; Fig. 77, 10, 10).--This muscle arises from the epitrochlea;
thence it passes towards the hand, becomes tendinous, passes in a groove
on the posterior aspect of the carpus, and terminates on the palmar
surface of the phalanges in furnishing a number of tendons proportioned
to the digital division of the hand. Whatever the number, to which we
will again refer, each tendon is attached to the second phalanx, after
bifurcating at the level of the first, so as to form a sort of ring,
destined to give passage to the corresponding tendon of the deep flexor.
This ring and this passage have gained for the muscle the name of
_perforated flexor_.

In the dog and the cat the principal tendon is divided into four parts,
which go to the four last digits.

In the ox it is divided into two parts only; as, moreover, in the pig,
whose superficial flexor is destined for the two large digits only, the
lateral digits receiving no part of it.

Finally, in the horse the tendon is single.

We have previously pointed out that in the carnivora this muscle is
visible on the internal and posterior aspects of the forearm, in the
interval which is limited in front by the flexor carpi radialis and
behind and outside by the anterior ulnar.

Certain details are still to be added to the description of this
muscle. We will enter on an analysis of them after we have given some
indications relative to the following muscle:

=Deep Flexor of the Digits= (_Flexor digitorum profundus_) (Fig. 75, 21,
22; Fig. 76, 12; Fig. 77, 11, 11).--This muscle is covered by the
superficial flexor. It arises from the epitrochlea, from the radius, and
from the ulna, either from the olecranon process--as in the ox, pig, and
horse--or from almost the whole extent of the shaft of the same bone, as
in the cat and dog.

[Illustration: FIG. 78.--LEFT ANTERIOR LIMB OF THE HORSE: INTERNAL
ASPECT.

1, Internal flexor of the metacarpus or great palmar; 2, inferior part
of the biceps; 3, inferior part of the brachialis anticus; 4, internal
lateral ligament of the elbow; 5, pronato teres muscle.]

The radial fasciculus represents in the domestic quadrupeds the long
proper flexor muscle of the thumb in man. For this reason we shall
describe the muscle afresh in the following paragraph:

The fleshy bundles of which we have just spoken terminate in a tendon
which afterwards divides into slips, the number of which is in
proportion to the digital division of the hand. These slips then pass
through the slit or _buttonhole_ in the tendon of the superficial
flexor, and proceed to terminate on the third phalanx; hence the name of
_perforating_, which is also given to the deep flexor of the digits.

In the dog and the cat the tendon is divided into five portions, each of
which proceeds to one of the digits. The internal tendon, which is
destined for the thumb, terminates on the second phalanx of this digit.

In the pig the tendon divides into four tendons destined for the four
digits.

In the ox there are but two tendons.

In the horse the tendon is single.

As their names indicate, these muscles, both superficial and deep, flex
the digits. In addition to this, they flex the hand on the forearm.

We mentioned above that certain details relative to the superficial
flexor must be analyzed in a special way. We now add that this should
also be done with regard to the deep flexor. The point in question is
the arrangement which the tendons of these muscles present at the level
of the palmar region of the hand.

It is easy, in the case of the dog or the cat, to picture to one's self
this arrangement, especially if we recollect that which exists in the
human species. The tendons of the flexors are placed on a kind of
muscular bed formed by the union of the muscles of the region, but,
moreover, from the point of view of external form, these tendons are not
of very great importance.

But in the ox and the horse it is quite otherwise. From the
simplification of the skeleton of the hand, and the reduction of the
number of movements which the bones that form it are able to execute,
there naturally results a diminution of its muscular apparatus. Apart
from the existence of muscular vestiges of but little importance, we can
say that, in reality, the hand does not possess any muscles. On its
palmar aspect are found only the tendons of the flexors of the digits,
and as these tendons are large, and the hand long, they give origin to
external forms which it is necessary to examine.

[Illustration: FIG. 79.--LEFT ANTERIOR LIMB OF THE HORSE: EXTERNAL
ASPECT.

1, Ulna of abnormal length.]

[Illustration: FIG. 80.--LEFT ANTERIOR LIMB OF THE HORSE: EXTERNAL
ASPECT.

1, Normal ulna.]

In the horse, which we take as a type, the tendons of the flexors, after
being retained in position at the carpus by a fibrous band, the _carpal
sheath_, which recalls the anterior annular ligament of the human
carpus, and having passed this region, descend vertically, remaining
separated from the posterior surface of the metacarpus, so that the skin
sinks slightly on the lateral parts in front of the thick cord which
these tendons form. This cord is known by the name of _tendon_.

The flexors then reach the fetlock, and occupy the groove formed by the
peculiar arrangement of the two large sesamoid bones. They are retained
in position at this level by a fibrous structure, which forms the
metacarpo-phalangeal sheath. They then reach the phalanges, being
directed obliquely downwards and forwards, as, moreover, the latter are
also inclined. Then the tendon of the superficial flexor divides into
two slips, which are inserted into the second phalanx, between which
slips passes the tendon of the deep flexor, which in its turn goes to be
inserted, in the form of an expansion, into the semilunar crest, by
which the inferior surface of the third phalanx is divided into two
parts.[30]

  [30] See, as regards this crest, in the paragraph relative to the hoof
       of the solipeds, the figures which represent the third phalanx,
       viewed on its inferior surface (Figs. 101 and 102, p. 258).

The part which these tendons play is of great importance in the large
quadrupeds.

These tendons, in fact, in addition to the action determined by the
contraction of the fleshy fibres to which they succeed, maintain the
angle formed by the canon-bone and the phalangeal portion of the hand,
and prevent its effacement under the weight of the body during the time
of standing. Their strong development, and the position they occupy,
make this understood, without it being necessary to insist on it
further.

We mentioned above that the 'tendon' descends vertically from the carpus
towards the fetlocks. This is as it should be. But, in some horses, it
is oblique downwards and backwards, so that the canon, instead of being
of equal depth from before backwards in its whole length, is a little
narrower in its upper part.

This results from the fact that the tendons of the flexors, too firmly
bound by the carpal sheath, gradually separate as they pass from the
metacarpus, going to join the fetlock; hence the obliquity pointed out
above. This abnormality producing a deleterious result, in the sense
that the tendinous apparatus acts with less strength as an organ of
support, it constitutes a defect of conformation which is expressed by
saying that the tendon has 'failed.'

=Long Proper Flexor of the Thumb= (_Flexor longus pollicis_) (Fig. 76,
14).--As we have already pointed out, this muscle is represented in
quadrupeds by the radial bundle of the deep flexor of the digits, so
that the two muscles are in reality blended the one to the other. This
union is sometimes found, but only as an abnormality, in the human
species. We have met some examples of this in the course of our
dissections.

=Pronator Quadratus.=--This muscle conforms to the general law which we
have already pointed out in connection with those which have for their
action the rotation of the radius around the ulna. We remember, indeed,
that when the bones of the forearm are fused with one another, the
muscles which are destined to produce a mobility which has then become
impossible disappear at the same blow.

[Illustration: FIG. 81.--DIAGRAM OF THE POSTERIOR PART OF A TRANSVERSE
SECTION PASSING THROUGH THE MIDDLE OF THE LEFT FORE-LIMB OF THE DOG:
SURFACE OF THE INFERIOR SEGMENT OF THE SECTION.

1, Radius; 2, ulna; 3, posterior ulnar; 4, anterior ulnar; 5, great
palmar (_flexor carpi radialis_); 6, flexors of the digits.]

[Illustration: FIG. 82.--DIAGRAM OF A HORIZONTAL SECTION OF THE MIDDLE
OF THE FOREARM OF THE LEFT LEG OF THE HORSE: SURFACE OF THE INFERIOR
SEGMENT OF THE SECTION.

1, Radius; 2, ulna; 3, posterior ulnar; 4, anterior ulnar; 5, great
palmar (_flexor carpi radialis_); 6, flexors of the digits.]

For this cause we do not find the square pronator in either the ox or
the horse, but can demonstrate its presence in the dog and the cat.

It is very deeply situated. This is why, and also on account of the plan
which we have traced for ourselves, we will simply say that it is
situated on the postero-internal aspect of the skeleton of the forearm,
and that it extends from the ulna to the radius.

It seems to us, however, sufficiently interesting to add that, instead
of occupying, as in the human species, the inferior fourth of the two
bones, it extends, particularly in the dog, over their whole length,
with the exception of their superior and inferior extremities.


Muscles of the Hand

We will first recall that, in man, the palm of the hand is divided into
three regions: a median palmar region, which is occupied by the tendons
of the flexors of the digits, the lumbricales, and, deeply, by the
interosseous muscles; an external region, or thenar eminence, formed by
the muscles destined for the movements of the thumb; an internal region,
or hypothenar eminence, which contains the muscles proper to the small
digit and the palmar cutaneous muscle.

These muscles are found, more or less developed, in the dog and the cat.

In the ox and the horse we meet with no vestige of the muscles of the
thenar or hypothenar eminences. Nevertheless, in these animals we find
the muscles which belong to the central region of the palm. We refer to
the lumbricales and the interosseous.

Although this fact has no relation to the object of our study, it
appears to us interesting to announce that there are traces of the
lumbricales found in the solipeds. These muscles are represented by two
fleshy bundles, situated one on each side of the tendon of the deep
flexor, above the ring of the tendon of the superficial flexor. These
small muscles are continued as slender tendons, which become lost in the
fibrous tissue of the _spur_, which is the horny process situated at the
posterior part of the fetlock, and which is covered by the hairs, more
or less abundant, which constitute the _wisp_.

As for the interosseous muscles, they are represented by the _suspensory
ligament of the fetlock_, and by two other small muscles, tendinous
throughout, which are situated between the principal metacarpal and the
rudimentary ones.

The suspensory ligament of the fetlock is considered an interosseous
muscle, on account of the red fleshy striations which it contains, and
from certain relations which it forms with the tendon of the common
extensor of the digits or anterior extensor of the phalanges. This
ligament (Fig. 75, 26; Fig. 77, 13), which plays an important part in
the standing position as a support of the foot, is a fibrous band
situated between the tendons of the flexors of the digits and the
principal metacarpal. It arises above, from the second row of the
carpals, descends towards the fetlock, where it divides into two
branches, which are inserted into the large sesamoid bones. At the same
level, this ligament gives off two fibrous bands which, passing
downwards and forwards, join the tendon of the anterior extensor of the
phalanges, blending with it, after having each crossed one of the
lateral aspects of the pastern. We have already referred to these bands
(p. 183).

It is with these latter that are blended the long and slender tendons
which form in a great measure the two other interosseous muscles
previously described.

A ligament of the same kind is found in the ox (Fig. 74, 23).


MUSCLES OF THE POSTERIOR LIMBS


Muscles of the Pelvis

The muscles which specially interest us in this region, because of their
superficial position, are the gluteus maximus and the gluteus medius. As
for the gluteus minimus, it is deeply situated, and more or less sharply
marked off from the second of the preceding muscles.

Inasmuch as the gluteus medius is more simple in arrangement than the
maximus, and will aid us in arranging our ideas in connection with the
latter, it is with the study of it that we will commence.

=Gluteus Medius= (Fig. 68, 29; Fig. 69, 26; Fig. 70, 35).--This muscle,
as in man, occupies the external iliac fossa. But this latter being
directed differently in the digitigrades and the ungulates, as we have
pointed out in the section on osteology (see pp. 91 and 99), the muscle
in question has consequently not the same direction in the two groups of
animals, being turned outwards in the first, and upwards in the second.

It is the thickest of the glutei, and gives to the region which it
occupies a rounded form.

From the iliac fossa from which it arises the fleshy fibres are directed
towards the femur, to be inserted into the great trochanter. It is
covered by an aponeurosis, and in part by the great gluteal. It
completely covers the small gluteal, which veterinary anatomists
designate by the name of the _deep gluteal_.

In the carnivora it does not pass in front of the iliac crest, but, in
the ox, and more particularly in the horse, it is prolonged anteriorly,
and thus covers, to a certain extent, the muscles of the common mass.

When it contracts, taking its fixed point at the pelvis, the gluteus
medius extends the thigh, which it is also able to abduct. If, on the
other hand, its fixed point is on the femur, it acts on the trunk, which
it raises, producing oscillating movements of the pelvis. It contributes
in this way to the action of rearing. We also see it distinctly appear
by the prominence which it produces in the dog, which, according to the
time-honoured phrase, _fait le beau_.

=Gluteus Maximus= (Fig. 68, 28; Fig. 69, 25; Fig. 70, 33, 34).--The
great gluteal muscle, further designated in veterinary anatomy the
_superficial gluteal_, is proportionately less developed in quadrupeds
than in man. Indeed, in the latter, where it is of very great thickness,
its volume is due to the important function which it fulfils in
maintaining the biped attitude.

In quadrupeds it contributes to form the superficial part of the crupper
and the external surface of the thigh. It is divided into two parts: one
anterior, the other posterior.

With regard to this latter, it will be necessary to indicate how it has
been sometimes regarded, and to what portion of the muscular system in
man it corresponds. But we believe that it is better to see beforehand,
without any preconceived idea, how these two parts are arranged.

In the dog, the anterior portion of the gluteus maximus arises from the
sacrum, while some fibres situated further forward arise from the
surface of the gluteus medius, near the iliac spine, and from the tensor
of the fascia lata with which these fibres are blended. The posterior
portion, united to the preceding--that is to say, to those of its fibres
which arise from the sacrum--takes its origin from the first coccygeal
vertebra. These two portions are directed towards the femur, to be
inserted into the great trochanter, and to the external branch of the
superior bifurcation of the linea aspera.

In the cat, the posterior bundle is less definitely blended with the
anterior. By a long and slender tendon which, behind, turns around the
great trochanter, and passes along the surface of the fascia lata, it
proceeds to join the knee-cap.

In the pig, the posterior portion is much more developed.

In the horse, the anterior portion arises from the internal iliac spine
(posterior in man), from the external iliac spine (anterior in man),
and, between these two osseous points, from the aponeurosis, which
covers the gluteus medius. Between these two origins the muscle is
deeply grooved, so that the tendency is to divide into two portions,
each of which is directed towards one of the iliac angles. In this
groove the gluteus medius is to be seen.

The fleshy bundles converge, and are directed towards the external
aspect of the femur, to be inserted into the osseous prominence known as
the third trochanter, after passing beneath the fleshy fibres of the
posterior portion. The latter, which is more considerable than the
preceding portion, arises above from the sacral crest, from the
aponeurosis which envelops the coccygeal muscles, from the sacro-sciatic
ligament, and from the tuberosity of the ischium. From this origin it
passes downwards, expands, then, describing a curve with the convexity
behind, it becomes narrowed, and proceeds to be inserted by a deep
fasciculus into the third trochanter, to the fascia lata, and, lastly,
to the knee-cap by the inferior part of its tendon.

Above, its posterior border is covered by the semi-tendinosus;
interiorly, the same border is in relation with the biceps femoris.

In the ox, the two parts of the great gluteal muscle are blended
together.

The long and broad fleshy band which they form arises in a manner
corresponding to that which we have just indicated in connection with
the horse, except that it has no attachment to the femur. The fascia
lata adheres strongly to its anterior border for a considerable length.
The form of the superior border of the great gluteal muscle of this
animal differs from that of the analogous portion in the horse. This
difference results from the peculiar aspect which the corresponding
region of the pelvis presents, and from the fact that, in the ox, as the
semi-tendinosus does not cover the portion of the great gluteal which
arises from the tuberosity of the ischium, the attachments of this
muscle to the sacro-sciatic ligament are uncovered.

Its descending portion, as a whole, has a rectilinear form, and does not
form a curve such as we indicated in the case of the horse.

The anterior portion of the great gluteal flexes the thigh. As regards
the posterior portion, it extends the thigh, and abducts it.

The action of this latter portion is particularly interesting as regards
the horse, because of the great development of the muscular mass which
this region presents in this animal. If the muscle takes its fixed point
above, it acts, in the extension of the thigh during walking, by
projecting the trunk forward during the whole time that the hind-limb to
which it belongs is in contact with the ground. If, on the contrary, it
takes its fixed point below, it makes the pelvis describe a see-saw
movement, upwards and backwards, on the coxo-femoral articulation, and
so contributes to the action of rearing.

Now that we have a knowledge of the disposition of the great gluteal
muscle, the moment has come to inquire what is the signification of its
posterior portion. The action of the anterior part being clearly
comparable to the human great gluteal, there can be no doubt as regards
the homology of this portion, so we will not insist on it further.

Of the posterior portion it is wholly different, for it is the homologue
of a fleshy bundle annexed to the great gluteal of man, but which is not
developed except as an abnormality.

Indeed, we sometimes find, placed along the inferior border of the great
gluteal, a fleshy fasciculus, separated from this muscle by a slight
interspace. This fasciculus, long and narrow, takes origin from the
summit of the sacrum, or the coccyx, and goes to partake of the femoral
insertions of the muscle which it accompanies. We further note a muscle
of the same kind, and presenting the same aspect, which comes from the
tuberosity of the ischium. Notwithstanding the difference which exists,
it is this abnormal fasciculus of man which in the quadrupeds here
studied is considered as constituting the posterior portion of the great
gluteal.

Bourgelat, considering this posterior portion as belonging to the biceps
cruris, to which, it is true, it adheres, forms of them a muscle which
he designates under the name of the _long vastus_. The anterior
fasciculus of this long vastus is none other than the posterior portion
of the great gluteal which we have just been studying.


Muscles of the Thigh

These muscles are divided into three regions: posterior, anterior, and
internal.

In a corresponding manner to that which we described in connection with
the arm, the thigh is applied to the side of the trunk, and is free,
more or less, only at the level of the inferior part.

Further, by reason of this shortening of the femur, the great gluteal
muscle, which is elongated in the ox and the horse, for example,
occupies in part the region corresponding to that which in man is
occupied by the muscles of the thigh, which here are reduced in length.
In other words, they are not superposed, as in the human species, but
juxtaposed. This is what we will verify further on.

The thigh, as a whole, is flattened from without inwards, its transverse
diameter being less in extent than its antero-posterior. Its external
surface is slightly rounded; that is, of course, in quadrupeds with
sufficiently well-developed muscles. Its internal surface is known as
the _flat of the thigh_.


Muscles of the Posterior Region

It is not unprofitable to recall to mind what muscles form the
superficial layer of this region in the human being. They are the biceps
cruris, semi-tendinosus, and semi-membranosus. We now proceed to
discover their analogues in quadrupeds.

=Biceps Cruris= (Fig. 68, 30; Fig. 69, 27; Fig. 70, 36).--It is this
which, according to Bourgelat, forms the central and posterior portions
of the long vastus muscle which we have mentioned above.

We know that the biceps of man is so named from the two portions which
form its upper part. In domestic quadrupeds, and also in the majority of
the mammals, this muscle is reduced to a single portion, that which
comes from the pelvis. It is therefore the portion which arises from the
femur which does not exist. This condition is sometimes found as an
abnormality in the human species.

The biceps arises from the tuberosity of the ischium; hence it is
directed, widening as it goes, towards the leg, where it terminates by
an aponeurosis which blends with the fascia lata and the aponeurosis of
the leg, and then proceeds to be attached to the anterior border or
crest of the tibia. By its inferior portion it limits externally the
posterior region of the knee--the popliteal space.

A fibrous intersection traverses the biceps in its whole length, with
the result that the muscle looks as if formed of two portions, one of
which is situated in front of the other.

In the dog and the cat it also arises from the sacro-sciatic ligament.
At this level its contour is distinguishable from that which corresponds
to the gluteal muscles, so that we there find two prominences one above
the other. The superior is formed by the gluteal muscles; the inferior
corresponds to the tuberosity of the ischium. The two prominences are
separated by a depression, from which the biceps emerges. We draw
attention to this form, the character of which is so expressive of
energy in the carnivora.

In these animals the biceps is inserted, by its anterior fibres, into
the articulation of the knee, while in the rest of its extent it covers
in great measure by its aponeurosis the external aspect of the leg.

In the pig, the biceps is but slightly marked off from the posterior
part of the great gluteal. In the ox, the division between these two
muscles is a little more distinct.

In the horse, the sciatic origin of the biceps is covered by the
semi-tendinosus, so that it only becomes free lower down, to appear in
the space limited behind by the semi-tendinosus, and in front by the
posterior part of the gluteus maximus.

When the biceps contracts, taking its fixed point from above, it flexes
the leg and helps to extend the thigh. If, on the other hand, it takes
its fixed point from below, it lowers the ischium, makes the pelvis
undergo a see-saw movement, and acts thus in the movement of rearing. It
is sometimes called, on account of one of its actions, and the position
which it occupies, the 'external flexor, or peroneal muscle of the leg.'

=Semi-tendinosus= (Fig. 68, 31; Fig. 70, 37; Fig. 87, 1; Fig. 88, 1;
Fig. 89, 28).--This muscle forms the contour of the thigh posteriorly,
so that when the latter is viewed from the side, it is the
semi-tendinosus above all that forms the outline. But, as we shall soon
see, it is in this case more distinct above than below, because of the
deviation which it undergoes in order to occupy by its inferior part the
internal side of the leg.

In the dog, the cat, and the ox, the semi-tendinosus arises from the
tuberosity of the ischium only, as in the human species. In the pig, it
also takes origin higher up from the sacro-sciatic ligament and the
coccygeal aponeurosis. In the horse, it extends still further, for it is
also attached to the crest of the sacrum.

The indication of these origins is of importance from the point of view
of external form, and to convince ourselves of this it is sufficient to
compare, in the ox and the horse, the region of the pelvis situated
below the root of the tail. In the ox, whose semi-tendinosus arises from
the tuberosity of the ischium only, this region is depressed, and the
cavity which is formed at this level is limited behind by the
tuberosity, which we know is very thick and prominent above. This causes
the superior part of the crupper to be less oblique than in the horse.
This characteristic is more especially marked in the cow, the bull
having this region of a more rounded form.

In the horse, on account of the semi-tendinosus ascending to the coccyx,
and even to the sacrum, the depression in question does not exist, and
the presence of the tuberosity of the ischium is only slightly revealed.

Descending from the origin indicated above, and inclining more and more
inwards, the semi-tendinosus proceeds to blend with the aponeurosis of
the leg, to be inserted into the anterior border of the tibia, after
crossing over the internal surface of the latter. It forms the internal
boundary of the popliteal space.

When this muscle contracts, taking its fixed point at the pelvis, it
flexes the leg. If, on the other hand, it takes its fixed point at the
tibia, it makes the pelvis describe a see-saw movement, and acts
accordingly in the movement of rearing.

It is sometimes named the 'internal or tibial flexor of the leg,' in
opposition to the crural biceps, which, as stated above, is then the
external flexor of the same region.

=Semi-membranosus= (Fig. 68, 32; Fig. 87, 2; Fig. 88, 2).--This muscle,
situated on the inner side of the semi-tendinosus, can be seen only when
the thigh is regarded on its posterior aspect.

It is only by reason of the homology of situation with the corresponding
muscle in man that we give the name under which we are studying it;
indeed, its structure is different, for it does not present the long,
broad, aponeurotic tendon which, in its superior part, characterizes
this muscle in the human species.

It arises above from the inferior surface of the ischium, and from the
tuberosity of the same bone. In the pig, and especially in the horse, it
passes further upwards, to arise from the aponeurosis of the coccygeal
muscles. So that if we compare it with that of the ox, which does not
extend beyond the ischium, we find that it is associated with the
semi-tendinosus in determining the difference of aspect to which we have
already called attention in connection with the region of the pelvis
situated below the root of the tail.

The semi-membranosus is then directed downwards and forwards, to take
its place on the internal surface of the thigh, where it is partly
covered by the gracilis muscle. It is inserted in the following manner:

In the dog and the cat it is divided into two parts, anterior and
posterior. The first, the more developed, is attached to the internal
surface of the inferior extremity of the femur; the second to the
internal tuberosity of the tibia.

The same arrangement occurs in the ox.

In the horse it is inserted into the internal surface of the internal
condyle of the femur.

The semi-membranosus is an extensor of the thigh when it takes its fixed
point at the pelvis; it is also an adductor of the lower limb. If it
takes its fixed point below it assists in the action of rearing.

It is now necessary for us, especially as regards the horse, to add some
indications relative to the exterior forms of the region constituted by
the semi-membranosus and semi-tendinosus. These two muscles form, by
their union, a surface contour, slightly projecting and of elongated
form, which occupies the posterior border of the thigh, the contour
corresponding to the region known as the _buttock_, in spite of the
fact that none of the gluteal muscles take any part in the structure of
this region. But the appearances, to a certain extent, justify the
preservation of this name. Indeed, because of the groove which separates
the gluteal region of one side from that of the opposite side, and from
the position of the anal orifice in the superior part of this groove, we
may admit the name which, in hippology, has been given to this part of
the thigh.

In addition to the reasons just given, and which are justified
especially by the position occupied by the muscular mass formed by the
union of the two muscles, there is another which, this time, has a
relation to a certain detail of form. In the superior part of the
convexity, which the gluteal region describes in the greater part of its
extent, there is found a more salient point, greatly accentuated in lean
animals, due to the presence of the tuberosity of the ischium; it is the
_point_ or _angle of the buttock_. At this level, and near the median
line, the semi-membranosus, not aponeurotic, but fleshy, and even
thicker there than anywhere else, sometimes produces a sharply localized
prominence. And as this prominence is situated on the outer side of the
anal orifice, the resemblance to a small 'buttock' is still more marked.

In lean horses a deep groove separates the mass formed by the
semi-membranosus and semi-tendinosus from that of the other muscles of
the thigh situated more in front; this groove is known by a name which
in this case is remarkably expressive--that of the 'line of poverty.'

If we examine the gluteal region as a whole by looking at the thigh from
the side, we plainly see the graceful curve produced by the general
convexity above indicated. We return to this point, in order to add
that, in its lower part, this curve alters its character; that is to
say, it is replaced by a slight concavity. This, which is designated
under the name of _the fold of the buttock_, is situated close to the
level of articulation of the leg with the thigh-bone.


Muscles of the Anterior Region

First we recall that in man the anterior muscles of the thigh are: the
triceps cruris, the tensor of the fascia lata, and the sartorius.

=Triceps Cruris= (Fig. 8, 36; Fig. 69, 31; Fig. 70, 41; Fig. 84, 2; Fig.
87, 3; Fig. 88, 3).--This muscle, which occupies the greater part of the
space between the pelvis and the anterior aspect of the femur, consists
of three parts: an external, or vastus externus; an internal, or vastus
internus; and a median or long portion, or rectus femoris. This division
accordingly recalls that which characterizes the human triceps cruris.
Furthermore, as in the case of the latter, the vastus externus and the
vastus internus take their origin from the shaft of the femur, while the
long portion arises from the pelvis. The _vastus externus_ arises from
the external lip of the linea aspera of the femur (or from the external
border of the posterior surface of this bone in the ox and the horse, in
which the linea aspera, considerably widened, especially in the latter,
forms a surface), and from the external surface of the shaft of the
femur. From this origin its fibres pass downwards and forwards, to be
inserted into the tendon of the long portion of the muscle and into the
patella.

In the dog and the cat the vastus externus is the most voluminous of the
three portions which constitute the triceps muscle. It is covered by the
fascia lata; but notwithstanding this, its presence is revealed by a
prominence which occupies the external surface of the thigh, and
surmounts, in the region of the knee, the more slightly developed one
which is produced by the knee-cap.

The _vastus internus_, situated on the inner surface of the thigh, takes
its origin from the corresponding surface of the femur, and proceeds
towards the patella.

The rectus femoris arises from the iliac bone, above the cotyloid
cavity; its fleshy body, which is fusiform, and situated in front of and
between the two vasti muscles, is directed towards the patella, into
which it is inserted by a tendon, which receives the other two
portions.

It is covered in front by the tensor of the fascia lata, and contributes
with the vastus externus to form the upper prominence of the knee.

The ligamentous fibres, which, as in man, unite the knee-cap to the
tibia, transmit to this latter the action determined by the contraction
of the triceps. This muscle is an extensor of the leg. Furthermore, the
rectus femoris, or long portion, acts as a flexor of the thigh.

=Tensor Fascia Lata= (Fig. 68, 34, 36; Fig. 69, 30, 31; Fig. 70,
40).--This muscle, generally larger in quadrupeds than in man, is flat
and triangular, and occupies the superior and anterior part of the
thigh.

It arises from the anterior iliac spine (inferior in carnivora, external
in the ox and the horse); it is prolonged downwards by an aponeurosis
(fascia lata) which occupies the external aspect of the thigh, proceeds
to be inserted into the patella and blend with the aponeurosis of the
biceps muscle.

It covers the rectus and vastus externus portions of the triceps cruris;
it is also in relation with the gluteal muscles.

The tensor of the fascia lata flexes the thigh, and serves to raise the
lower limb as a whole.

=Sartorius= (Fig. 68, 35; Fig. 87, 4, 5; Fig. 88, 5).--This muscle, long
and flattened, is called by veterinarians _the long adductor of the
leg_.

Before beginning the study of its position in quadrupeds, it is
necessary to remember that in man, where the thigh has a form almost
conical, the sartorius commences on the anterior face of this latter,
and is directed downwards and inwards to reach the internal surface of
the knee.

But now let us suppose the thigh flattened from without inwards; there
will evidently result from this a change in situation with regard to the
muscle in question. In fact, when this supposition is admitted, it is
easy to imagine that in a great part of the extent in which the
sartorius is normally anterior it will become internal. This is why,
these conditions being realized in quadrupeds, we shall find that, in
some of them, the sartorius is situated on the aspect of the thigh which
is turned to the side of the trunk.

In the dog and the cat it arises from the anterior iliac spine, and from
the half of the border of the bone situated immediately below it; but
the fibres from this second origin being hidden by the tensor of the
fascia lata, on the inner side of which they are situated, viewing the
external surface of the thigh, the muscle seems to arise from the iliac
spine only.

The sartorius in these animals is divided into two parts, which, in
general, are placed in contact. One of these fasciculi is anterior; the
other is situated further back. The first is visible on the anterior
border of the thigh, in front of the tensor of the fascia lata, but
below it inclines inwards; in its superior part also, a small extent of
the internal surface is occupied by it. The second, which, as we have
said, is situated further back, belongs wholly to the inner surface of
the thigh; it is this portion which arises from the inferior border of
the ilium (this is the homologue of the anterior border of the human
iliac bone).

The two fasciculi then pass towards the knee, being in relation with the
rectus and the vastus internus of the triceps. The anterior fasciculus
is inserted into the patella. The posterior unites with the tendons of
the gracilis (see below) and semi-tendinosus, and then proceeds to be
inserted into the superior part of the internal surface of the tibia.

On account of their different insertions these two parts receive the
names of _the patellar sartorius_ and _tibial sartorius_ respectively.

In the ox and the horse the sartorius is still more definitely situated
on the internal surface of the thigh. Consisting of a single fasciculus,
representing the tibial sartorius of the cat and the dog, it arises in
the abdominal cavity from the fascia covering the iliac muscle, then
passes under the crural arch, and terminates, by an aponeurosis which
blends with that of the gracilis, on the inner fibres of the patellar
ligament. In short, the sartorius is of interest to us in the carnivora
only, and especially on account of its anterior or patellar fasciculus.

It is an adductor of the leg and a flexor of the thigh.


Muscles of the Internal Region

The ilio-psoas pectineus and the adductors which we study in man, in
connection with the internal aspect of the thigh, offer little of
interest from the point of view of external form in quadrupeds; it is
for this reason that we will disregard them.

The gracilis alone merits description.

=Gracilis= (Fig. 87, 9; Fig. 88, 6).--Designated in veterinary anatomy
under the name of _the short adductor of the leg_, this muscle, expanded
in width, occupies the greater part of the internal surface of the
thigh, _or flat of the thigh_, as this region is also called. Let us
imagine, in man, the internal surface of the thigh broader, and the
internal rectus more expanded, and we shall have an idea of the same
muscle as it exists in quadrupeds.

The gracilis arises from the ischio-pubic symphysis and from the
neighbouring regions; thence it is directed towards the leg to be
inserted into the superior part of the internal surface of the tibia,
after being united to the tendons of the sartorius and semi-tendinosus.
We find, accordingly, at this level, an arrangement which recalls the
general appearance of what in man receives the name of _the goose's
foot_ (_pes anserinus_).

It is between this muscle and the sartorius, at the superior part of the
internal surface of the thigh, in the region which recalls the triangle
of Scarpa, that we are able, especially in the cat and the dog, to see
the adductor muscles of the thigh. We also partly see there, in these
animals, the vastus internus and the rectus of the triceps (see Fig.
87). The gracilis is an adductor of the thigh.


Muscles of the Leg

We will divide the leg into three regions: anterior, external, and
posterior. With regard to the internal region, there are no muscles
which belong exclusively to it; for it is in great measure formed by the
internal surface of the tibia, which, as in man, is subcutaneous.


Muscles of the Anterior Region

We first note that in the human species the tibialis anticus, extensor
proprius pollicis, extensor longus digitorum and the peroneous tertius
or anticus, form the subcutaneous layer of this region. We now proceed
to study these muscles in quadrupeds.

[Illustration: FIG. 83.--MYOLOGY OF THE HORSE: THE ANTERIOR TIBIAL
MUSCLE (FLEXOR OF THE METATARSUS), LEFT LEG, ANTERIOR VIEW.

1, Femoral trochlea; 2, tibia; 3, tendinous portion of the tibialis
anticus; 4, cuboid branch of same; 5, 5, its metatarsal branch; 6,
fleshy portion; 7, cuneiform branch of its tendon; 8, metatarsal branch
of the same tendon; 9, extensor longus digitorum (anterior extensor of
the phalanges turned outwards); 10, peroneus brevis (lateral extensor of
the phalanges).]

=Tibialis Anticus= (Fig. 83; Fig. 84, 6; Fig. 85, 4; Fig. 87, 10; Fig.
88, 10, 11).--It is further named by veterinarians the _flexor of the
metatarsus_.

In the dog and the cat this muscle, which is rather large, arises from
the external tuberosity of the tibia and from the crest of this bone. In
its superior part it is flat, but lower down it is thick and produces a
prominence in front of the tibia. Finally, it becomes tendinous, and
passes towards the tarsus; thence it is directed towards the inner side
of the metatarsus, and is inserted into the great-toe, this latter being
sometimes well developed, but also often merely represented by a small
bony nodule on which the muscle is then fixed.

In the other animals with which we here occupy ourselves, the tibialis
anticus presents a complexity which would be incomprehensible unless
this muscle be first studied in the horse.

In this latter the tibialis anticus consists of two distinct portions,
placed one in front of the other: a fleshy portion, and a tendinous
portion running parallel to it.

The muscle is covered, except on its internal part and inferiorly, by a
muscle with which we will occupy ourselves later on--that is, the common
extensor of the toes.

The tendinous portion of the tibialis anticus (Fig. 83), especially
covered by the extensor of the toes, arises from the inferior extremity
of the femur, from the fossa situated between the trochlea and the
external condyle; thence it descends towards a groove which is hollowed
out on the external tuberosity of the tibia, and is directed towards the
tarsus, where it divides into two branches, which are inserted into the
cuboid bone and the superior extremity of the principal metatarsal.
These two parts form a ring through which the terminal tendon of the
fleshy portion of the same muscle passes.

This fleshy portion, situated behind the preceding, arises from the
superior extremity of the tibia, on the borders of the groove in which
the tendinous portion lies; thence it passes downwards for a short
distance on the inner side of the common extensor of the toes, which
covers it in the rest of its extent. It ends in a tendon which, after
passing through the tendinous ring above noticed, divides into two
branches. One of these branches is inserted into the anterior surface
of the superior extremity of the principal metatarsal, the other into
the second cuneiform bone.

[Illustration: FIG. 84.--MYOLOGY OF THE DOG: LEFT HIND-LIMB, EXTERNAL
ASPECT.

1, Biceps cruris and fascia lata, divided in order to expose the upper
part of the muscles of the leg; 2, inferior portion of the triceps
cruris; 3, patella; 4, semi-tendinosus; 5, inferior extremity of the
femur; 6, tibialis anticus (flexor of the metatarsus); 7, extensor
longus digitorum (anterior extensor of the phalanges); 8, tibia; 9,
peroneus longus; 10, peroneus brevis; 11, fifth metatarsal; 12,
fasciculus detached from the peroneus brevis and passing towards the
fifth toe; 13, external head of gastrocnemius; 14, tendo-Achillis; 15,
calcaneum; 16, flexor digitorum sublimis; 17, 17, tendon of the flexor
digitorum sublimis; 18, flexor longus pollicis (portion of the deep
flexor of the toes); 19, dorsal muscle of the foot (short extensor of
the toes).]

In the ox the same two portions of the tibialis anticus exist, but with
this capital difference--that the anterior portion is fleshy,
superficial, and blended for a great part of its length with the common
extensor of the toes.

The portion which corresponds to that which is fleshy in the horse
arises from the tibia; below, it ends on the inner surface of the
superior extremity of the metatarsus and the cuneiform bones. That which
represents the tendinous part, which is also fleshy, as we have just
pointed out, arises above with the common extensor of the toes, from the
femur, in the fossa situated between the trochlea and the external
condyle; whilst below, after having given passage to the tendon of the
preceding portion, as in the horse, it is inserted into the metatarsus
and the cuneiform bones.

In the pig, the tibialis anticus presents an arrangement nearly similar
to that which we have just described.

It seems to us of interest to add that it has been sought to ascertain
to what muscle of the human leg the tendinous part of the tibialis of
the horse corresponds--a part which has become fleshy in the pig and the
ox.

According to some authors, it represents the peroneus tertius; but that
muscle is situated on the outer side of the common extensor of the toes;
and here the portion with which it has been compared is placed on the
inside. It has also been likened to a portion of the common extensor of
the toes, but it does not pass to the latter. Lastly, it has been
considered as being the homologue of the proper extensor of the
great-toe; but why, then, in the ox, which has no great-toe, is it so
highly developed? Nevertheless, its position and its relations
sufficiently warrant this method of comprehending it. The tibialis
anticus is a flexor of the foot. It is also able, in animals in which
the tarsal articulations allow of the movement, to rotate the foot
inwards.

[Illustration: FIG. 85.--MYOLOGY OF THE OX: LEFT LEG, EXTERNAL ASPECT.

1, Gluteus maximus and biceps cruris; 2, semi-tendinosus; 3, patella; 4,
tibialis anticus (flexor of the metatarsus); 5, extensor longus
digitorum (anterior extensor of the phalanges); 6, fasciculus of the
extensor longus digitorum, which is considered as the representative of
the tendinous portion of the tibialis anticus in the horse; 7, peroneus
longus; 8, peroneus brevis (proper extensor of the external toe); 9,
external head of gastrocnemius; 10, soleus; 11, tendo-Achillis; 12,
calcaneum; 13, tendon of the extensor longus digitorum (superficial
flexor of the phalanges); 14, flexor longus pollicis and tibialis
posticus (deep flexor of the phalanges); 15, tendon of the superficial
flexor of the toes; 16, tendon of the deep flexor of the toes; 17,
suspensory ligament of the fetlock.]

With regard to the tendinous part, called by veterinarians the _cord of
the flexor of the metatarsus_, it serves, in the horse, to produce the
flexion of the metatarsus when the knee is already flexed; it thus acts
in a passive fashion, which is explained by its resistance and the
position which it occupies in relation to these two articulations.

=Extensor Proprius Pollicis.=--This muscle exists only in the dog and
the cat, and there in a rudimentary condition.

It is covered by the common extensor of the toes and the tibialis
anticus, and passes, accompanied by the tendon of this latter muscle, to
terminate on the second metatarsal, or the phalanx, which articulates
with it. When the first toe exists in the dog, it is inserted into this
by a very slender tendon.

=Extensor Longus Digitorum= (Fig. 83, 9; Fig. 84, 7; Fig. 85, 5, 6; Fig.
86, 4; Fig. 87, 12; Fig. 88, 7).--It is also called by veterinarians
_the anterior extensor of the phalanges_.

In the dog and the cat this muscle is to be seen in the space limited
behind by the peroneus longus and in front by the tibialis anticus.
Above it is covered by this latter. In the lower half of the leg, it is
also in relation, on the inner side, with the tibialis anticus; but
behind it is separated from the peroneus longus by the external surface
of the shaft and inferior extremity of the tibia. This arrangement,
besides, recalls that which is found in man, the peroneus longus of the
latter diverging in the same way, at this level, from the common
extensor, and leaving exposed the corresponding portion of the skeleton
of the leg.

This muscle, fusiform in shape, arises at its upper part from the
external surface of the inferior extremity of the femur, then its tendon
passes into a groove hollowed on the external tuberosity of the tibia.
The fleshy body which succeeds is directed towards the tarsus, but
before reaching it is replaced by a tendon. This tendon, at the level of
the metatarsal bones, divides into four slips, which pass towards the
toes, and are inserted into the second and third phalanges of the
latter.

In the horse it covers, to a great extent, the tibialis anticus, so that
it is the latter which forms the large fusiform prominence especially
noticeable in the middle region, to which the contour of the anterior
surface of the leg is due.

[Illustration: FIG. 86.--MYOLOGY OF THE HORSE: LEFT HIND-LIMB, EXTERNAL
ASPECT.

1, Semi-tendinosus; 2, biceps cruris; 3, patella; 4, extensor longus
digitorum (anterior extensor of the phalanges); 5, reinforcing band
arising from the ligament of the fetlock; 6, peroneus brevis (lateral
extensor of the phalanges); 7, external head of gastrocnemius; 8,
soleus; 9, tendo-Achillis; 10, calcaneum; 11, tendon of the superficial
flexor of the toes (superficial flexor of the phalanges); 12, flexor
longus pollicis and tibialis posticus (deep flexor of the phalanges);
13, 13, tendon of the superficial flexor of the phalanges; 14, 14,
tendon of the deep flexor of the phalanges; 15, suspensory ligament of
the fetlock; 16, principal metatarsal: 17, external rudimentary
metatarsal.]

It arises above from the inferior extremity of the femur, from the fossa
situated between the trochlea and the external condyle; therefore, it
has a common origin with the tendinous portion of the tibialis anticus,
or flexor of the metatarsus.

The tendon, which at the level of the inferior part of the leg succeeds
to the fleshy body, passes in front of the tarsus, the principal
metatarsal, and receives the tendon of the peroneus brevis which we will
describe later on. It then reaches the anterior surface of the fetlock.
There it presents an arrangement analogous to that which we have pointed
out in connection with the anterior extensor of the phalanges--a muscle
which, in the fore-limbs, corresponds to the common extensor of the
digits; that is to say, it is inserted, in form of an expansion, into
the pyramidal prominence of the third phalanx, after having formed
attachments to the first and second, and having received on each side a
strengthening band from the suspensory ligament of the fetlock.

In the ox the long extensor of the toes is united above, and for a great
part of its length, with the portion of the tibialis anticus, which
represents, albeit in the fleshy state, the tendinous cord of the latter
in the horse.

In common with this portion, it arises from the inferior extremity of
the femur. Thence it passes towards the tarsus and divides into two
fasciculi, internal and external, which are continued by tendons. These
pass towards the phalanges, and, in case of the common extensor of the
digits belonging to the fore-limbs, the internal is destined for the
internal toe, and the external is common to the two toes.

[Illustration: FIG. 87.--MYOLOGY OF THE DOG: LEFT HIND-LIMB, INTERNAL
ASPECT.

1, Semi-tendinosus; 2, semi-membranosus; 3, triceps cruris (vastus
internus); 4, sartorius (patellar); 5, sartorius (tibial); 6, patella;
7, first or middle adductor; 8, small and great adductor united; 9,
gracilis; 10, tibialis anticus (flexor of the metatarsus); 11, tibia;
12, tendon of extensor longus digitorum (anterior extensor of the
phalanges): 13, gastrocnemius, inner head; 14, tendo-Achillis; 15,
calcaneum; 16, popliteus; 17, superficial flexor of the toes; 18, flexor
longus pollicis (portion of the deep flexor of the toes); 19, flexor
longus digitorum (portion of the deep flexor of the toes); 20, tendon of
the tibialis posticus.]

[Illustration: FIG. 88.--MYOLOGY OF THE HORSE: LEFT HIND-LEG, INTERNAL
ASPECT.

1, Semi-tendinosus; 2, semi-membranosus; 3, triceps cruris (vastus
internus); 4, patella; 5, sartorius; 6, gracilis; 7, extensor longus
digitorum common extensor of the toes (anterior extensor of the
phalanges); 8, tendon of the preceding muscle; 9, reinforcing band given
off by the suspensory ligament of the fetlock; 10, tibialis anticus
(flexor of the metatarsus), its tendinous portion; 11, tibialis anticus
(flexor of the metatarsus), its fleshy portion; 12, cuneiform branch of
the tendon of this fleshy portion; 13, internal head of gastrocnemius;
14, popliteus; 15, tendon of the flexor brevis digitorum (superficial
flexor of the phalanges); 16, flexor longus pollicis and tibialis
posticus (deep flexor of the phalanges); 17, flexor longus digitorum
(oblique flexor of the phalanges); 18, 18, tendon of the superficial
flexor of the phalanges; 19, 19, tendon of the deep flexor of the
phalanges; 20, suspensory ligament of the fetlock; 21, principal
metatarsal; 22, internal rudimentary metatarsal.]

In the pig the general arrangement of the muscle is similar, but the
tendons end in a manner which is a little more complicated. Apart from
the fasciculi which correspond to the tendinous portion of the tibialis
anticus (fleshy here, as in the ox), the long extensor of the toes at
the level of the tarsus divides into three tendons: the internal goes to
the great internal toe; the middle bifurcates in the upper part of the
digital portion of the foot, and each of its branches goes towards one
of the great-toes; the external divides to pass towards each of the two
small toes, and towards the great ones; but this latter disposition is
not constant.

By its contraction the muscle which we have just studied extends the
phalanges and flexes the foot.

=Peroneus Tertius.=--This muscle is not found in domestic quadrupeds.

We should remember, nevertheless, that certain authors consider as
representing it the tendinous portion of the anterior tibial of the
horse, or the corresponding portion now fleshy, of the same muscle in
the pig and the ox. It is by reason of this fact that it is called the
third peroneal, notwithstanding that in the numerical order of the
peroneals it is rather the first.

But that which still further complicates this question of nomenclature
is that some authors give this name of third to a peroneal which, in the
carnivora, is situated more definitely in the group of external muscles
(see below, =Short Lateral Peroneal=).


Muscles of the External Region

In man, two muscles constitute this region; they are the peroneus longus
and peroneus brevis.

=Peroneus Longus= (Fig. 84, 9; Fig. 85, 7).--This muscle does not exist
in the domestic animals; only in the flesh-eaters, the pig and the ox
excepted.

It is in relation superiorly with the tibialis anticus, and inferiorly
with the common extensor of the toes; in the ox, it is in contact with
this latter muscle throughout its whole length.

The peroneus longus arises from the external tuberosity of the tibia;
towards the middle of the leg it is replaced by a tendon. This proceeds
towards the tarsus, but previously it passes between the tibia and
fibula. In the ox it is situated in front of the coronoid tarsal bone;
we recollect that this bone is regarded as representing the inferior
extremity of the fibula (see p. 97). Then it passes into a groove
belonging to the cuboid bone or to the cuboido-scaphoid bone in the ox,
traverses obliquely the posterior aspect of the tarsus, and is inserted
into the rudimentary bone which represents the first toe; or, if this
does not exist, into the innermost of the metatarsal bones.

This muscle is an extensor of the foot. It also rotates it outwards in
the animals in which the articulation permits this latter movement.

=Peroneus Brevis= (Fig. 83, 8; Fig. 83, 10; Fig. 84, 10; Fig. 86,
6).--In the dog and the cat, this muscle is covered in part by the
peroneus longus, and arises from the inferior half of the tibia and the
fibula; at the level of the tarsus it becomes tendinous, passes into a
groove hollowed out on the external surface of the inferior extremity of
the fibula, and terminates on the external aspect of the superior
extremity of the fifth metatarsal. A little before this insertion it
crosses the tendon of the long peroneal in passing to the outer side of
the latter.

To the short peroneal muscle is found annexed a very thin fasciculus
which lies upon it. This fasciculus arises from beneath the head of the
fibula, and is soon replaced by a thin tendon, which, accompanying that
of the short peroneal, proceeds towards the foot, after having traversed
the groove in the inferior extremity of the fibula; passes along by the
fifth metatarsal (Fig. 84, 12); blends at the level of the first phalanx
of the fifth toe with the corresponding tendon of the long extensor of
the toes, and partakes of the insertions of this tendon.

This fasciculus is designated by some authors under the name of the
peroneal of the fifth toe, or the proper extensor of the same toe. But
what makes still further complications is that other authors regard it
as an anterior, or third, peroneal. Now, these names are those which
other anatomists have applied to the fasciculus of the anterior tibial,
which, in the pig and the ox, is fused in part with the long extensor of
the toes. Hence there results a confusion which is truly regrettable.

In brief, we can, without inconvenience, consider it as a fasciculus of
the short peroneal muscle.

We sometimes find in man, but abnormally, an arrangement which partly
recalls that which we have just indicated. It consists in a duplication
of the tendon of the short peroneal, one of the branches of which goes
to the fifth metatarsal, and the other to the fifth toe; it is sometimes
a single fasciculus which goes to the phalanges of this latter. We have
met with examples of these anomalies.[31] In the pig, the short peroneal
is situated on the same plane as the long. It consists of two clearly
distinct fasciculi, which arise from the fibula. The tendon of the
anterior fasciculus proceeds to the great external toe--that is to say,
the fourth, of which it is the proper extensor. The posterior fasciculus
terminates on the small external toe, the fifth, of which it is in like
manner the extensor.

  [31] Édouard Cuyer, 'Anomalies, Osseous and Muscular' (_Bulletins de
       la Société d'Anthropologie_, Paris, 1891).

In the ox, the fleshy fibres of the short peroneal arise from a fibrous
band which replaces the fibula, and from the external tuberosity of the
tibia. Situated behind the long peroneal and on the same plane, it
terminates in a tendon which appears at the level of the inferior part
of the leg; it passes in front of the canon, and is inserted into the
external toe, of which it is the proper extensor.

In the horse, it is the sole representative of the peroneal muscles, and
veterinary anatomists have given it the name of _the lateral extensor of
the phalanges_.

Its fleshy body arises above from the external lateral ligament of the
knee-joint, and from the whole length of the fibula. In the middle third
of the leg it is narrowed; lower down it is replaced by a tendon. This
is lodged in a groove hollowed on the external surface of the inferior
extremity of the tibia; then after passing along the external surface of
the tarsus, it is directed forward, and proceeds to blend towards the
middle of the canon-bone with the tendon of the long extensor of the
toes, or anterior extensor of the phalanges, of which it shares the
insertions. It extends the phalanges into which it is inserted. It also
flexes the foot.


Muscles of the Posterior Region

It will not be unprofitable to recall to mind that, in man, the muscles
of this region are arranged in two layers: a superficial layer
consisting of the gastrocnemius and soleus, to which is added a muscle
of little importance, the plantaris, and a deep layer formed by four
muscles--the popliteus, flexor longus digitorum, tibialis posticus, and
flexor longus pollicis.

The gastrocnemius and soleus, independent in their upper portion, unite
below in a common tendon; they thus form also a triceps muscle, which we
designate under the name of the triceps of the leg, or triceps suralis,
because it forms the elevation of the calf of the leg (from _sura_,
calf).

=Gastrocnemius= (Fig. 83, 9, 11; Fig. 84, 13, 14; Fig. 86, 7, 9; Fig.
88, 13).--The external and internal heads of the gastrocnemius, distinct
from one another only in their upper portion, arise from the shaft of
the femur, above the condyles, on the borders of the popliteal surface,
to a relatively considerable extent in the great quadrupeds.

At this level they are situated in the popliteal region--that is to say,
in the space limited externally by the biceps, and internally by the
semi-tendinosus. But as they descend to a rather low level on the leg in
quadrupeds, and especially in carnivora, they do not, properly speaking,
determine a projection of the calf of the leg. However, they pass from
this region but to be soon continued by a tendon--the tendo-Achillis,
which is inserted into the calcaneum.

Now, the region of the tarsus is called by veterinarians _the ham_, the
posterior surface of which is angular, because of the oblique direction
of the leg with regard to the vertical direction of the metatarsus and
the presence of the calcaneum; the prominence which this surface
presents has received the name of _the point of the ham_, and the tendon
which ends there that of _the cord of the ham_.

But the tendo-Achillis does not alone form this cord. Indeed, as we will
soon see, the tendon of the superficial flexor of the toes takes part in
its formation.

We may add, with regard to the tendo-Achillis, that it is more clearly
perceived as an external feature, because the skin sinks in front of it,
as it does in man, over the lateral parts of the region which it
occupies.

The gastrocnemius, when it contracts, extends the foot on the leg.

It serves to maintain the tibio-tarsal angle in the standing position,
and during walking, to determine the steadying of the hind-limbs, which
then, after the fashion of a spring, project the body forward.

By an analogous movement they take part in the posterior projection of
the hind-limbs in the act of kicking; but they are not the only ones to
act in this case, the muscles of the buttock and thigh also being
brought into play.

=Soleus= (Fig. 83, 10; Fig. 86, 8).--This muscle, much less developed in
quadrupeds than in man, does not exist in the dog.

With regard to the soleus in the pig, Professor Lesbre says: 'Meckel
denied its existence; we, however, believe that it is united to the
external head of the gastrocnemius, its origin being transferred to the
femur.'[32]

  [32] F. X. Lesbre, 'Essai de Myologie comparée de l'homme et des
       mammifères domestiques en vue d'établir une nomenclature unique
       et rationelle,' Lyon, 1897, p. 169.

But in animals in which it exists, this muscle, of but little
importance, occupies the outer side of the leg. It arises above from the
external tuberosity of the tibia, and terminates below in a tendon which
is united with that of the gastrocnemius.

The soleus has the same action as these latter.

=Plantaris.=--In quadrupeds this muscle is blended with the superficial
flexor of the toes, which we will study afterwards.

=Popliteus= (Fig. 87, 16; Fig. 88, 14).--In man, this muscle, which
occupies the posterior surface of the tibia, above the oblique line, is
completely covered by the gastrocnemius.

In quadrupeds, where it is more voluminous, it projects internally
beyond the gastrocnemius, so that it is seen in the internal and
superior part of the region of the superficial layer of muscles,
immediately behind the internal surface of the tibia, which, as we know,
is subcutaneous.

The popliteus arises from the external surface of the external condyle
of the femur. Thence its fibres which diverge pass to be inserted into
the superior part of the posterior surface and of the internal border of
the tibia. It is in this latter region that it projects beyond the
gastrocnemius, but we may add that there it is more or less covered by
the semi-tendinosus.

It flexes the leg, and rotates it forwards.

=Superficial Flexor of the Toes= (Fig. 83, 13, 15; Fig. 84, 17; Fig. 86,
11, 13, 13; Fig. 87, 17; Fig. 88, 15, 18, 18).--In man, the homologue of
this muscle is found in the sole of the foot. It is called _the short
flexor of the toes_. It arises from the calcaneum, and passes to the
four outer toes. In quadrupeds, it rises as high as the back of the
knee, and is found blended with the plantaris.

Further designated by the name of _the superficial flexor of the
phalanges_, covered in part by the gastrocnemius, with which it is in
relation for a great part of the course which it traverses, this muscle
arises from the posterior surface of the femur, on the external branch
of the inferior bifurcation of the linea aspera. In the horse, this
origin takes place in a depression situated above the external condyle,
in the supracondyloid fossa. Then it accompanies the gastrocnemius, and
becomes tendinous where the tendo-Achillis commences. It then winds
round the latter in placing itself on its inner side, then on its
posterior surface, and reaches the calcaneum. It accordingly
contributes, as we have already pointed out, to form the cord of the
ham. After having become expanded, and having covered as with a sort of
fibrous cap the bone of the heel, it descends behind the metatarsus, and
presents there an arrangement analogous to that which we pointed out in
connection with the superficial flexor of the digits--that is, it
contributes to form the _tendon_. This prominence, in the form of a
cord, we see behind the canon-bone in solipeds and ruminants. It
finally terminates in the same way as the muscle with which we have
compared it (see p. 197).

In the horse, its fleshy body is but slightly developed, so that its
tendon alone is specially visible in the superficial muscular layer, but
in the dog and the cat it is large. Hence it results that its fleshy
body appears on each side of the inferior half of the gastrocnemius, and
produces an elevation which recalls that which the soleus produces on
each side of the same muscles in the human species.

The muscles which follow form, with the popliteus, which we have already
studied, the deep layer of the posterior region of the leg.

=Flexor Longus Digitorum= (Fig. 87, 19; Fig. 88, 17).--This muscle, in
man, is the only common flexor of the toes belonging to the muscles of
the leg.

In comparison with the preceding muscle, it is a deep flexor.
Veterinarians have given it the name of _the oblique flexor of the
phalanges_.

Visible on the internal aspect of the superficial layer of the muscles
of the leg, this muscle arises above from the posterior surface of the
external tuberosity of the tibia, becomes tendinous, passes towards the
metatarsus, and blends with the tendons of the posterior tibial and the
long proper flexor of the great-toe. In the dog and the cat it is
blended with this latter only.

=Tibialis Posticus= (Fig. 85, 14; Fig. 86, 12; Fig. 87, 20; Fig. 88,
16).--This muscle arises from the external tuberosity of the tibia, and
from the head of the fibula. Thence it passes to the tarsus, and
terminates in different fashion in carnivora and other quadrupeds.

In the dog and the cat, it is inserted into the ligamentous apparatus of
the tarsus, or into the base of the second metatarsal.

In the other quadrupeds with which we are here occupied it is blended
with the long proper flexor of the great-toe.

It is accordingly in the carnivora that the mode of termination of the
tibialis posticus most nearly resembles that of this same muscle in the
human species. From this independence there results a special action.

It is an adductor and internal rotator of the foot.

=Flexor Longus Pollicis= (Fig. 84, 18; Fig. 85, 14; Fig. 86, 12; Fig.
87, 18; Fig. 88, 16).--This muscle, as that in man, is the most external
of the deep layer of the leg. It is on the external aspect of the latter
we perceive it, between the peroneals and the gastrocnemius or
tendo-Achillis.

It arises from the fibula and tibia, and is thence directed towards the
tarsus. It unites with the long common flexor of the toes to form with
it _the deep flexor of the phalanges_, of which it is the principal
fasciculus. We may add that in the dog and the cat the posterior tibial
remains independent of this latter, but that in the pig, ox, and horse
the posterior tibial is united to the preceding to form with them the
deep flexor muscle.

Thus constituted, the deep flexor goes towards the phalanges, where it
terminates as the deep flexor of the digits of the fore-limbs (see p.
197). In animals possessed of a canon it contributes to form the
_tendon_ (Fig. 85, 16; Fig. 86, 14, 14; Fig. 88, 19, 19).


Muscles of the Foot

We must remember that on the dorsal surface of the foot in man we find
but a single muscle--the dorsalis pedis. The remaining subcutaneous
structures of this region consist of the tendons of the anterior muscles
of the leg which occupy this dorsal aspect.

=Dorsalis Pedis= (Fig. 84, 19).--Also called the extensor brevis
digitorum, the dorsalis pedis muscle is found in all domestic
quadrupeds; but its development is so much the less as the number of
digits is more reduced.

In the dog and the cat it arises from the calcaneum, and is inserted
into the three internal toes (the first toe excepted) by uniting with
the corresponding tendons of the common extensor.

In the pig its disposition is analogous.

As for the dorsalis pedis of the ox and the horse, it is extremely
rudimentary, and occupies the superior part of the canon. It is a small,
fleshy body, situated on the anterior surface of the metatarsus, which
arises from the calcaneum, whence it passes to unite at its inferior
extremity with the tendon of the extensor of the phalanges.

As regards the muscles of the sole of the foot, we think it unnecessary
to occupy ourselves at any length with them because of their slight
importance with regard to external form.

We will only recall that in the median portion of this plantar surface
we find in man the short flexor of the toes, which in quadrupeds arises
higher up, from the posterior surface of the femur; that it belongs to
the muscles of the leg; and that it forms the superficial flexor of the
toes, which we have already studied.

We may further add that the suspensory ligament of the fetlock in
ruminants and solipeds represents, as in the fore-limbs, the
interosseous muscles.


MUSCLES OF THE HEAD

We will divide these muscles into two categories: masticatory and
cutaneous.


Masticatory Muscles

The muscles of this group which specially interest us are the masseter
and the temporal. As regards the pterygoids, since they are situated
within the borders of the inferior maxillary bone, and consequently do
not reach the surface, we shall not require to occupy ourselves with
them here.

=Masseter= (Fig. 89, 2; Fig. 90, 1; Figs. 91, 92).--For those who have
studied the masseter of man, it is not difficult to recognise that of
quadrupeds. Nevertheless, the particular aspect which it presents in
different species gives to its study a certain interest.

Arising from the zygomatic arch, and passing downwards and backwards, it
is inserted into the external surface of the ramus of the mandible and
into its angle.

Its posterior border is in relation with the parotid gland (Fig. 90, 14;
Figs. 91, 92), this gland being situated between the corresponding
border of the lower jaw bone and the transverse process of the atlas.
Such are the general characters; the following are the particular ones:

In the carnivora it is thick and convex. In the horse it is flat, but
more expanded; it forms the _flat of the cheek_. In the ox it is flat,
as in the latter; but, while being less thick, it is more prolonged in
the vertical direction.

The form of the osseous parts which give it origin is, besides, in
relation with these differences, and explains the peculiar characters
which the masseter presents.

[Illustration: FIG. 89.--MYOLOGY OF THE DOG: MASTICATORY MUSCLES (A
DEEPER DISSECTION THAN THAT SHOWN IN FIG. 90).

1, Zygomatic arch; 2, masseter; 3, temporal exposed by the suppression
of the auricular and occipital muscles and the pinna of the ear; 4,
auditory canal; 5, inferior maxillary bone; 6, digastric.]

Indeed, in the dog and the cat the zygomatic arch, strongly convex,
springs up in a marked manner from the plane of the lateral aspects of
the skull.

In the horse the same arch, less prominent externally, is prolonged by a
rectilinear crest on the superior maxillary bone, where it is continued
in forming the zygomatic or maxillary spine.

In the ox the same crest ascends a good way towards the inferior margin
of the orbit in a curved direction with the concavity inferior, to
redescend afterwards on the external surface of the superior maxilla.

The masseter is an elevator of the lower jaw. It acts, above all, as in
the human species, in the process of mastication.

=Temporal Muscle= (Fig. 89, 3).--The development of the temporal is in
proportion to the energy of the movements of elevation which the lower
jaw has to execute.

It arises from the temporal fossa, and is inserted into the coronoid
process of the inferior maxilla.

Its development, enormous in the carnivora, is such that the muscle
projects beyond its fossa. It is less voluminous in the horse, and still
less so in the ox. In the latter, indeed, the temporal fossa, although
deep, is of small extent (see Fig. 62, p. 119); the frontal bone being
large, it is found to be thrown back on the lateral walls of the
cranium, below the osseous processes which support the horns and
overhang the fossa in question, as well as the muscle which it contains.

It is covered by the auricular muscles, and by the base of the pinna of
the ear.

Like the masseter, the temporal is an elevator of the lower jaw.


Cutaneous Muscles of the Head

=Occipito-Frontalis.=--The epicranial aponeurosis is extremely thin. In
the dog the occipital muscle occupies the superior part of the head; it
overlies the temporal muscle.

With regard to the frontal muscle, which is of great extent in the ox
(Fig. 91, F), it is represented in the horse and the carnivora by a
small fleshy fasciculus only, the _fronto-palpebral muscle_, similar to
the superciliary muscle. This, occupying the superior and internal part
of the border of the orbit, ends by blending its fibres with those of
the orbicular muscle of the eyelids at the region of the eyebrow.

=Orbicularis Palpebrarum= (Fig. 90, 2; Figs. 91, 92).--This annular
muscle surrounds the palpebral orifice, and takes its origin on the
internal part of the orbital region. In the horse it arises, by a small
tendon, from a tubercle which occupies the external surface of the os
unguis, or lachrymal bone.

This muscle determines the narrowing and closure of the palpebral
orifice.

=Pyramidalis Nasi.=--The pyramidal muscle is not found in the domestic
animals. It appears to be blended with the internal elevator of the
upper lip and wing of the nose; this is easy of comprehension if we bear
in mind the relative position of these two muscles in the human species.

[Illustration: FIG. 90.--MYOLOGY OF THE DOG: MUSCLES OF THE HEAD.

1, Masseter; 2, orbicularis palpebrarum; 3, zygomaticus major; 4,
lachrymal (this muscle is sometimes described under the name of the
small zygomatic); 5, levator labii superioris proprius; 6, levator
labii superioris alæque nasi; 7, caninus; 9, buccinator; 11,
zygomatico-auricularis; 12, external temporo-auricularis; 14, parotid
gland; 15, parotido-auricularis; 16, inferior maxillary bone; 17,
digastric.]

=Corrugator Supercilii.=--This muscle is represented by the
fronto-palpebral muscle noticed above, which is by some regarded as a
vestige of the frontal.

=Zygomaticus Major= (Fig. 90, 3; Figs. 91, 92).--This is the
_zygomatic-labial_ of veterinarians. This muscle is of an elongated
form, and has a ribbon-like aspect.

In the dog and the cat it arises from the base of the pinna of
the ear, from the portion of this base which bears the name of
scutiform cartilage. (With regard to this cartilage, see p. 242,
=Zygomatico-auricularis=.) From this it is directed downwards and
forwards, to terminate, after having crossed the masseter, on the deep
surface of the skin of the corresponding labial commissure.

This mode of termination is the same in the ox and the horse; but where
the muscle differs is at the level of its upper extremity. There it
ascends less than in the carnivora. In the ox it arises from the
zygomatic arch in the neighbourhood of the temporo-maxillary
articulation; in the pig and the horse its origin is still lower, on the
surface of the masseter, close to the maxillary spine.

When it contracts, it draws upwards the labial commissure.

Now, in man, we remember, it is the great zygomatic that, by an action
of the same kind, determines the essential characters of the expression
of laughing.

There is, accordingly, a connection to be established between those
displacements which are similar and the analogy of facial expression
which necessarily results from them.[33]

  [33] Édouard Cuyer, 'The Mimic,' Paris, 1802.

=Zygomaticus Minor= (Fig. 90, 4; Figs. 91, 92).--The existence of this
muscle has not been clearly demonstrated. Nevertheless, Straus-Durckheim
noted its presence in the horse, and described it as 'a muscle arising
by two heads, of which one, the superior, arises from the malar bone
below the orbit, and passes downwards and forwards over the
fibro-adipose layer which supports the moustache. The second, the
inferior, arises from the alveolar border in front of the second molar
tooth, and passes forward to be inserted into the same fibro-adipose
layer.'[34]

  [34] H. Straus-Durckheim, 'Anatomie descriptive et comparative du
       chat,' Paris, 1845, t. ii., p. 210.

In connection with other quadrupeds, it is described by certain authors
as a very thin muscle, arising below the cavity of the orbit, where it
is blended with the fibres of the internal elevator of the upper lip and
the ala of the nose; thence it proceeds to terminate below by uniting
with the subcutaneous muscle. But this muscle is regarded by other
authors as the lachrymal muscle, which does not exist in this state in
man, but of which the development is particularly remarkable, as to
extent, in the ox, in which it descends as far as the buccinator.

According to other authors, some of the fibres of this muscle constitute
the small zygomatic.

[Illustration: FIG. 91.--MYOLOGY OF THE OX: MUSCLES OF THE HEAD.

1, Masseter; 2, orbicularis palpebrarum; F, frontalis; 3, zygomaticus
major; 4, lachrymal (this muscle is sometimes described under the
name of small zygomatic); 5, levator labii superioris proprius; 6,
levator labii superioris alæque nasi; 7, levator anguli oris or
caninus; 8, orbicularis oris; 9, buccinator; 10, maxillo-labial; 11,
zygomatico-auricularis; 12, external temporo-auricularis; 14, parotid
gland; 15, parotido-auricularis; 16, inferior maxillary bone.]

=Levator Labii Superioris Proprius= (Fig. 90, 5; Figs. 91, 92).--Also
named by veterinarians the _supramaxillo-labial_, or again, the _proper
elevator of the upper lip_, this muscle arises from the external surface
of the superior maxillary bone, passes under the superficial elevator,
which we shall study in the succeeding paragraph, and goes to be
inserted into the thickness of the lip, to which its name indicates that
it belongs.

The peculiarities of this muscle in different animals are the following:

In the dog and the cat it arises behind the infra-orbital foramen.

In the pig it arises from a depression below the orbital cavity, and its
fleshy body is terminated in front by a strong tendon in the upper part
of the snout, in which it divides into fasciculi.

In the ox it arises from the maxillary spine.

In the horse it arises below the orbital cavity; then, after having
crossed the superficial elevator, it ends in a tendinous expansion,
situated in the median line between the nasal fossæ. This expansion
divides into fasciculi, which end in the thickness of the upper lip.

By the contraction of this muscle, the lip is raised, on one side only,
if a single muscle contracts, or in its whole extent, if the two muscles
act simultaneously.

=Internal Elevator (or Superficial) of the Upper Lip and the Wing of the
Nose= (_levator labii superioris alæque nasi_) (Fig. 90, 6; Figs. 91,
92).--This is the muscle veterinarians designate _the supranaso-labial_.

Arising from the frontal and nasal bones, it thence passes towards the
upper lip, where it is inserted as well as into the wing of the nose.

In the ox it is united above with the frontal muscle, and below is
divided into two fasciculi, between which pass the elevator described
above and the canine muscle.

In the horse it is also divided into two fasciculi; but the arrangement
is the opposite as regards, their relations with neighbouring muscles,
in this animal and in the preceding.

In the ox the external fasciculus is covered by the external elevator
and the canine, which pass under the internal fasciculus; in the horse
the deep elevator passes under the two fasciculi, and the canine passes
under the external bundle, and afterwards covers the internal.

In the pig, the internal elevator is wanting.

As its name indicates, it raises the upper lip and the wing of the
nose.

=Transversus Nasi.=--In the horse this muscle, which is very thin, is
situated on the dorsum of the nose, and proceeds to be inserted into the
cartilaginous skeleton of the nostrils. In the pig, it occupies an
analogous situation. It does not exist in the ox or in carnivora. The
transversus nasi is a dilator of the nostrils.

[Illustration: FIG. 92.--MYOLOGY OF THE HORSE: MUSCLES OF THE HEAD.

1, Masseter; 2, orbicularis palpebrarum; 3, zygomaticus major; 4,
lachrymal (this muscle is sometimes described under the name of the
small zygomatic); 5, external elevator (or deep) of the upper lip and
ala of the nose; 6, internal elevator (or superficial) of the upper lip
and of the ala of the nose; 7, levator anguli oris or caninus; 8,
orbicularis oris; 9, buccinator; 10, maxillo-labialis; 11,
zygomatico-auricularis; 12, temporo-auricularis externus; 13,
cervico-auricularis; 14, parotid gland; 15, parotido-auricularis; 16,
inferior maxillary bone.]

=Caninus= (Fig. 90; Figs. 7, 91, 92).--This is the muscle called by
veterinarians _the great supramaxillo-nasal_.

In the dog and the cat it is situated below the inferior border of the
external elevator of the upper lip, of which it follows the direction.
It arises, as does this latter, from the external surface of the
maxilla, and goes also to terminate in the upper lip by blending with
the internal elevator of this lip and of the alæ of the nose. It raises
the upper lip.

In the ox, it arises from the maxillary spine, and then divides into
three parts; the superior passes under the internal portion of the
internal elevator of the upper lip and the alæ of the nose, and goes
into the nostril; whilst the two others, situated lower down, terminate
in the upper lip.

In the pig, it is formed of two superimposed fasciculi, which arise from
the spine of the maxilla and the impressions in front of it. These two
fasciculi terminate in the snout, which they move laterally.

In the horse, it is situated at a certain distance from the external
elevator; in the preceding animals it is in contact with the latter.
Arising behind from the external surface of the maxilla, in front of the
maxillary spine, it is directed towards the anterior part of the face,
passes under the external portion of the internal elevator (it is the
opposite of this in the ox), and proceeds, on expanding, to terminate in
the skin of the nostril. By its contraction it dilates the latter.

=Orbicularis Oris= (Fig. 91, 8; Fig. 92).--This muscle, very fleshy in
the solipeds and the ruminants, is arranged as a ring round the buccal
orifice, in the thickness of the lips, where it is blended with the
other muscles of this region.

Having for its function the narrowing of the orifice it surrounds, it
acts during suction and in the prehension of food.

=Triangularis Oris.=--This muscle does not exist in domestic quadrupeds.

=Quadratus Menti.=--In the pig and the carnivora, it arises from the
anterior part of the body of the inferior maxillary bone, and passes at
the other end to terminate in the corresponding portion of the lower
lip, which it depresses by its contraction.

In the ox and the horse this muscle does not exist; it is replaced for
the depression of the lower lip, which it affects in other animals, by
supplemental fibres of the buccinator.

=The Prominence of the Chin.=--Below the lower lip in the horse is
situated the so-called _prominence of the chin_, limited posteriorly by
the _beard_, a depressed region which gives point to the curb of the
bridle.

The prominence, which also exists in the ox, is a fibro-muscular pad
which blends with the orbicular muscle of the lips, and receives on its
superior aspect the insertion of the two muscles (_levator menti_) by
which it is suspended. These arise, above, on each side of the symphysis
of the inferior maxillary bone. They raise the lower lip with force, and
they are the agents which, as we can sometimes observe in the horse,
make it click against the upper lip, suddenly projecting it upwards.
This action sometimes becomes a habit, and its continuance constitutes a
vice.

A corresponding structure is found in the pig and in the carnivora, but
in them it does not produce an external prominence such as we have
described.

=Buccinator= (Fig. 90, 9; Figs. 91, 92).--Further designated by the name
of _alveolo-labial_, this muscle is situated on the lateral portions of
the face, in the thickness of the cheeks. It consists of two layers, one
superficial and the other deep.

The deep portion arises from the portion of the alveolar border of the
superior maxillary bone which corresponds to the molar teeth, and from
the anterior border of the ramus of the mandible. Thence it is directed
forwards, passes under the superficial layer, and blends with the fibres
of the orbicular muscle of the lips. To this part of the buccinator some
authors give the name of molar muscle.

The superficial portion is formed by fibres which pass from the alveolar
border of the superior maxillary bone to the corresponding border of the
opposite bone. It is very highly developed in the herbivora.

This muscle acts especially during mastication; it serves to press back
again under the molar teeth the portions of food which fall outside the
dental arch.

In the pig, the ox, and the horse, a muscle which is considered as
supplemental to the buccinator is placed along the inferior border of
the latter.

This muscle, which we describe separately under the names of
_maxillo-labialis_ (Fig. 91, 10; Fig. 92) and _depressor of the lower
lip_, is clearly distinct from the buccinator, especially in the horse.
It arises, behind, with the deep layer of the muscle to which it is
annexed, from the anterior border of the ramus of the lower jaw; in
front it terminates in the thickness of the lower lip.

In the ox, it is more intimately united with the buccinator.

It depresses the lip to which it is attached, and displaces it laterally
when it acts on one side only.

In the human species, the pinna of the ear being generally immobile, the
muscles which belong to it are, very naturally, considerably atrophied.
Accordingly, the auricular muscles, anterior, superior, and posterior,
are reduced to pale and thin fleshy lamellæ, whose action is revealed in
certain individuals, only in a way which may be said to be abnormal.

It is not the same in quadrupeds. The pinna of the ear is extremely
mobile, and its displacements have a real value from the point of view
of physiognomical expression. It is therefore necessary to review the
muscles which move this pinna without giving them, at the same time,
more importance than they merit, since in themselves they do not
determine the formation of surface reliefs, which are sufficiently
apparent.

Notwithstanding that for certain of these muscles it is possible to
trace their analogy with those of the auricular region of man, it is
very difficult, because of their complexity, to trace this analogy for
all. This is why we shall not be able here, as we have done for the
other muscles of the subcutaneous layer, to give at the head of each
paragraph the name of a human muscle, and then to group in the same
paragraph the muscles which correspond to it in different quadrupeds.
Therefore the nomenclature and the divisions adopted for these latter
must serve us as a base or starting-point.

Because the pinna of the horse's ear is so very mobile, we will first
begin with a study of its auricular muscles.

=Zygomatico-auricularis= (Fig. 92, 11).--This muscle, which is formed of
two small bands of fleshy fibres, arises from the zygomatic arch in
blending with the orbicular muscle of the eyelids; thence it is
directed towards the base of the pinna of the ear, and is inserted into
this base, and also into the cartilaginous plate situated in front of
and internal to this, and resting on the surface of the temporal muscle;
this is the scutiform cartilage.

The zygomatico-auricularis, which we look on as the homologue of the
anterior auricular of man, draws the pinna of the ear forwards.

=Temporo-auricularis Externus= (Fig. 92, 12).--This, which is thin and
very broad, covers the temporal muscle.

It arises from the whole extent of the parietal crest, blending in this
plane, in its posterior half, with the muscle of the opposite side.
Thence it is directed outwards towards the pinna of the ear, and is
inserted into the internal border of the scutiform cartilage and on the
inner side of the concha--that is to say, of the conchinian
cartilage--which forms the principal part of the pinna. We are
supposing, in the description of the muscles which move it, that this
pinna has its opening directed outwards.

The external temporo-auricular, which recalls, from its situation, the
superior auricular of man, is an adductor of the ear; besides, it causes
it to describe a movement of rotation from without inwards, so as to
direct its opening forwards.

=Scuto-auricularis Externus.=--This muscle may be considered as
supplementary to the external temporo-auricular; the concha fasciculus
of this latter partly covers it.

Extending from the scutiform cartilage to the inner side of the concha,
it contributes to the movement of rotation by which the opening of the
pinna of the ear is directed forwards.

=Cervico-auricular Muscles= (Fig. 92, 13).--These muscles, three in
number, are situated behind the pinna of the ear; they are called, from
their mode of superposition, the superficial, middle, and deep.

These arise, all three, from the superior cervical ligament, and pass
from there towards the cartilage of the concha. They recall, as regards
situation, the posterior auricular muscle of man.

=Superficial Cervico-auricular= (_Cervico-auricularis
superioris_).--This muscle, inserted into the posterior surface of the
concha, draws this cartilage backwards and downwards.

=Middle Cervico-auricular= (_Cervico-auricularis medius_).--Situated
between the two other muscles of the same group, it proceeds, after
having covered the superior extremity of the parotid gland, to be
inserted into the external part of the base of the concha. It determines
the rotation of this concha in such a way as to direct the opening of
the ear backwards.

=Deep Cervico-auricular= (_Cervico-auricularis inferioris_).--Covered by
the preceding muscle and the superior portion of the parotid, it is
inserted into the base of the pinna of the ear, and has the same action
as the middle cervico-auricular.

=Parotido-auricularis= (Fig. 92, 15).--This is a long and thin fleshy
band which arises from the external surface of the parotid gland, and
tapering as it passes upwards towards the pinna of the ear, is inserted
into the external surface of the base of the concha, below the inferior
part of the angle of reunion of the two borders which limit its opening.

It inclines the pinna outwards; it is, accordingly, an abductor of the
pinna.

=Temporo-auricularis Internus.=--This muscle is covered by the external
temporo-auricular and the superior cervico-auricular. It arises from the
parietal crest, and is inserted into the internal surface of the concha.
It is an adductor of the pinna of the ear.

There are, finally, an internal scuto-auricular muscle and a
tympano-auricular; but they do not present any interest for us; we can
simply confine ourselves to making mention of them.

In the ox, because of the situation of the temporal fossa and the fact
that the external temporo-auricular muscle is applied, as in the horse,
over the muscle which this fossa contains, this temporo-auricular muscle
does not reach the middle line (Fig. 91, 12).

But in the cat and the dog this muscle covers all the upper part of the
head (Fig. 90, 12). It is divided into two parts: the interscutellar and
the fronto-scutellar.

The interscutellar is a single muscle, thin and broad, covering the
temporal muscle and a portion of the occipital, extending from the
scutiform cartilage of the pinna of one side to the same cartilage of
the pinna belonging to the side opposite. It approximates the two pinnæ
to one another by bringing them each into the position of adduction.

The fronto-scutellar arises from the orbital process of the frontal
bone, and from the orbital ligament, which at this level completes the
interrupted osseous boundary of the orbital cavity. Thence it is
directed, widening as it proceeds, towards the scutiform cartilage, and
is there inserted by blending with the corresponding part of the great
zygomatic. Its action is analogous to that of the preceding muscle; but,
further, it directs the opening of the pinna forwards.

These are the muscles which act, for example, when the dog, having his
attention strongly attracted by any cause, pricks up his ears and turns
the openings forward, in order the better to understand every sound
which proceeds, or may possibly proceed, from that which he observes.
From this, which may be extremely well seen in some individuals, results
the appearance of vertical wrinkles of the skin in the interval between
the pinnæ of the ears, these being caused by the folding of the
integument, whilst the pinnæ approach one another. These movements, with
which are associated fixation of look and a widening of the palpebral
fissure, produce a peculiarly expressive look; this is why they merit
our attention.

=Zygomatico-auricularis= (Fig. 90, 11).--Arises from the internal
surface of the great zygomatic, passes towards the pinna of the ear, and
goes to be inserted into the external part of the base of the pinna,
below its opening, to a prominence which corresponds to the antitragus
of the human ear. It is to this antitragus, but proceeding from another
direction, that the parotido-auricular muscle is inserted (Fig. 90, 15).

With regard to the cervico-auriculars, they are all three present. The
superior, or superficial, situated behind the interscutellar portion of
the external temporo-auricular, has its origin on the median line of the
neck; thence it passes towards the pinna of the ear, blending its fibres
with those of the interscutellar muscle, and is inserted into the
scutiform cartilage and the internal surface of the pinna.

Such are the principal muscles of the ear in the carnivora; it would
seem to us superfluous to dwell on the others of this region, so that we
will here conclude the study of the muscles in general, and that of the
myology of the head in particular.




CHAPTER III

EPIDERMIC PRODUCTS OF THE TERMINAL EXTREMITIES OF THE FORE AND HIND
LIMBS


We will first recall to mind that among the quadrupeds some are found of
which the fingers and toes have their third phalanges terminated by
claws--these are the unguiculates; and that in others the terminal
extremity of each limb is completely encased in a horny envelope, the
hoof--these are the ungulates.

In the first group, the claws remind us to a certain extent of the
arrangement of the nails in man; the inferior aspect of the paws is
covered by an epidermic layer, thick and protective, which may be
likened to the skin, correspondingly thick, which covers in the greater
part of its extent the plantar surface of the foot in the human species.

In the second group, the surface by which the third phalanx rests on the
ground is correspondingly protected, but this time by a layer of horn
which belongs to the hoof.

After the preceding remarks, our study will be found to fall into a
natural division, and it is in the order which we have just followed for
the purpose of indicating its existence that we now proceed to study the
nature and form of the different elements which complete or protect the
digital extremities of the thoracic and abdominal limbs.

=Claws.=--These horny coverings of the third phalanges, which we have to
consider only in the dog and cat, may be compared with the nails of man,
with which, however, they present, as is well understood, characteristic
differences.

The claws are compressed laterally, curved on themselves, and are
terminated in front by a sharp point in the felide, but more blunted in
the dog. Their superior border is convex and thick. We may say,
therefore, that a claw is a sort of hollow tube, in the form of a cone
flattened in the transverse direction, in which the third phalanx is
set, and which is itself set in a groove formed by a kind of osseous
hood which occupies the base of this third phalanx (see Fig. 37, p. 57).

This definition is exact, as regards the general appearance; but, when
more closely scrutinized, it is not sufficient. The tube in question is
not formed of a single piece; each of the claws is formed by a lamina
laterally folded, but of which the borders are not exactly joined
together inferiorly; they leave between them a small interval, and this
is filled by a layer of more friable horny substance, to which has been
given the name of plantar nail. This arrangement, which is clearly
defined in the dog (Fig. 93), is comparable to that which we shall
afterwards meet with in connection with the sole of the hoof of the
horse (see Fig. 100, p. 257). In the dog and the cat, the weight of the
limb resting on the inferior surface of the phalanges, it was necessary
that the region of the plantar surface of the foot corresponding to
these latter should be protected; this is the function of certain
fibro-adipose pads, which are situated there, and which are designated
by the name of _plantar tubercles_.

=Plantar Tubercles= (Fig. 94).--These tubercles, or dermic cushions, are
divided, in each paw, into _tubercles of the digits_ (or of the toes), a
_plantar tubercle_, and, on the fore-limbs, a _tubercle of the carpus_.

The tubercles of the fingers (or of the toes) are of the same number as
the latter. That which belongs to the thumb is but little developed, but
the others are more so. They are in relation with the plantar surfaces
of the second and third phalanges, so that when the paw is in contact
with the ground the articulation which, in each of the fingers or toes,
joins these phalanges, rests on the corresponding pad.

The plantar tubercle is larger than the preceding. It is of a more or
less rounded form; sometimes it is triangular, and then comparable in
outline to the ace of hearts, the point of which is, in this case,
turned towards the claws; its margin being sometimes strongly indented,
it may also have a trilobate form. It is on it that rest the
metacarpo-phalangeal or metatarso-phalangeal articulations, according to
the limb studied. The tubercle of the carpus, situated at the level of
the posterior surface of this latter, is less important than the
preceding, the region which it occupies not reaching the ground during
walking. But it is not to be neglected from the point of view of
external form, because of the prominence which it produces.

[Illustration: FIG. 93.--CLAW OF THE DOG: INFERIOR SURFACE.

1, Horny lamina of the claw; 2, plantar nail; 3, tubercle of the
corresponding digit.]

[Illustration: FIG. 94.--LEFT HAND OF THE DOG: INFERIOR SURFACE, PLANTAR
TUBERCLES.

1, 1, 1, 1, 1, Tubercles of the fingers; 2, plantar tubercle; 3,
tubercle of the carpus.]

In the ungulates the terminal extremity of the limb is, as we have above
pointed out, enclosed in a horny envelope which is no other than the
hoof.

We will first study the hoof of the horse--a hoof which is single for
each of the limbs, inasmuch as in this animal each of these has but a
single digit.

=Hoofs of the Solipeds.=--We will first study the hoof as regarded in a
general way--that is, without taking into account the limb to which it
belongs. We will afterwards point out the differences presented when the
hoofs of the fore and hind limbs are compared.

In connection with the external forms of the horse, the study which we
are now commencing is of great importance. But, before entering upon it,
it appears to us necessary to rapidly examine what the hoof contains
(Fig. 95).

[Illustration: FIG. 95.--VERTICAL ANTERO-POSTERIOR SECTION OF THE FOOT
OF A HORSE.

1, Third phalanx; 2, fibro-cartilage; 3, podophyllous tissue; 4,
inferior part of the wall; 5, section of the wall of the hoof; 6,
cutigerous cavity; 7, tendon of the anterior extensor of the phalanges;
8, reinforcing band coming from the suspensory ligament of the fetlock;
9, tendon of the superficial flexor of the phalanges; 10, tendon of the
deep flexor of the phalanges.]

In the interior of this horny box we find the third phalanx, a small
sesamoid bone placed opposite to the posterior border of the latter, a
portion of the inferior extremity of the second phalanx, and the
tendons, which terminate at this region.

To the third phalanx are added two fibro-cartilaginous plates, flattened
laterally, which prolong backwards the bone to which they are annexed.
The inferior border of each of these fibro-cartilages is fixed by its
anterior part to two osseous prominences situated at each of the angles
which terminate the small phalanx behind; these prominences are: _the
basilar process_ and _the retrorsal process_ (Fig. 96); by its posterior
part, this border is continuous with a structure known as _the plantar
cushion_ (see further on).

The posterior border is directed obliquely upwards and forwards. The
superior border, which is convex or rectilinear, is thin, and is
separated from the posterior border by an obtuse angle. Finally, the
anterior border, which is directed obliquely downwards and backwards, is
united to the ligamentous apparatus, which keeps the second and third
phalanges in contact.

These fibro-cartilages, at their upper extremities, project beyond the
hoof, and therefore assist in the formation of the lateral regions of
the foot,[35] at the part which is called the _crown_. They project less
above the hoof in the posterior limbs.

  [35] Here, for the first time, apropos of the hoof, we use the word
       'foot.' As in osteology and in myology we have, for the sake of
       clearness of comparison, designated under this name the region
       limited above by the tarsus, it is necessary to point out here
       that we employ the same word for a more restricted region. This
       we did in conformity with the usage of veterinarians, who so
       designate the region of the hoof. It is necessary to explain this
       double employment of the word, and, further, to show the
       particular meaning ascribed to it.

[Illustration: FIG. 96.--THIRD PHALANX OF THE HORSE: LEFT ANTERIOR LIMB,
EXTERNAL SURFACE.

1, Pyramidal eminence; 2, surface, for articulation with the inferior
extremity of the second phalanx; 3, basilar process; 4, retrorsal
process.]

The posterior and inferior borders of these cartilages meet at an acute
angle. The angle so formed, or cartilaginous bulb, constitutes the base
of the region, which is commonly called the _heel_--a part of the foot
which, as its name implies, is situated posteriorly, but which we must
not confound, as we might be led to do, with the region occupied by the
calcaneum. We know from our previous studies of comparative osteology
that this latter is situated much higher up.

The _plantar cushion_ is a sort of fibrous wedge which occupies the
interval bounded by the fibro-cartilaginous plates which we have just
been studying. Its inferior surface, the form of which we shall find to
be reproduced by a portion of the corresponding surface of the hoof, is
prolonged anteriorly into a point, while behind it is divided into two
branches, which, diverging from one another, join the posterior angles
of the fibro-cartilages. These two branches are separated by a median
excavation.

The different constituent elements which we have just been discussing
give elasticity to the foot.

To finish the examination of the parts contained in the hoof, we will
add that among them is also found what is called the fleshy _envelope_,
or _flesh_ of the foot.

We divide the latter into three regions: the podophyllous tissue,
striated or laminated flesh which is spread out over the anterior
surface of the third phalanx; the pad, or the hardened skin which
corresponds to the upper border of the hoof, and forms a prominence
above the podophyllous tissue; and the villous flesh, or velvety tissue
which covers the plantar surface of the third phalanx and the plantar
cushion. These three tissues form as a whole the keratogenic
membrane--that is to say, that which produces horny tissue, and
consequently regenerates the hoof.

It is this latter that we now proceed to study.

When we examine its anterior surface or the opposite one, the hoof of
the horse has the shape of a truncated cone with the base below and the
summit cut off obliquely downwards and backwards (Fig. 97).

Viewed on one of its lateral aspects, it may be compared to a truncated
cylinder placed on the surface of the section (Fig. 98). We particularly
call attention to this latter comparison, for it singularly aids us in
making a representation of the foot of the horse when viewed laterally.

Notwithstanding that the hoof forms apparently a homogeneous whole, it
consists of three parts, which may be separated from one another by
maceration. The indication of such disunion, artificially produced, may
seem useless. It is not so, however, for this division of the hoof will
permit us to carry out the study of the latter in a clearer, and
consequently a more satisfactory, way. The three parts in question are
the _wall_, or _crust_, the _sole_, and the _frog_.

The _wall_ is that portion of the hoof which we see when the foot rests
on the ground. It is a plate of horn which, applied to the anterior and
lateral surfaces of the foot, diminishes in height as it approaches the
posterior part of the region. Posteriorly and at each side the wall is
folded on itself, and is then directed forwards to terminate in a point,
after having enclosed the frog, which we will soon study.

[Illustration: FIG. 97.--LEFT ANTERIOR FOOT OF THE HORSE: ANTERIOR
ASPECT.

1, Outer side; 2, inner side.]

Although the wall forms a continuous whole, it has been divided into
regions to which special names are given. The anterior part, from the
superior border to the inferior, is called the _pince_ or _toe_ for a
width of 4 to 5 centimetres. External to the toe, and on each side of
it, for a distance of 3 or 4 centimetres, is the _nipple_. Behind the
_nipples_ are the _quarters_. Still further back, where the wall folds
on itself, forming the _buttress_, is found the region of the _heels_.
Finally, the portions of the wall which form its continuation in passing
forward are called the _bars_.[36] These are only visible on the
inferior surface of the hoof (see Fig. 100).

  [36] It is to the angle of inflexion or heel that some authors give
       the name of buttress; it is the bars which other authors
       designate in this fashion.

The wall, convex transversely, is, in its anterior part (viz., the
_toe_) inclined strongly downwards and forwards. This obliquity tends to
become gradually effaced on the lateral parts to such a degree that at
the quarters it becomes almost perpendicular to the surface of the
ground.

The internal quarter is less rounded than the external; in addition to
this (Fig. 97), it approaches more nearly to the vertical direction.

[Illustration: FIG. 98.--LEFT ANTERIOR FOOT OF THE HORSE: EXTERNAL
ASPECT.

1, Fetlock; 2, spur or beard; 3, pastern; 4, outline determined by the
external fibro-cartilage; 5, acute angle; 6, nipple; 7, quarter; 8,
heel.]

In our opinion, this latter difference clearly recalls certain
characters of the general form of the human foot. In fact, the latter
has its dorsal surface inclined downwards and outwards, whereas its
internal border may be said rather to be vertical. A transverse section
of the foot (Fig. 99) justifies this comparison, which to us appears
interesting, not only as regards the resemblance which exists between
these organs of support, but, further, because it constitutes a mnemonic
which enables us, on condition that we remember the form of the human
foot, to recall the above-described character of that of the horse.

The greater convexity of the outer portion of the hoof is found equally
on the human foot; the external border of this foot is more convex than
the opposite one.

The inferior border of the wall (Fig. 100) is, in the case of unshod
horses, always in wear when in contact with the ground. It is intimately
united to the circumference of the sole (see further on).

[Illustration: FIG. 99.--VERTICAL AND TRANSVERSE SECTION OF A LEFT HUMAN
FOOT: OUTLINE OF THE DIVIDED SURFACE OF THE POSTERIOR SEGMENT OF THIS
SECTION (DIAGRAMMATIC FIGURE).

AA´, Vertical axis passing through the middle of the leg and the second
toe; 1, outer side; 2, inner side.]

The superior border is hollowed on its internal surface by a groove, the
cutigerous cavity or basil, which lodges the cushion (see Fig. 95). We
have described this latter above, in connection with the flesh of the
foot.

The substance of the wall presents a fibrous appearance which is pretty
strongly pronounced. The constituent fibres from which this appearance
results are directed from the superior border towards the inferior in
parallel and regular lines.

The _sole_ is a horny plate which occupies the inferior surface of the
hoof (Fig. 100). It is situated between the inferior border of the wall
and the bars; and, on account of the oblique direction of these latter,
it presents a strongly-marked groove of a [V]-form, with the opening
directed backwards. In this depression is lodged the frog.

The inferior surface is concave, and thus forms a sort of vault, more or
less deep, according to the individual. The sole has a scaly, laminated
aspect.

We have seen (Fig. 93, and p. 249) that on the inferior surface of the
claws of carnivora is found a small interval which is filled by a plate
of a more friable horny substance, to which has been given the name of
the plantar nail. It seems to us that there is an interesting
relationship between the said plantar nail and the sole which we have
just been studying.

[Illustration: FIG. 100.--INFERIOR SURFACE OF A FORE-HOOF OF THE HORSE:
LEFT SIDE.

1, Internal border of the wall (toe); 2, wall; 3, quarter; 4, heel; 5,
bar; 6, sole; 7, frog; 8, median cavity; 9, prominence of the frog; 10,
lateral cavity.]

Indeed, these two horny structures appear to be homologous. Is not the
lamina of the claw comparable to the wall of the hoof? And does not the
interval which occurs at the inferior part of this latter, and is filled
by the sole, recall that which, in extremely reduced form, is filled by
the plantar portion of the claws?

The _frog_ (Fig. 100) is a mass of horn, in form of a wedge, with its
apex in front, which occupies the space limited laterally by the
recurved portions of the wall (the bars) and the posterior border of the
sole.

It covers the plantar cushion previously described (p. 252) and
reproduces its form.

Its inferior surface is hollowed out in the middle by an excavation,
which is known as the _median lacuna_. This cavity separates the
branches of the frog, which terminate posteriorly by two swellings which
are known as _the prominences of the frog_, forming two rounded
elevations situated above the claws. These same branches unite in front
of the median lacuna to form the body of the frog. This latter, in its
anterior part, gradually narrows, and terminates in a point which
occupies the bottom of the hollow limited laterally by the bars of the
wall and the posterior border of the sole.

Between the lateral surfaces of the frog and the bars are found two
angular cavities--_the lateral lacunæ_, or the _commissures of the
frog_.

[Illustration: FIG. 101.--THIRD PHALANX OF THE HORSE: LEFT ANTERIOR
LIMB, INFERIOR VIEW.

1, External border; 2, internal border; 3, semilunar crest; 4, 4,
re-entrant processes.]

[Illustration: FIG. 102.--THIRD PHALANX OF THE HORSE: LEFT POSTERIOR
LIMB, INFERIOR VIEW.

1, External border; 2, internal border; 3, semilunar crest; 4, 4,
re-entrant processes.]

As an indispensable complement to the study which we have just
made, it is necessary to add that the hoofs of the fore-limbs and
those of the hind ones present differences of form which cannot be
ignored--differences which we are already able to conjecture by looking
at the respective third phalanges which terminate those limbs, and
especially at their inferior surfaces (Figs. 101, 102).

The hoofs of the fore-limbs (see Fig. 100), viewed on their plantar
surface, are more rounded than those of the hind-limbs (Fig. 103)--so
that their external contour may be compared to a semicircle--whilst the
hind-hoofs, which are narrow and of more oval shape, rather recall by
their form the aspect of an ogive.

This seems to result from the fact that the fore-limbs support the more
considerable part of the weight of the animal. The best proof which can
be given of this overweighting is the eagerness with which very often,
when a horse is stopped near the edge of a footpath, for example, he
places his fore-feet on the latter. In thus raising his fore-quarters,
he throws part of his weight backwards, and in this way relieves his
fore-limbs.

[Illustration: FIG. 103.--INFERIOR SURFACE OF A HIND-HOOF OF A HORSE:
LEFT SIDE.

1, External border; 2, internal border.]

With regard to the difference of form which we have just pointed out, we
have sometimes heard the following comparison made: the contour of the
hoofs of the fore-limbs, viewed from below, recalls that of an apple;
that of the hoofs of the hind-limbs recalls the outline of a pear.

As a mnemonic this comparison is insufficient, for nothing connects
either of the forms indicated with the region to which the hoofs belong.

We much prefer one made for us this very year by one of the students of
our course at the School of Fine Arts, after the lecture in which we had
just pointed out the differences in question. Giving the idea of a
semicircle and an ogive, which we described above, he remarked to us
that the idea would perhaps be more easily fixed in the memory if we
associated with it the idea of the chronological order in which the
Roman and ogival art succeeded. Indeed, as the Roman art preceded the
ogival art, so the hoofs which have the semicircular form precede those
which have the form of an ogive.

This interpretation appeared to us ingenious; this is why we wished to
give it here a place which seems to us to be merited.

[Illustration: FIG. 104.--LEFT POSTERIOR FOOT OF A HORSE: EXTERNAL
ASPECT.]

The wall of the hoof of a fore-limb, viewed on one of its lateral
surfaces (see Fig. 98), is more oblique than that of one of the
hind-hoofs looked at in the same way (Fig. 104). This difference, very
marked especially at the region of the toe, is correlated with that of
the direction of the pastern. In fact, in the anterior limbs this is a
little more oblique than in the opposite ones.

We have still to describe, in connection with the horse, some epidermic
tissues, which are known as _chestnuts_.

The chestnut is a small, horny plate which is found on the internal
surface of each of the limbs, at a level differing on the anterior from
that of the posterior ones.

On the anterior limbs the chestnut is situated on the internal surface
of the forearm, towards the middle part, or the inferior third of this
region. On the posterior limbs it is developed on the back of the
superior extremity of the internal surface of the canon, towards the
inferior part of the ham--that is, the tarsus.

[Illustration: FIG. 105.--FOOT OF THE OX: LEFT SIDE, ANTERO-EXTERNAL
VIEW.

1, Internal hoof; 2, external hoof; 3, internal surface of this latter;
4, internal spur.]

Inasmuch as some authors consider the chestnuts as being vestiges of the
thumb and the great-toe, we propose giving a mnemonic which will enable
us to remember their situation, or, rather, their difference of level.

If we consider that the thumb, in the human species, is longer than the
first toe, we may easily remember that the chestnut is placed higher in
the anterior limbs than in the posterior ones. Indeed, if we suppose a
digit taking its origin at these points, it will be longer in front (the
thumb) than behind (the first toe).

=Hoofs of the Ox and the Pig.=--The ox has four hoofs on each foot--two
which contain the third phalanges, and two others, rudimentary, situated
at the posterior aspect of the limb, at the level of the inferior part
of the canon; these latter bear the name of _spurs_. We will occupy
ourselves especially with the former (Fig. 105).

Each of the hoofs presents three faces which, if we consider them in
relation to the median axis of the limb to which they belong, are:
external, internal, and inferior. The external surface resembles the
wall of the hoof of the horse. The internal surface is slightly concave
from before backwards, so that the external and internal hoofs of the
same foot are not in contact with each other, except by the extremities
of this surface, and that an interval separates them between these two
points. The inferior surface, slightly depressed, ends behind in a
swelling produced by the plantar cushion, which covers a thin lamina of
horn.

At the anterior part of the hoof these three surfaces unite in forming a
well-marked angle which, on account of the concavity of the internal
surface, is slightly curved towards the axis of the foot.

The pig has also four hoofs--two for the great digits and two for the
lateral digits. They recall those of the ox.




CHAPTER IV

PROPORTIONS


Inasmuch as we have taken for granted, in connection with the present
volume, that before entering on the study of the anatomy of quadrupeds
the reader was prepared for it by a sufficient knowledge of human
anatomy, it is quite natural that we should extend the same supposition
to the study of proportions.

For this reason, the definition of proportions, considered from a
general point of view, their signification, their function and their
utility, are questions which it would be superfluous to enter upon here.
We will content ourselves by calling to mind that the common measure
chosen by preference is the length of the head, and that, ordinarily, it
is with it that we compare the dimensions of other parts.

Among the animals whose structure we have examined, there is one of
which the proportions deserve to be marked in preference to every other:
this is the horse.

Wherefore this preference? In the first place, it is because of the
overwhelming position which this animal occupies in the artistic
representation of quadrupeds; that it is more frequently associated with
man; that, notwithstanding its division into different races, its
general proportions may be referred to a special type.

It is also because the indications relative to these proportions will
suffice to show the way which the artist must follow in order to find
for himself, at the time when the necessity for it arises, the
proportions which characterize the other animals.

Our intention is not, in connection with the subject which now occupies
us, to enter into a deep discussion on the various opinions which have
been set forth. We desire, above all, to give some indications which,
from the practical point of view, can be utilized in the representation
of the horse, and at the beginning to demonstrate the advantages of
these indications. Now, there is a fact which we have had occasion to
note; it is the following: almost invariably, when a person who is
little accustomed to represent the horse, or not previously informed of
certain proportions of lengths, begins to draw from nature, the error
generally committed is that of making the head too small and the body
too long. Is it a preconceived idea which is the cause that one regards
them in this manner? Perhaps. At all events, certain artists who have
made the representation of horses their special study have even had this
habit. It is therefore necessary to be informed of the proportions; this
is the object of the study which we are now undertaking.

Bourgelat,[37] in the eighteenth century, fixed for the first time and
in complete fashion the proportions of the horse; it is he,
consequently, who created the æsthetics of the horse. It is but justice
to recall the fact. His system has a point of analogy with that which is
employed to determine the human proportions. Indeed, Bourgelat chose the
length of the head as a standard of measurement, and the subdivisions of
the head for measures of less extent. 'Since beauty,' said he,[38]
'resides in the congruity and proportion of the parts, it is absolutely
necessary to observe the dimensions, individual and relative, and in
order to acquire a knowledge of the proportions, to assume a kind of
measure which can be indiscriminately common for all horses. The part
which can serve as a standard of proportion for all the others is the
head. Take a measurement between two parallel lines--one tangent to the
nape of the neck or the summit of the forelock, the other tangent to
the extremity of the anterior lip--a line perpendicular to these two
tangents will give you its geometrical length. Divide this length into
three portions, and give to these three parts a special name, which may
be applied indefinitely to all heads--as, for example, that of _prime_.
Any head whatsoever will, accordingly, in its geometrical length, always
have three _primes_; but all the parts which you will have to consider,
whether in their length, in their height, or in their width, cannot
constantly have either one prime, or a prime and a half, or three
primes; subdivide, then, each _prime_ into three equal parts, which you
will name _seconds_, and as this subdivision will not suffice to give
you a just measure of all the parts, subdivide anew each _second_ into
twenty-four _points_, so that a head divided into three _primes_ will
have, by the second division, nine _seconds_, and two hundred and
sixteen _points_ by the last.'

  [37] Claude Bourgelat, founder of the veterinary schools in France. He
       was born at Lyons in 1712, and died at Paris in 1779.

  [38] Bourgelat, 'Éléments de l'art vétérinaire. Traité de la
       conformation extérieure du cheval,' Paris, edition of 1785, p.
       133.

But where this system appears to us to have lost somewhat of its unity
is when the author transforms it, in pointing out the following mode of
procedure: 'But the head itself may err by default of proportion. This
part is not, indeed, considered as either too short or too long, too
thin or too thick, but by comparison with the body of the animal. Now,
the body, being required to have--whether in length, reckoning from the
point of the arm to the prominence of the buttock, or in height,
reckoning from the summit of the withers to the ground--two heads and a
half; whenever the head, by its geometrical length, shall give, in
length or in height, to the body measured more than two and a half times
its own length, it will be too short; and if it gives less, it will be
too long.

'In the case in which one of these faults exists there would be no
further question of establishing by its geometrical length the
proportions of the other parts. Give up this common measure, and measure
the height or the length of the body; divide the length or the height
into five equal portions; take, then, two of these divisions, divide
them into _primes_, _seconds_, and _points_, corresponding to the
divisions and subdivisions which you would have made of the head, and
you will have a common measure, such as the head would have given you if
it had been proportionate.'[39]

  [39] Bourgelat, _loc. cit._, p. 135.

[Illustration: FIG. 106.--THE PROPORTIONS OF THE HORSE (AFTER
BOURGELAT).

_To face p. 265._]

We understand, up to a certain point, that Bourgelat may have been able
to give this advice which, generally speaking, is sufficiently
practical, since, in certain cases, he was able to pronounce that such a
head was too small or too large. But it is always mischievous, with
regard to the effect produced on the reader, to propose to him, in the
application of a rule, to suppress the foundation on which this rule is
established. Besides, even if all the measurements compared with the
two-fifths of the length of the body are proportionate with regard to
one another, the animal, in spite of this, since the head must be taken
into consideration, will, in a strict sense, be none the less
disproportioned.

The proportions given by Bourgelat are as follows[40] (Fig. 106):

  [40] _Ibid._, p. 136, and onward.

1. =Three geometrical lengths of the head= give:

_The full height_ of the horse, reckoned from the forelock to the ground
on which he rests, provided that the head be well placed.[41]

  [41] By 'the head being well placed,' Bourgelat means 'vertically
       posed,' the outline of the forehead then coinciding with a
       vertical line, which at the other end touches the anterior
       portion of the nose.

2. =Two heads and a half= (B)[42] equals:

  [42] The letters in parentheses relate to the corresponding measures
       marked by the same letters on the third diagram of Fig. 106.

_The height of the body_ from the summit of the withers to the ground.

_The length of the same body_, those of the forehand and of the
hind-quarter taken as a whole from the point of the arm to the point of
the buttock inclusive.

3. =An entire head= (A) gives:

_The length of the forepart_ from the summit of the withers to the
termination of the neck.

_The height of the shoulders_ from the summit of the elbow to the top of
the withers.

_The thickness of the body_ from the middle of the belly to the middle
of the back.

_The width_ from one side to the other.

4. =A head measured from the top of the forelock to the commissure of
the lips= (C). This measurement slightly curtailed, unless the mouth is
very deeply cleft, equals:

_The length of the crupper_, taken from the superior point of the
anterior angle of the ilium to the tuberosity of the ischium, forming
the point of the buttock.

_The width of the crupper or of the haunches_, taken from the inferior
points of the angles of the ilia.

_The height of the crupper_, viewed laterally, taken from the summit of
the posterior angles of the ilia to the point of the patella, the leg
being in a state of rest.

_The lateral measure of the posterior limb_, from the point of the
patella, to the lateral and salient part of the ham, to the right of the
articulation of the tibia with the trochlea.

_The perpendicular height of the articulation above named_ above the
ground.

_The distance from the point of the arm_ to the angle formed by the
junction of the head and neck.

_The distance from the summit of the withers_ to the junction of the
neck with the thorax.

5. =Twice this last measure= (C)[43] gives almost:

  [43] The proportions given in the two paragraphs 6 and 7 are, under
       another form, the same as those pointed out in paragraph 2, with
       this difference, that in this latter they are more clearly
       expressed.

_The distance of the summit of the withers_ to the tip of the patella.

_The distance of the point of the elbow_ to the summit of the crupper or
the posterior angles of the ilia.

6. =Three times this measure, plus a half-width of the pastern, the
equivalent of two heads and a half=, will give:

_The height of the body_, taken from the top of the withers to the
ground.

_Its length_, taken from the point of the arm to the point of the
buttock inclusive.

7. =This same measure, plus the entire width of the pastern=, gives:

_The total length of the body_, taken accurately.

8. =Two-thirds the length of the head= (D) will equal:

_The width of the chest_, from the tip of one arm to that of the other,
from outside to outside.

_The horizontal measurement of the crupper_ taken between two verticals,
of which one forms a tangent to the buttock, and the other passes
through the summit of the crupper and touches the tip of the patella.

_The third of the length of the hind-quarter and of the body_ taken
together, as far as the vertical from the withers, touching the elbow.

_The anterior length of the hind-limb_, taken from the tuberosity of the
tibia to the fold of the ham.

9. =One-half of the length of the head= (E) is the same as:

_The horizontal distance from the tip of the arm_ to the vertical line
from the summit of the withers and touching the elbow.

_The width of the neck_, viewed laterally, taken from its insertion in
the trough of the jaw to the roots of the first hairs of the mane, on a
line which forms with the superior contour two equal angles.

10. =One-third of the entire length of the head= (F) gives:

_The height of its superior part_ from the summit of the forelock to a
line which passes through the most salient points of the orbits.

_The width of the head_ below the lower eyelids.

_The lateral width of the forearm_, taken from its anterior origin to
the point of the elbow.

11. =Two-thirds of this length=[44] (G) gives:

  [44] That is to say, two-ninths of the whole length of the head.

_The distance of the point of the elbow_ above the plane of the lower
surface of the sternum.

_The depression of the back_ in relation to the summit of the withers.

_The lateral width of the posterior limbs near the hams._

_The space or distance of the forearms from one ars_[45] to the
opposite.

  [45] We call the region where the superior and internal part of the
       forearm is joined to the trunk the 'ars.' The space between the
       ars of one side and the ars of the opposite side is called the
       'inter-ars.'

12. =One-half of the third of the entire length of the head=[46] (H)
equals:

  [46] That is to say, one-sixth of the total length of the head.

_The thickness of the forearm_, viewed from the front, and taken
horizontally from the ars to its external surface.

_The width of the crown of the fore-feet_ whether from one side to the
other, or from before backwards.

_The width of the crown of the hind-feet_, from one side to the other
only.

_The width of the posterior fetlocks_, taken from the front to the
origin of the spur.

_The width of the knee_ seen from the front. Note: this measure is a
little too large.

_The thickness of the ham._ Note: this measure is a little under the
mark.

13. =One-fourth of the third of the length of the head=[47] (I) gives:

  [47] That is, one-twelfth of the length of the head.

_The thickness of the canon of the fore-limb_: that of the hind-quarter
is a little thicker.

14. =One-third of this same measure=[48] (K) equals:

  [48] That is, a ninth of the length of the head.

_The thickness of the fore-limb close to the knee_ in its narrowest
part.

_The thickness of the posterior pasterns_, viewed laterally.

15. =The height from the elbow to the fold of the knee= (L) is the same
as:

_The height from this same fold to the earth._

_The height from the patella to the fold of the ham._

_The height from the fold of the ham to the crown._

16. =The sixth part of this measure= (M) gives:

_The width of the canon of the fore-limb_, viewed laterally, in the
middle of its length.

_The fetlock_, viewed from the front.

17. =The third of this same measure= (N) is very nearly equal to:

_The width of the ham_, from the fold to the point.

18. =A fourth of this measure= (O) gives:

_The width of the knee_, measured laterally.

_The length of the knee._

19. =The interval between the eyes from one great angle to the other=
(P) equals:

_The width of the hind-leg_, viewed laterally, from the cleft of the
buttocks to the inferior part of the tuberosity of the tibia.

20. =One-half of this interval between the eyes= (1/2 P) gives:

_The width of the posterior canon-bone_, viewed laterally.

_The width of the fetlock of the fore-limb_, from its anterior summit to
the root of the spur.

Finally, the difference of the height of the crupper with respect to the
summit of the withers.

It is certain that the multiplicity of these proportions, and above all
the exaggeration of details into which Bourgelat fell in indicating
certain of the measures which constitute the bases of some of them, may
repel the reader.

For this cause we desire to add to the preceding, and also because the
question which we are treating would be incomplete without it, the
results obtained and published by other more modern authors, and in
particular by Colonel Duhousset.[49]

  [49] E. Duhousset, 'Le Cheval,' Paris, 1881.

This author, one of whose constant occupations is the measurement of the
different regions of the horse, has the incontestable merit of having
drawn attention to this question, and of having strained all his
energies in the propagation of the knowledge which until then was little
diffused. Among the proportions which he recommends, there are some
which are the result of his own observations; whilst others, which he
has verified and adopted, are the result of a judicious selection of
those given by Bourgelat, which we have just reproduced in the preceding
pages.

We join thereto also certain indications furnished by MM. A. Goubeaux
and G. Barrier,[50] distinguishing these latter by the initials (G. and
B.) of their authors (Fig. 107).

  [50] Armand Goubeaux and Gustave Barrier, 'De l'extérieure du Cheval,'
       Paris, 1882.

=The length of the head almost exactly equals=:

1. Depth from the back to the belly, N, O,[51] the thickness of the
body.[52]

  [51] Look for the points indicated by these letters on Fig. 107, which
       is related to the proportions which are here discussed.

  [52] The proportion previously indicated by Bourgelat (see p. 265,
       paragraph 3).

2. From the summit of the withers to the point of the arm, H, E.

3. From the superior fold of the stifle to the point of the ham, J´, J.

4. From the point of the ham to the ground, J, K.

5. From the dorsal angle of the scapula to the point of the haunch, D,
D.

[Illustration: FIG. 107.--PROPORTIONS OF THE HORSE (AFTER COLONEL
DUHOUSSET).]

6. From the passage of the girth to the fetlock, M, I, or higher in
large horses and racers; to the middle of the fetlock or lower for small
ones and those of medium size.

7. From the superior fold of the stifle to the summit of the crupper in
those specimens whose coxo-femoral angle is very open. This distance is
always much less in others (G. and B.).[53]

  [53] A proportion relative to the same region, and which at the outset
       might appear similar, is pointed out by Bourgelat (see p. 266,
       paragraph 4). But there exists a difference, for Bourgelat
       compared the length of the head, measured from the forelock to
       the commissure of the lips, and not that of the entire head, to
       the distance which separates the summit of the rump and the tip
       of the patella.

=Two and a half times the length of the head= gives:

1. The height of the withers, H, above the ground.[54]

  [54] This proportion is that given by Bourgelat (see p. 265, paragraph
       2).

2. The height of the summit of the crupper above the ground.[55]

  [55] Consequently the withers and the crupper, being the same height,
       are situated on the same horizontal plane. Bourgelat, on the
       contrary, points out a difference of level in connection with
       these regions. According to him the summit of the crupper is
       situated below the horizontal plane passing the withers, and this
       distance equals half of the space which separates the great angle
       of one eye from that of the other (see p. 269, paragraph 20).

3. Very often the length of the body, from the point of the arm to that
of the buttock, although for a long time the type of Bourgelat had been
set aside as a conventional model, short and massive.[56]

  [56] See p. 265, paragraph 2.

And M. Duhousset adds to this:

'The drawing that we offer, which has two heads and a half in height and
length, is that of a horse which we frequently meet with' (see Fig. 107;
see also p. 279, where we again consider this question of the length of
the body of the horse).

'The crupper, from the point of the haunch to that of the buttock, D, F,
is always less than that of the head. This difference varies from 5 to
10 centimetres. The width of the crupper, from one haunch to the other,
often very slightly exceeds its length.' MM. Goubeaux and Barrier add
that frequently it equals it.[57]

  [57] If we refer to the proportions indicated by Bourgelat, we shall
       find that the proportions relative to the crupper are also
       indicated there (see p. 266, paragraph 4).

'The crupper, such as we have just defined it, D, H, may also be found
to a fair degree of exactness, as regards length, four times on the same
horse.'

1. From the point of the buttock to the inferior part of the stifle, F,
P.

2. The width of the neck, a little in front of the withers to a little
above the point of the arm, S, X.[58]

  [58] MM. Goubeaux and Barrier replace this by the following: 'The
       width of neck at its inferior attachment from its insertion into
       the chest to the origin of the withers, S, X.' Bourgelat
       discovered the same proportion (see p. 266, last line of
       paragraph 4).

3. From this latter point to below the lower jaw, X, Q, when the head is
naturally placed parallel to the shoulders, E, H.[59]

  [59] MM. Goubeaux and Barrier replace this by the following: 'From the
       insertion of the neck into the chest to the lower border of the
       lower jaw, X, Q, when the head is parallel to the shoulder.'

4. From the nape to the nostrils, _n, n´_.[60]

  [60] MM. Goubeaux and Barrier add: 'Or to the commissure of the lips.'
       It is thus, besides, that Bourgelat measured the head for
       comparison with the crupper (see p. 266, paragraph 4).

The measure of =half of the head= also acts as a good guide for the
construction of the horse, when we know that it frequently applies to
many of the parts--to wit:

1. From the forehead above the eyes, perpendicular to the line which is
tangent to the lower jaw, P, Q.

2. Outline of the neck at the level of the base of the head, Q, L.[61]

  [61] Proportion indicated by Bourgelat (see p. 267, paragraph 9).

3. From the crown of the fore-foot to below the knee, T, T´.

4. In the legs, from the base of the fetlock to that of the ham, U, V.

5. Finally, it is nearly of the length of the humerus from the point E
to the radius.[62]

  [62] MM. Goubeaux and Barrier replace these by the following:

       1. 'From the most prominent part of the lower jaw to the profile
       of the forehead above the eye, P, Q (thickness of the head).

       2. 'From the throat to the superior border of the neck behind the
       nape, Q, L (attachment of the head).

       3. 'From the inferior part of the knee to the crown, T, T´.

       4. 'From the base of the ham to the fetlock, U, V.

       5. 'Finally, from the point of the arm to the articulation of the
       elbow (approximate length of the arm).'


PROPORTIONS OF THE HEAD OF THE HORSE[63]

  [63] Extract from the work of MM. Goubeaux and Barrier on the exterior
       of the horse. As before, the initials G. and B. of these authors
       are added.

Although it is very difficult, says M. Duhousset, when we speak of
measurements taken on the living animal, to formulate other than
approximations, we believe we have determined with sufficient accuracy
the following results, which are the outcome of our numerous
observations. The head which we present is that of a horse which we have
frequently come across as a mean term between the highly bred and the
draught horse. Under this heading, it will not be devoid of interest to
accompany with dimensions the two drawings to which are consigned the
measurements in question.

=Head viewed in Profile= (Fig. 108).--Length, A, B, from the nape to the
margin of the lips, 0·60 metre.

Thickness, C, D, from the angle of the lower jaw to the anterior surface
(a half-head), 0·30 metre. This line passes through the middle of the
eye, taken perpendicularly, to the profile of the anterior surface. Many
common horses present it, especially the heavier draught horses; in
finely-bred subjects it is a little shorter (G. and B.).

Depth, I, H, of the neck in its narrowest part (a half-head), 0·30
metre. It is frequently greater; this is noticeable in all instances
where the superior parts of the neck are deficient in fineness. It is
this which we see in draught horses, and in those which become too
fleshy (G. and B.).

Distance, O, R, of the internal commissure of the eye from the superior
border of the commissure of the nostril (G. and B.) (a half-head), 0·30
metre. It is more considerable on the common head, and on that which is
too long.

Distance, A, O, from the nape to the internal angle of the eye, 0·22
metre. This distance is equivalent to the thickness of the head, P, Q,
taken perpendicularly from the profile of the anterior surface, and
passing at the level of the maxillary fissure and spine.

It is, again, equal to Q, O, from the internal angle of the eye to the
maxillary fissure; and to P, G, from the middle of the face to the
commissure of the lips (G. and B.).

The distance, P, E, from the middle of the face to the maxillary spine
is about the sixth of the total length of the head--0·10 metre.

[Illustration: FIG. 108.--PROPORTIONS OF THE HEAD OF THE HORSE, VIEWED
IN PROFILE (AFTER COLONEL DUHOUSSET).]

The line B, E, reckoned from the extremity of the lips to the maxillary
spine, is equal:

To E, F, from the maxillary spine to the external auditory meatus, to be
seen only on the skull;

To H, G, from the insertion of the neck in the trough to the commissure
of the lips (G. and B.);

To Q, R, from the maxillary fissure to the superior commissure of the
nostril (G. and B.);

To Q, B, from the fissure of the maxilla to the border of the lips (G.
and B.);

To O, D, from the internal angle of the eye to the angle of the lower
jaw, provided that the line C, D be in proportion (G. and B.).

[Illustration: FIG. 109.--THE SAME DESIGN AS THAT OF FIG. 108, ON WHICH
WE HAVE INDICATED, BY SIMILAR LINES, THE PRINCIPAL CORRESPONDING
MEASUREMENTS.

Half the length of the head, and the dimensions which equal it; distance
which separate the nape from the internal angle of the eye, and the
dimensions which equal it; distance which separates the internal angle
of the eye from the border of the lips, and the dimensions which equal
it.[64]]

  [64] It is thus that in our teaching, but by means of lines of
       different colours, we present the proportions reproduced in Fig.
       108. Experience has demonstrated to us that this replacement of
       letters by conventional lines renders the proportions more easily
       appreciable, and that these lines, striking the eye more
       forcibly, then impress themselves better on the memory. Fig. 111
       bears the same relation to Fig. 110.

Finally, very frequently to O, H, from the internal angle of the eye to
the insertion of the throat into the maxillary trough (G. and B.).

An equality still more frequent is that which exists between the
distances:

O, B, from the internal angle of the eye to the margin of the lips;

A, H, from the nape to the insertion of the throat into the maxillary
trough;

And H, B, from this latter point to the margins of the lips.

[Illustration: FIG. 110.--PROPORTIONS OF THE HEAD OF THE HORSE, SEEN
FROM THE FRONT (AFTER COLONEL DUHOUSSET).]

=The Head, Front View= (Fig. 110).--If, to continue our examination,
adds M. Duhousset, we regard the head from the front, we find its
greatest width at A, B, the extreme points of the orbital arches.

This width is 22 centimetres.

It is again equal to:

A, C, from one arch to the nape;

A, D, from one arch to the middle of the face.

D, E, from the middle of the face to the margin of the lips.

From the auditory canal, G, to the maxillary spine, F, is the same
distance as from this point to the margins of the lips, E, or, better,
to the end of the teeth.

[Illustration: FIG. 111.--THE SAME FIGURE AS FIG. 110, ON WHICH WE HAVE
MARKED BY SIMILAR LINES THE PRINCIPAL MEASUREMENTS WHICH CORRESPOND
THERETO.

Distance which separates one of the orbital arches from that of the
opposite side, and the dimensions which equal it; distance which
separates the auditory meatus from the maxillary spine, and the
dimensions which equal it; distance which separates one maxillary spine
from that of the opposite side, and the dimensions which equal it;
distance which separates the lip of one side from that of the opposite,
and the dimensions which equal it.[65]]

  [65] See the note relative to Fig. 109.

The line G, C, from the auditory meatus to the nape, is equal to the
sixth of the head, 10 centimetres; the line A, G, from the orbital arch
to the auditory meatus, is a little longer, and measures 12
centimetres.

The distance F, I, comprised between the maxillary spines, is 18
centimetres.

It is equal to:

O, O, the distance between the internal angles of the eyes (G. and B.);

F, R, the distance from the maxillary spine to the superior commissure
of the corresponding nostril (G. and. B.);

F, P, from the maxillary spine to the _salt-cellar_.[66]

  [66] We designate under the name _salt-cellar_ a depression situated
       external to the frontal region and above the eye.

From the nape to the internal angle of the eye, C, O, is the same
distance as from this latter point to the commissure of the lips, O, T;
and from the maxillary spine to the upper lip F, S (G. and B.).

The distance apart, T, T, of the two commissures of the lips gives, very
nearly, the distance from the superior border of the orbital arch to the
base of the ear or the auditory meatus. In the state of rest, the outer
limit of the separation of the nostrils does not exceed the width of the
knee;[67] we frequently find the same distance intercepted above the
nape by the tranquil ears. In the figure (Fig. 110) we have
intentionally represented them directed in a different plane, in order
to show that when the pinna is turned backward, it none the less
preserves the contour of bracket form, more or less pronounced according
to the breeding of the subject, and characterizing in repose the
interior curves of the ear.

  [67] We remind our readers that the name 'knee' is given by
       veterinarians to the region occupied by the carpus.

The extreme limit of the lips, M, N, but very slightly exceeds that of
the nostrils; on many heads of harmonious proportions this distance is
found to be the half of A, B.

In order not to interrupt the course of the preceding exposition, we
decided to withhold till afterwards some reflections which have been
suggested to us by certain of the proportions which are there indicated.
The proportions in question are important--we may even say that they are
fundamental, for they have for object the relation which exists between
the length of the head, the height of the body, and the length of the
latter.

We have already seen that, according to Bourgelat, the length of the
head is contained two and a half times in the length of the body, from
the point of the arm to the point of the buttock; and, also, two and a
half times in the height measured from the apex of the withers to the
ground (see p. 265). We saw afterwards that M. Duhousset, having adopted
these proportions, pointed out, further, that the same dimension was
again found equally to exist from the summit of the crupper to the
ground--a height which Bourgelat considered as being of less extent.
There results, then, from the latter proportions, which we have just
recalled, this interesting fact: that they simplify very much, from the
point of view of design, the placing in position of the horse, on the
condition always that this latter be always viewed directly on one of
its lateral aspects.

[Illustration: FIG. 112.--HORSE OF WHICH THE LENGTH CONTAINS MORE THAN
TWO AND A HALF TIMES THAT OF THE HEAD, AND OF WHICH THIS DIMENSION (A,
B) EXCEEDS THE HEIGHT.]

Indeed, in this case, if we except the neck and the head, the body,
inasmuch as its height and its length are equal, may be inscribed in a
square, of which one of the sides corresponds to the withers and to the
summit of the crupper, two of the other sides to the point of the arm
and to that of the buttock the fourth being represented by the ground.
This is simple, but this simplicity even has its inconveniences.

It follows that this proportion, thus expressed, seems to exclude from
every artistic representation certain categories of horses, which upon
the whole might be regarded as beautiful, and the existence of which in
any case it would be a pity not to indicate.

[Illustration: FIG. 113.--HORSE OF WHICH THE LENGTH CONTAINS MORE THAN
TWO AND A HALF TIMES THAT OF THE HEAD, AND OF WHICH THIS DIMENSION (A,
B) EXCEEDS THE HEIGHT.]

Let us examine at the outset that which is relative to the length of the
body, equal to two and a half times the length of the head. This
proportion is sometimes met with, and therefore may be considered exact;
but it is necessary to add that its existence is not discoverable in the
majority of cases. That for some authors it constitutes a perfect model
we will not gainsay, but it is our impression that, when it exists, the
head appears a little large, or, more exactly, the body a little short.

Without attaining exactly to three times the length of the head, as some
authors (Saint-Bel, Vallon) have announced, the body of the horse,
nevertheless, measured as is stated above, frequently contains it more
than two and a half times. We give in support of this some outline
reproductions, executed after photographs (Figs. 112, 113, 114).

There still remains the question regarding the equality of the height
and of the length of the body of the horse.

This equality, after the proportions previously indicated, would seem
bound to appear in all the cases observed. Now, if we measure the
examples reproduced in Figs. 112, 113, and 114, we shall see that
sometimes the two dimensions are unequal, the height being greater than
the length, or inversely.

[Illustration: FIG. 114.--HORSE OF WHICH THE LENGTH CONTAINS MORE THAN
TWO AND A HALF TIMES THAT OF THE HEAD, AND OF WHICH THIS DIMENSION (A,
B) IS INFERIOR TO THE HEIGHT.]

It is the same, if we examine a certain number of specimens; we are able
to determine that the proportion chosen in preference by authors is not
exactly that which is oftenest met with. It will, very probably, be
objected that it is so for the most beautiful types, and that the
indifferent ones are generally the more numerous. The essential thing
would be to know, above all, if the type of two heads and a half of
length and of height is really the only beautiful one. However that may
be, of the fifty African horses measured by M. Duhousset, only fourteen
possessed the equality indicated; twenty-six were less long than high,
and ten more long than high.[68]

  [68] E. Duhousset, 'The Horse,' Paris, 1881.




CHAPTER V

THE PACES OF THE HORSE


As a completion of the studies we have just been making, some notions
relative to the paces of the horse seem to us to be absolutely
indicated.

Let it be permitted to us to remind the reader in this connection that
we have already been for twenty-one years occupied with this question,
and that by means of an articulated figure, a sort of movable mannikin,
we have endeavoured to demonstrate to artists the differences which
characterize the various paces of the horse.[69] The arrangement then
employed cannot, evidently, be used in the present volume, but we will
inspire ourselves, in the preparation of the present chapter, with the
elements of demonstration which we have employed, and which, in the
course of our teaching, we have had the satisfaction of seeing
favourably received.

  [69] Édouard Cuyer, 'Les Allures du Cheval,' demonstrated with the aid
       of a coloured, separable, and articulated table, Paris, 1883.

       This table was the subject of a note communicated to the Academy
       of Sciences by Professor Marey ('Comptes rendus de l'Académie de
       Sciences') at the meeting of June 26, 1882. On the other hand, it
       has been the subject of a presentation which we have had the
       honour of being permitted to make to the Academy of Fine Arts at
       the meeting of November 4, 1882.

       The fasciculus in question has been since united with a more
       complete whole as regards the study of the horse. E. Cuyer and E.
       Alex, 'Le Cheval: Extérieur, Structure et Fonctions, Races,' avec
       26 planches coloriées, découpées et superposées, Paris, 1886.

The progressive movements by which an individual transports himself
from one place to another do not operate according to a unique method
and with a constantly uniform velocity. These various modes of
progression are designated under the name of _paces_.

It is extremely difficult to analyze, by simple observation, the
movements which characterize these gaits. Let us, for example, examine
the displacements made by the limbs of a horse during that of walking;
if we have no notion of these displacements, it will be, so to speak,
impossible to determine in what order they are executed. The sight of
the imprints left on the ground by the hoofs is not a sufficient means
of demonstration, especially for artists. The noise made by the blows of
these limbs, or by the little bells of different timbre suspended from
them, are absolutely in the same case.

Processes enabling us to fix or to register the paces are in every way
preferable. Such really exist; they are: instantaneous photography and
those which constitute the graphic method of Professor Marey. The
results given by the photograph are certainly appreciable; but, from the
didactic point of view, we give the preference to the graphic method,
the general characters and the mode of application of which we now
proceed to analyze.[70]

  [70] We cannot too strongly recommend the reading of the excellent
       works which Professor Marey has published, and which have for
       their object the study of movements, as well as the exhibition of
       the procedures which he has employed. E. J. Marey, 'La Machine
       Animale,' Paris, 1873; 'La Méthode graphique dans les Sciences
       expérimentales,' Paris, 1884; 'Le Vol des Oiseaux,' Paris, 1890;
       'Le Mouvement,' Paris, 1894.

It is necessary to understand first of all, in this connection, that
which relates to a man's walking pace.

The method of Professor Marey rests on the following principle: Suppose
two rubber globes connected with one another by a tube. If we compress
one of these globes, the air which it contains will be driven into the
other, and will afterwards return when the pressure has ceased. Nothing
more simple, evidently; but it is necessary to describe it in detail in
order the better to comprehend that which follows: The walker who is the
subject of experiment is furnished with special shoes (Fig. 115), having
thick indiarubber soles, hollowed in the interior, so that the whole
thus constituted forms a sort of hollow cushion which is compressed
under the influence of the pressure of the foot on the ground. A tube
which is attached to a registering apparatus, which the person who is
walking carries in his hand, communicates with this cavity (Fig. 116).
This apparatus is formed of a metal drum, which is closed at its upper
part by a flexible membrane. Each time that one of the man's feet
presses on the ground, the air contained in the cavity of the sole of
the shoe is driven into the drum, which we have just mentioned, and the
flexible membrane of this drum is elevated. To this membrane is attached
a vertical rod which supports a horizontal style.

[Illustration: FIG. 115.--EXPERIMENTAL SHOES, INTENDED TO RECORD THE
PRESSURE OF THE FOOT ON THE GROUND.]

When the membrane, as we have just seen, is elevated, the style is
lifted, and then descends when the pressure of the foot ceases. It
traces these displacements on a leaf of paper, the surface of which is
covered with a thin layer of lamp-black, which it removes by its
contact; different parts of this surface are successively presented to
it, the paper being rolled round a cylinder which is turned on its axis
by means of a clockwork movement. It is necessary to add that the
inscription is made, in the study of the walk of man, by means of two
styles, each corresponding to one of the feet.

The tracings thus obtained, which are read from left to right, are
sufficiently simple; but to understand them properly, it is necessary to
remember that the style undergoes a movement of ascensional displacement
during each pressure of a foot, and that, on the other hand, it
descends when the latter is separated from the ground. We also see, on
the tracing which it leaves, a line which ascends and then descends; the
meaning of this is that first the foot presses on the ground, and is
afterwards raised from it.

[Illustration: FIG. 116.--RUNNER FURNISHED WITH THE EXPLORATORY AND
REGISTERING APPARATUS OF THE VARIOUS PACES.]

On the tracing (Fig. 117), the line D relates to the right foot; the
line G, which is dotted so that it may not be confused with the
preceding, corresponds to the left foot. The line G first ascends; the
meaning of which is that the left foot presses on the ground; afterwards
it descends: this indicates that the pressure of the foot has ceased. It
is the same for the right foot. As we see, the pressures succeed each
other; when the left foot touches the ground, the right is separated
from it; when the latter presses the ground, it is the left which no
longer rests there.

The line O is related to the movements of the body, as indicated by the
oscillations of the head. We will neglect these.

But this tracing, which serves us for an example, is not, it must indeed
be said, of very easy reading; it would be still less so if the paces of
a horse were registered, for there would then be four lines, the
entanglement of which would cause greater complication.

These difficulties of reading need be no longer feared, if we transform
the tracing into a notation by means of the following diagram.

There are drawn (Fig. 118) below the graphic tracing two horizontal
lines (1, 2). From the point where the line D rises (commencement of the
pressure of the right foot), and from the point where this same line
descends (end of the same pressure), we let fall two vertical lines
joining the two horizontal ones mentioned above. At this plane, and
between the two vertical lines, we mark a broad white one (_a, b_). This
expresses, by its length, the duration of the period of pressure of the
right foot. In doing the same for the line G, we obtain for the
indication of a pressure of the left foot an interval of the same kind,
in which are marked cross-lines, or which is tinted gray, in order to
avoid all confusion with the preceding tracing.

[Illustration: FIG. 117.--TRACING OF THE RUNNING OF A MAN (AFTER
PROFESSOR MAREY.)

D, Pressures and elevations of the right foot; G, pressures and
elevations of the left foot.]

This notation can, with sufficient exactitude, be compared to that which
is employed in the musical scale. The horizontal lines 1 and 2 represent
the _compass_. We there also see _notes_; these are the bars indicating
the pressure, of which the value--that is to say, the duration--is
represented by the length of these bars. It is the same with regard to
the intervals of _silence_: these are expressed by the intervals which
separate the pressures, and correspond to the moments in which, during
certain paces, such as running, the body is raised from the ground.
Besides, we see intervals of this kind on the notation reproduced (Fig.
118) relative to the running of man.

[Illustration: FIG. 118.]

[Illustration: FIG. 119.]

In order to make the signification of these tracings still better
understood, we reproduce four varieties of them (Fig. 119).

The first notation is that of ordinary walking. The pressures succeed
each other regularly.

The second shows what takes place during the ascent of a staircase. At a
certain moment, the weight of the body is upon both feet at the same
time, one of them not quitting the lower step, until the other is
already in contact with the step above. Accordingly, there is thus
produced an overriding of the pressures.

The third is relative to running, and has already been represented in
Fig. 118. The pressures of the feet are separated by the times of
suspension.

The fourth also represents running, but in this case more rapid and
characterized by the shorter pressures, the slightly longer periods of
suspension intervals, and the quicker succession of movements.

Before putting aside the indications relating to the walking movements
of man--indications which it was necessary to give in order to render
intelligible those which are connected with the paces of the horse--we
have yet to fix the value of that which we call 'a step.'

It is generally admitted that a step is constituted by the series of
movements which are produced between the corresponding phases of the
action of one foot and that of the other--for example, between the
moment at which the right foot commences its pressure on the ground and
that at which the left foot commences its own. It is necessary to adopt
here another method of looking at it, and to regard the preceding as
being but a _half-step_. The step should then be defined as being
constituted by the series of movements which are executed between two
similar positions of the same foot--as, for example, between the
commencement of a pressure of the right foot and the similar phase of
the following pressure of the same foot. We shall soon understand the
importance of this definition.

Before entering on the details of the paces of the horse, it is
necessary to see how the limbs of the latter oscillate during the period
of a complete step; or, which is the same thing, to determine what the
displacements are which a limb executes between two similar positions of
its foot.

If we examine one of the limbs during a forward movement of the animal,
we see that this limb passes through two principal phases: (1) It is
raised from the ground; (2) it resumes contact with the ground. Each of
these phases is divided into three periods of time, which we proceed to
analyze in connection with the anterior limb.

[Illustration: FIG. 120.--SWING OF THE RAISED ANTERIOR LIMB (AFTER G.
COLIN).[71]

C, Lifting; B, suspension; A, placing.]

  [71] G. Colin, 'Traité de Physiologie Comparée des Animaux,' third
       edition, Paris, 1886.

The foot quits the ground (Fig. 120, C); this may be called _lifting_;
the limb is oblique in direction downwards and backwards. This same limb
is flexed and carried forward (Fig. 120, B), and, as it is supported by
the action of its flexors, this is the period named _suspension_; the
hoof is vertical. Then the limb is carried still further forward,
becoming extended (Fig. 120, A); the heel is lowered, and the foot,
being oblique, is directed towards the ground; this is the _placing_.

Then takes place pressure (Fig. 121). The foot has just been placed on
the ground; the limb is oblique in direction downwards and forwards;
this we call _commencement of the pressure_ (Fig. 121, A). Then the
body, being carried forward, whilst the hoof, D, is fixed on the ground,
the limb becomes vertical: this stage is _mid-pressure_ (Fig. 121, B).
Finally, the progression of the body continuing, the limb becomes
oblique downwards and backwards; it is now at the _termination of
pressure_ (Fig. 121, C), and proceeds to lift itself anew if another
step is to be made.

In conclusion, the inferior extremity of the limb describes, from its
elevation to its being placed on the ground, an arc of a circle around
its superior extremity (Fig. 121, D); whilst, during the pressure, it is
its superior extremity which describes one around its inferior
extremity, then fixed on the ground (Fig. 121, D).

[Illustration: FIG. 121.--SWING OF THE ANTERIOR LIMB ON THE POINT OF
PRESSURE (AFTER G. COLIN).

A, Commencement of the pressure; B, centre of the pressure; C,
termination of the pressure.]

If we simultaneously examine the two fore-limbs, we remark that when one
of them begins its pressure the other ends it, and _vice versâ_.

As to the hind-limbs, the oscillations are similar to those of the fore
ones. In the second half of the pressure--that is, when they are passing
from the vertical direction (Fig. 122, A) to extreme obliquity backwards
(Fig. 122, C)--the effect of their action is to give propulsion to the
body.

The fore and hind limbs make the same number of steps, and the steps
have the same length.

The limbs of any quadruped--but we make special allusion to those of
the horse--are divided into groups in the following manner:

The anterior pair constitutes the _anterior biped_. The _posterior
biped_ is that formed by the posterior limbs.

The name of _lateral biped_ serves to designate the whole formed by the
two limbs of the same side. The right fore-limb and the right hind-limb
form the _right lateral biped_. The two others form the _left lateral
biped_.

[Illustration: FIG. 122.--POSTERIOR LIMB, GIVING THE IMPULSE (AFTER G.
COLIN).

A, Commencement of pressure; B, centre of pressure; C, termination of
pressure.]

A fore-limb and hind-limb belonging to the opposite side form a
_diagonal biped_, which also takes the name of the fore-limb which forms
a part of it. Thus, _the right diagonal biped_ is formed by the
association of the right fore-limb and the left hind one. The _left
diagonal biped_ is, consequently, the inverse.

It is necessary to remember well these preliminary indications; it is
the only means of comprehending with facility that which is about to
follow.

Let us first return to the grouping of the limbs. The denominations
_anterior_ and _posterior bipeds_ render clearly perceptible the
comparison which consists in regarding a horse when walking as capable
of being represented by two men marching one behind the other, and
making the same number of steps. According as they move the legs of the
same side at the same time in 'covering the step,' or march in
contretemps step, we find reproduced all the rhythms which characterize
the different paces of the horse.

[Illustration: FIG. 123.--NOTATION OF THE AMBLING GAIT IN THE HORSE
(AFTER PROFESSOR MAREY).]

Professor Marey has studied these paces by a similar method to that
which he adopted for the walking of man, and which we have already
described. He employed hollow balls fixed under the hoofs, and a
registering apparatus with four styles, each corresponding to one of the
limbs. The tracing obtained is rather complicated, since two sets of
lines are found marked. But a notation similar to that of which we have
spoken can be discovered, and its exact signification should now be
determined. For this purpose, we have selected the most simple (see Fig.
123). We there see, placed in two superimposed lines, the pressure
markings of the right feet (white bands), and of the left feet (gray
bands). On the upper line are found those related to the fore-legs; the
lower lines contain those associated with the hind-legs. It is, in
brief, the superposition of two notations of the human walking
movements. And seeing that, as we have previously pointed out, we may
make a comparison between a quadruped and two men placed one behind the
other, it is easy to understand the significance of the superimposed
notations, if we accustom ourselves to look on them as the notations of
two bipeds.

To read these notations--that is, to learn to know what occurs at each
of the movements of the pace--it is necessary, indeed, to remember that
they should be examined in vertical sections; it is to each of these
sections--of these vertical divisions--that each of the movements which
we more particularly wish to analyze corresponds.

We proceed to study first the pace of ambling, because it is the most
simple; we shall then consider the trot, and, finally, we shall examine
that which is the most complicated, viz., the step.

[Illustration: FIG. 124.--THE AMBLE: RIGHT LATERAL PRESSURE.[72]]

  [72] The figures which, in the present study, reproduce the different
       paces, have been made from our articulated horse (see the note on
       p. 282).

=The Amble.=--To give an exact idea of the general character of the
amble, let us fancy the two men whom we discussed above marching one
behind the other and walking in step--that is, moving the legs of the
same side simultaneously. They will thus represent the amble, which,
indeed, results from the alternate displacements of the lateral bipeds;
the limbs of the same side (right or left) execute the same movements in
the same time.

This is what the notation indicates (Fig. 123). We there see that the
pressures of the right fore-foot, marked by the white bands in the upper
range, are exactly superposed on those of the right hind one, which are
marked by a similar band on the lower line; this means that the
pressures took place in the same time. We there see also a similar
arrangement of the gray bands, which has a similar significance for the
left fore and hind feet.

And if we recollect the three phases of pressure (see p. 289, and Figs.
121, 122), we shall comprehend, in looking at the diagrams, that, at the
initial stage (A), the limbs are commencing their pressure, and are
oblique downwards and forwards; that afterwards (B) the two limbs are
vertical, since they are at the middle of the pressure stage; and that
finally (C) they are oblique downwards and backwards, for it is then the
termination of their pressure (Fig. 124).

[Illustration: FIG. 125.--NOTATION OF THE GAIT OF THE TROT IN THE HORSE
(AFTER PROFESSOR MAREY).]

During the time that the right limbs are pressing (notation, white
bands) the left limbs are raised; afterwards these latter take up the
pressure (gray bands), and then the right limbs are raised in their
turn.

During the pace of ambling the weight of the body, which is wholly
sustained by the limbs of one side only, is not in equilibrium, so that
the limbs which are raised return by a brisk movement to the position of
support in order to re-establish it.

=The Trot.=--We have just seen that, in order to represent the amble,
the two marchers moved their right limbs simultaneously, and then their
left ones.

Let us suppose now that the hinder man anticipated by half a pace the
movement of the front one, then will be found realized the association
and the nature of the displacements of the limbs during the pace of the
trot.

By this anticipation of a half-step (we have defined, p. 288, what is to
be understood by the word _step_), it follows that when the marcher who
is in front advances his right leg it is the left leg of the marcher who
follows him that is carried in the same direction. We should thus
conclude from this that the trot is characterized by a succession of
displacements of the diagonal bipeds.

[Illustration: FIG. 126.--THE TROT; RIGHT DIAGONAL PRESSURE.]

[Illustration: FIG. 127.--THE TROT; TIME OF SUSPENSION.]

Indeed, if we examine the notation of this gait (Fig. 125), we see that
with the pressure of the right fore-foot is found associated the
pressure of the left hind-foot. It is, accordingly, a typical diagonal
biped (Fig. 126).

[Illustration: FIG. 128.--NOTATION OF THE PACE OF STEPPING IN THE HORSE
(AFTER PROFESSOR MAREY).

L, Right lateral pressure; D, right diagonal pressure; L´, left lateral
pressure; D´, left diagonal pressure.]

But it is necessary to add that these groups of pressures do not succeed
one another without interruption, except in the slow trot. In the
ordinary trot, or in that in which the animal's strides are very long,
the body between each of the double pressures which we have just been
considering is projected forward with such force that it remains for an
instant separated from the ground. This is what we designate by the name
of _time of suspension_ (Fig. 127). The notation in this case would be
slightly different from that which we reproduce above, in this sense:
that between the diagonal pressures there then would be found an
interval, since during the time the body is suspended none of the feet
can produce a pressure-mark (see, with regard to these intervals, the
notations of the running of a man, Fig. 118, and Fig. 119, 3, 4).

=The Walk.=--Although slow, a feature which would seem to make it
possible to permit its analysis in a horse when walking, this pace is
difficult to comprehend without sufficient preliminary study.

[Illustration: FIG. 129.--THE STEP: RIGHT LATERAL PRESSURE.]

[Illustration: FIG. 130.--THE STEP: RIGHT DIAGONAL PRESSURE.]

We saw above that in order to represent the amble the marchers had to
move the legs of the same side simultaneously. We have also just seen
that in order to represent the trot the marcher at the back had to
anticipate by a half-step. Suppose, now, that this same marcher
anticipates the man in front by a quarter-step only, or by a
half-pressure period, and thus will be found realized the order of
succession of the limbs in the gait or pace called the _walk_. The feet
meet the ground one after the other, since they are each in advance by
half the duration of a pressure. The strokes are four in number during
the period of a step of this pace; in the amble and in the trot they do
not exceed two, for then the limbs strike the ground in lateral diagonal
pairs.

[Illustration: FIG. 131.--THE GALLOP: FIRST PERIOD.]

[Illustration: FIG. 132.--THE GALLOP: SECOND PERIOD.]

[Illustration: FIG. 133.--THE GALLOP: THIRD PERIOD.]

[Illustration: FIG. 134.--THE GALLOP: TIME OF SUSPENSION.]

If we examine the notation of the pace of walking (Fig. 128), we see
that the right fore-foot commences its pressure when the right
hind-foot is in the middle of its own, and that the hinder left begins
in the middle of that of the right fore-foot, and that it is itself at
the midst of its pressure when the left fore-foot touches the ground,
etc. In a word, the foot-fallings occur in the following order and at
regular intervals--the fore right foot is here considered as acting
first: right fore, left hind, left fore, right hind, and so on in
succession.

[Illustration: FIG. 135.--NOTATION OF THE GALLOP DIVIDED INTO THREE
PERIODS OF TIME (AFTER PROFESSOR MAREY).

1, First period; 2, second period; 3, third period.]

As to the nature of the bipeds which succeed one another, it is easy to
understand them by means of the notation. In reading this from left to
right, we see that the associations of pressure are first made by the
two right feet, then by a right foot and a left one, then by two left
feet, and, finally, by a left and right. It is, accordingly, a
succession this time of lateral and diagonal pressures.

[Illustration: FIG. 136.--NOTATION OF THE GALLOP OF FOUR PERIODS IN THE
HORSE (AFTER PROFESSOR MAREY).

1, First period; 2, second period; 3, third period; 4, fourth period.]

Thus, we find at the start a right lateral pressure (Fig. 129), next a
right diagonal (Fig. 130), then a left lateral; finally, a left diagonal
pressure. It is thus that the initial letters L, D, L´, D´ further
indicate the notations represented in Fig. 128.

=The Gallop.=--The ordinary gallop is a pace of three phases. The first
is characterized by the fact that one hind-limb alone rests on the
ground (Fig. 131); in the second the animal is on a diagonal support
(Fig. 132); in the third it comes down on a fore-limb (Fig. 133). The
body is then raised (Fig. 134), and to this period of suspension succeed
anew the three modes of pressure indicated above.

The gallop is said to be from either right or left. In the gallop from
the right, the right fore-leg is the more frequently in advance of its
neighbour; it is the last to be placed on the ground. The left foot of
the posterior biped is the one which commences the action.

An entirely opposite arrangement characterizes the gallop from the left.

[Illustration: FIG. 137.--LEAP OF THE HARE (AFTER G. COLIN).]

The notation reproduced in Fig. 135 corresponds to the gallop from the
right. It is there seen, as we pointed out above, that in the first
phase the exclusive support of the left hind-foot takes place (1); that
afterwards, in the second, commence simultaneously, the pressures of the
left fore and the right hind foot (2); this is the left diagonal
support; and that finally, in the third, the body comes down on a
fore-limb, which is then the right (3); and that for a moment it is on
this limb alone that the animal rests.

To these three phases on the notation succeeds an interval; this is the
period of suspension.

The gallop of four phases only differs from the preceding in that the
foot-fallings of each diagonal biped occur at slight intervals, and give
distinct sounds. The notation is reproduced in Fig. 136.

[Illustration: FIG. 138.--THE LEAP.]

[Illustration: FIG. 139.--THE LEAP.]

[Illustration: FIG. 140.--THE LEAP.]

[Illustration: FIG. 141.--THE LEAP.]

=The Leap.=--The leap is an act by which the body is wholly raised from
the ground and projected upwards and forwards to a greater or less
distance.

It is prepared for by the flexing of the hind-limbs, which, by being
suddenly extended, project the body, and thus enable it to pass over an
obstacle.

This preparatory arrangement is very remarkable in the leap of the lion,
the cat, and the panther, which execute springs of great length; in the
horse, in which the leap is not an habitual mode of progression, this
flexion of the hinder limbs is less marked. With this animal the leap is
generally associated with the gallop; nevertheless, it is sometimes made
from a stationary position. In observing the hare or the rabbit, in
which the leap is habitual, we notice (Fig. 137) that the hind-limbs,
being extremely flexed, rest on the ground as far as the calcaneum, are
then straightened by the action of their extensors, become vertical and
then oblique backwards at the moment the body is thrown forward into
space by the sudden extension of these limbs.

The action of the extensors is energetic and instantaneous, and their
energy is greater than in ordinary progression, for it is required to
lift the body and to project it forcibly a more or less considerable
distance. It is the extreme rapidity of this action which enables the
animal to clear an obstacle, for without this condition the body would
be raised, but not separated from the ground.

First of all, in reaching the obstacle to be cleared, the horse prepares
to leap by taking the attitude of rearing; the hind-limbs are flexed and
carried under the body, the fore-quarters are raised, and the different
segments of the fore-limbs are flexed (Fig. 138).

[Illustration: FIG. 142.--THE LEAP.]

[Illustration: FIG. 143.--THE LEAP.]

One sudden trigger action produced by the violent contraction of the
extensors of the hind-legs then takes place, and the animal is projected
forwards, while he flexes the fore-legs more and more (Fig. 139). He
has then risen above the obstacle (Fig. 140). Then while he makes the
downward and forward balancing movement, and points his fore-limbs in
the same direction, he flexes the hind ones (Fig. 141). Whilst the
latter are further flexed, in order to pass the obstacle in their turn,
the fore-limbs which are extended come into contact with the ground
(Fig. 142). Finally, in the last phase of the leap, the animal, raising
himself in front, after the impact of his hind-feet has taken place
(Fig. 143), prepares to continue the pace at which he progressed before
meeting the obstacle which he had to clear.


THE END


_London: Baillière, Tindall and Cox, 8, Henrietta Street, Covent Garden,
W.C._




  THE
  ARTISTIC ANATOMY OF ANIMALS

[Illustration]




SECTIONAL INDEX


                                                                   PAGE

  =Generalities of Comparative Anatomy=                               1


  OSTEOLOGY AND ARTHROLOGY

  =The Trunk:=
    _Vertebral Column_                                                4
      Sacrum                                                         10
      Coccygeal vertebræ                                             11
      Direction and form of the vertebral column                     11
    _Thorax_                                                         12
      Sternum                                                        14
      Ribs and costal cartilages                                     14

  =The Anterior Limbs:=
    _Shoulder_                                                       20
      Scapula                                                        21
      Clavicle                                                       25
    _Arm_                                                            28
      Humerus                                                        28
    General view of the form of the forearm and hand                 34
      Forearm                                                        38
      Hand                                                           44

  =The Anterior Limbs in Certain Animals:=
    _Plantigrades_: Bear                                             49
    _Digitigrades_: Cat, dog                                         51
    _Unguligrades_: Pig                                              57
      Sheep, Ox                                                      60
      Horse                                                          64
    Proportions of the arm, the forearm, and metacarpus              70
    Articulations of the anterior limbs                              71
      Scapulo-humeral articulation                                   72
      Humero-ulnar articulation, or elbow                            74
      Radio-ulnar articulation                                       75
      Articulation of the wrist                                      75
      Metacarpo-phalangeal articulations                             76
      Interphalangeal articulations                                  77

  =The Posterior Limbs:=
    _Pelvis_                                                         78
      Iliac bone                                                     78
    _The Thigh_                                                      83
      Femur                                                          83
      Knee-cap                                                       85
    _The Leg_                                                        85
      Tibia                                                          86
      Fibula                                                         87
    _The Foot_                                                       87

  =The Posterior Limbs in Some Animals:=
    _Plantigrades_: Bear                                             90
    _Digitigrades_: Cat, dog                                         91
    _Unguligrades_: Pig                                              94
      Sheep, ox                                                      95
      Horse                                                          99
    Articulations of the posterior limbs                            105
      Coxo-femoral articulation                                     105
      Femoro-tibial articulation, or knee                           106
      Tibio-tarsal articulation, and of the bones of the tarsus     107

  =The Head in General, and in Some Animals in Particular:=
    Direction of the head                                           109
    The skull                                                       112
    The face                                                        118
    The skull of birds                                              127


  MYOLOGY

  =Muscles of the Trunk:=
    Pectoralis major                                                131
    Pectoralis minor                                                133
    Serratus magnus                                                 134

  =Muscles of the Abdomen:=
    External oblique                                                136
    Internal oblique                                                137
    Transversalis abdominis                                         138
    Rectus abdominis                                                138
    Pyramidalis abdominis                                           139

  =Muscles of the Back:=
    Trapezius                                                       140
    Latissimus dorsi                                                142
    Rhomboid                                                        144

  =The Cutaneous Muscle of the Trunk=                               147

  =The Coccygeal Region:=
    Ischio-coccygeal muscle                                         149
    Superior sacro-coccygeal muscle                                 150
    Lateral sacro-coccygeal muscle                                  150
    Inferior sacro-coccygeal muscle                                 150

  =Muscles of the Neck:=
    Mastoido-humeralis                                              150
    Sterno-mastoid                                                  153
    Omo-trachelian                                                  155
    Levator anguli scapulæ                                          156
    Splenius                                                        158

  =Infrahyoid Muscles:=
    Sterno-thyroid and sterno-hyoid                                 160
    Omo-hyoid                                                       160

  =Suprahyoid Muscles:=
    Mylo-hyoid                                                      161
    Digastric                                                       161

  =Panniculus of the Neck=                                          162

  =Muscles of the Anterior Limbs:=
    _Muscles of the Shoulder_                                       162
      Deltoid                                                       162
      Subscapularis                                                 163
      Supraspinatus                                                 164
      Infraspinatus                                                 165
      Teres minor                                                   166
      Teres major                                                   166
      Panniculus muscle of the shoulder                             167
    _Muscles of the Arm_                                            168
      Anterior region                                               169
        Biceps                                                      169
        Brachialis anticus                                          170
        Coraco-brachialis                                           170
      Posterior region                                              171
        Triceps                                                     171
      _Supplemental or Accessory Muscle of the Latissimus Dorsi_    173
    _Muscles of the Forearm_                                        174
      Anterior and external region                                  176
        Supinator longus                                            176
        First and second external radial                            176
        Supinator brevis                                            179
        Extensor communis digitorum                                 179
        Extensor minimi digiti                                      183
        Posterior ulnar                                             185
        Anconeus                                                    185
        Long abductor of the thumb                                  186
        Short extensor of the thumb                                 187
        Long extensor of the thumb                                  187
        Proper extensor of the index                                187
      Internal and posterior region                                 188
        Pronator teres                                              188
        Flexor carpi radialis                                       189
        Palmaris longus                                             189
        Anterior ulnar                                              191
        Superficial flexor of the digits                            193
        Long proper flexor of the thumb                             197
        Pronator quadratus                                          198
    _Muscles of the Hand_                                           199

  =Muscles of the Posterior Limbs:=
    _Muscles of the Pelvis_                                         200
      Gluteus medius                                                200
      Gluteus maximus                                               201
    _Muscles of the Thigh_                                          204
      Muscles of the posterior region                               205
        Biceps                                                      205
        Semi-tendinosus                                             206
        Semi-membranosus                                            207
      Muscles of the anterior region                                210
        Triceps                                                     210
        Tensor fascia lata                                          211
        Sartorius                                                   211
      Muscles of the internal region                                213
        Gracilis                                                    213
    _Muscles of the Leg_                                            213
      Muscles of the anterior region                                214
        Tibialis anticus                                            214
        Extensor proprius pollicis                                  219
        Extensor longus digitorum                                   219
        Peroneus tertius                                            224
      Muscles of the external region                                224
        Peroneus longus                                             224
        Peroneus brevis                                             225
      Muscles of the posterior region                               227
        Gastrocnemius                                               227
        Soleus                                                      228
        Plantaris                                                   228
        Popliteus                                                   228
        Superficial flexor of the toes                              229
        Flexor longus digitorum                                     230
        Tibialis posticus                                           230
        Flexor longus pollicis                                      231
    _Muscles of the Foot_                                           231
        Dorsalis pedis                                              231
    _Muscles of the Head_                                           232
      Masticatory muscles                                           232
      Masseter                                                      232
      Temporal muscle                                               234
      Cutaneous muscles of the head                                 234
        Occipito-frontalis                                          234
        Orbicularis palpebrarum                                     234
        Pyramidalis nasi                                            235
        Corrugator supercilii                                       235
        Zygomaticus major                                           235
        Zygomaticus minor                                           236
        Levator labii superioris proprius                           237
        Levator labii superioris alæque nasi                        238
        Transversus nasi                                            239
        Caninus                                                     239
        Orbicularis oris                                            240
        Triangularis oris                                           240
        Quadratus menti                                             240
        Prominence of the chin                                      240
        Buccinator                                                  241
          Maxillo-labialis                                          242
        Zygomatico-auricularis                                      242
        Temporo-auricularis externus                                243
        Scuto-auricularis externus                                  243
        Cervico-auricular muscles                                   243
        Cervico-auricularis superioris                              244
        Cervico-auricularis medius                                  244
        Cervico-auricularis inferioris                              244
        Parotido-auricularis                                        244
        Temporo-auricularis internus                                244
        Zygomatico-auricularis                                      245


  EPIDERMIC PRODUCTS OF THE TERMINAL EXTREMITIES OF THE FORE AND
  HIND LIMBS

  Claws                                                             247
  Plantar tubercles                                                 248
  Hoofs of the solipeds                                             250
  Hoofs of ox and pig                                               261

         *       *       *       *       *

  Proportions                                                       262
  Proportions of head of horse                                      273
    (front view)                                                    276

  Paces of the horse                                                282
    Amble                                                           293
    Trot                                                            294
    Walk                                                            296
    Gallop                                                          300
    Leap                                                            364




ERRATA


P. 105, _Articulations_ of the Posterior Limbs.

P. 107, Tibio-tarsal _Articulation_.




THE END


_London: Baillière, Tindall and Cox, 8, Henrietta Street, Covent Garden,
W.C._




  +--------------------------------------------------------------------+
  |                       TRANSCRIBER'S NOTES:                         |
  |                                                                    |
  | Footnotes have been moved to underneath the paragraph, table or    |
  | illustration they refer to.                                        |
  |                                                                    |
  | Illustrations have been moved so as to not disrupt the flow of the |
  | text. Page numbers in the List of Illustrations and in references  |
  | have not been changed, and are therefore not always correct.       |
  |                                                                    |
  | The Table of Contents and the Sectional Index are not complete and |
  | contain slightly different wording than the names of sections in   |
  | the text. This has been left as in the original work.              |
  |                                                                    |
  | The Errata have already been changed in the text.                  |
  |                                                                    |
  | The author uses the terms chromophotograph and chronophotograph    |
  | (and derivations of these words); these words have not been        |
  | changed. The correct term in these cases is chronophotograph.      |
  |                                                                    |
  | Page 143, Fig. 69: atlas is mentioned twice (nrs. 12 and 13); only |
  | nr. 13 indicates the atlas.                                        |
  |                                                                    |
  | The text used is that of the original work, including              |
  | inconsistencies in spelling, hyphenation and lay-out, and          |
  | differences between main text, footnotes and captions, except when |
  | mentioned below.                                                   |
  |                                                                    |
  | Changes made to the text:                                          |
  |   Some minor obvious typographical errors have been corrected      |
  |   silently.                                                        |
  |   Periods have been removed from some section headings for         |
  |   consistency.                                                     |
  |   Page 2, footnote [2]: Mathias-Duval changed to Mathias Duval     |
  |   (full name: Mathias-Marie Duval).                                |
  |   Page 23: _see_ replaced with see for consistency.                |
  |   Page 44 (footnote 12): Edward Cuyer changed to Édouard Cuyer as  |
  |   elsewhere.                                                       |
  |   Page 53, captions (2x): AA¹ changed to AA´ as in drawing and     |
  |   text.                                                            |
  |   Page 120, Fig. 63, caption: 14´, malar bone added, 14 changed to |
  |   anterior orifice of the cavity of the nasal fossæ (as in previous|
  |   figures).                                                        |
  |   Page 216: tendo-Achilles changed to tendo-Achillis as elsewhere. |
  |   Page 234: Fig. 0, 92 changed to Fig. 90, 2.                      |
  |   Page 254, Fig. 98: epternal changed to external.                 |
  |   Page 269, last paragraph: one anchor to same footnote deleted.   |
  |   Page 325: L, D, L', D' changed to L, D, L´, D´.                  |
  |   Footnotes 13, 17: La Natura changed to La Nature.                |
  +--------------------------------------------------------------------+





End of Project Gutenberg's Artistic Anatomy of Animals, by Édouard Cuyer