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THE
ARTISTIC ANATOMY OF ANIMALS
ARTISTIC
ANATOMY
OF ANIMALS
BY EDOUARD 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
BAILLIERE, 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 Ecole 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 ECOLE 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 ECOLE 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, Gericault. 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 Maitres.' Thirty
plates reproduced from the originals of Leonardo da Vinci,
Michelangelo, Raphael, Gericault, etc., with letterpress and a
history of plastic anatomy, Paris, 1890.
The manuscripts of Leonardo da Vinci of the Royal Library,
Windsor, 'Anatomy, Foliae A.,' published by Theodore Sabachnikoff,
with a French translation, written and annotated by Giovanni
Piumati, with an introduction by Mathias Duval. Edouard Rouveyre,
publisher, Paris, 1898.
Mathias Duval and Edouard 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 Ecole 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 ECOLE 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.
EDOUARD 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 VERTEBRAE 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 FELIDAE (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 deg. 110
57. SKULL OF THE HORSE: MEASURE OF THE FACIAL ANGLE BY THE
METHOD OF CAMPER. ANGLE BAC = 13 deg. 110
58. SKULL OF ONE OF THE FELIDAE (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, 'Precis 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 Edouard Cuyer: Paris, 1896.
'Artistic Anatomy of Man,' by J. C. L. Sparkes, second edition,
text with 50 plates: Bailliere, 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 _piliferes_ 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 vertebrae 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 vertebrae 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 vertebrae, whatever the length of
the neck of the animal. There are no more than seven vertebrae 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:
VERTEBRAE.
+------------+-----------+---------+---------+
| | 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 vertebrae
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 vertebrae are similarly
united to the iliac bones, between which they are fixed. The dorsal
vertebrae 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 vertebrae, the bones of that region,
which cannot be differentiated from the sacrum, having coalesced with
the bones of the pelvis.
VERTEBRAE.
+------------------+-----------+---------+
| | 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 vertebrae
and that of the dorsal is very variable; some serpents are devoid of
cervical vertebrae, having only dorsal ones--that is, vertebrae carrying
well-developed ribs.
VERTEBRAE.
+-------------------+-----------+---------+---------+
| | 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 vertebrae, 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
vertebrae when we examine in succession the bear, the cat, the dog, the
ox, and the horse. With regard to the other vertebrae 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 vertebrae 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 vertebrae, from their relation
to the trachea, are known as the _tracheal processes_.
The most marked characteristic of the dorsal vertebrae is furnished by
the spinous processes. They are long and narrow. As a rule, the spinous
processes of the foremost dorsal vertebrae are the most developed and
are directed obliquely upwards and backwards. As we approach the last
vertebrae 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 VERTEBRAE 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 vertebrae produce
the prominence at the anterior limit of the trunk, where the mane ends,
which is known as the _withers_.
The lumbar vertebrae 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 vertebrae
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
vertebrae 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 vertebrae 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 vertebrae 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 vertebrae, 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.
_Vertebrae 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 vertebrae, 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 vertebrae 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 Vertebrae.=--These vertebrae, 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 vertebrae--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
vertebrae. It is the _superior cervical ligament_, which arises from the
spinous process of the first cervical vertebrae, 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
vertebrae 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 vertebrae of the dorsal region.
The Thorax
The dorsal vertebrae 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 fossae. 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 vertebrae. 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 vertebrae, 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 vertebrae, 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
vertebrae; 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 vertebrae; 4, spinous processes of the
dorsal vertebrae; 5, coccygeal vertebrae; 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 role 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] Edouard Cuyer, 'Shape of the Region of the Wrist in Supination
and Pronation' (_Bulletin de la Societe 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
vertebrae; 9, sacrum; 10, coccygeal vertebrae; 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 vertebrae; 8, sacrum; 9,
coccygeal vertebrae; 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 fossae 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
vertebrae; 9, sacrum; 10, coccygeal vertebrae; 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
vertebrae; 9, sacrum; 10, coccygeal vertebrae; 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 fossae 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
vertebrae; 9, sacrum; 10, coccygeal vertebrae; 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.