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Artistic Anatomy of Animals

Name: Artistic Anatomy of Animals
Author: Édouard Cuyer

by Édouard Cuyer

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Subjects

Zoological illustration Anatomy, Artistic Animals in art

In: Animal·Animals-Wild·Science - Biology

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Generalities of Comparative Anatomy

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

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

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

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

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

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

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

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

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

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

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

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

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

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

The following table shows their classification in some animals:

VERTEBRÆ.

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

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

VERTEBRÆ.

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

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

VERTEBRÆ.

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

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

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

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

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

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

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

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

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

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

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