The Stomach.—The position and form of the stomach are also of significance. In the carnivora, it is only a small roundish sack, exceedingly simple in structure; while in the vegetable feeders it is oblong, lies transversely across the abdomen, and is more or less complicated with ringlike convolutions—according to the nature of the food. This appears conspicuously in the primates, which include man, in the Rodentia, Edentata, Marsupials, and, above all, in the Ruminants. In the latter, it presents a series of from four to seven wide, adjoining and communicating sacks.
At a first superficial glance at the exteriors of the stomachs of the carnivora and that of man, we apparently perceive a far closer resemblance than between man’s stomach and that of a herbivorous animal. In one sense, there can be no question that there is a closer similarity; in another sense, it is not so. In man this organ is simple, but is divided into a cardiac and pyloric portion—thus occupying, as in many other anatomical respects, a middle line between the carnivorous and herbivorous mammalia. The inner surface of the stomach is covered with rugæ, or wrinkles, formed by the mucous membrane, which lines the whole intestinal canal, and which forms valvular folds; while in the carnivora the stomach is a simple globular sac, without these corrugations. As Dr Trall observed[7]:
“Some may imagine, at a first glance, a closer resemblance between the human stomach and the lion’s than between the human and that of the sheep. But when they are viewed in relation to their proper food, their closer resemblance will vanish at once. It should be particularly observed that, so far as mere bulk is concerned, there is a greater similarity between the food of frugivorous animals and carnivorous animals than between frugivorous and herbivorous. The digestion and assimilation of coarse herbage, as grass, leaves, etc., requires a more complicated digestive apparatus than grains, roots, etc., and these more so than flesh and blood. The structure of the stomach, therefore, in such cases, seems precisely adapted to the food we assume Nature intended for it.”[8]
The Liver.—Dr John Smith, in calling attention to the many distinctions between the bodily structure of man and that of the carnivora, pointed out the following differences among others:—
“In the carnivora and rodentia, which present the most complex form of liver among the mammalia, there are five distinct parts; a central or principal lobe, corresponding with the principal part of the liver in man; a right lateral lobe, with a lobular appendage, corresponding to the ‘lobulus Spigelii’ and the ‘lobus caudatus,’ and a small lobe or lobule on the left side. Through the whole animal series, however, the magnitude of the liver varies in inverse ratio to the lungs.
“In man, the liver is much less developed than the same organ in many other mammalia; and presents, as rudimentary indications, certain organs which are in other animals fully developed. Europeans, and the inhabitants of Northern climes, who partake more of animal food, have the liver much larger, and its secretions more copious, than the inhabitants of warm climates. Perhaps this, in some measure, depends upon the amount of non-azotised articles taken along with the flesh of animals, by which means the system is supplied with more carbon than is needed. So that the enlarged liver is attributable to gross living on mixed diet, rather than to an exclusively animal diet.”
This author also says elsewhere (p. 79):
“The temporal and masseter muscles, by which the motion of the lower jaw is effected, are of immense size in carnivorous animals. The temporal muscle occupies the whole side of the scull, and fills the space beneath the zygomatic arch, the span and spring of which are generally an index of the volume of this muscle; while the extent and strength of the arch indicate the development of the masseter muscle. On the contrary, the pterygoid muscles, which aid the lateral movement of the jaw, are extremely small. The zygoma is of great size and strength in the carnivora; consisting of a long process of the masseter bone, overlaid by the usual process of the temporal bone, which is equally strong. The arch extends not only backward but upward, by the bending down of the extremity; the line of anterior declination falling precisely on the centre of the carnassière tooth—the point in which the force of the jaws is concentrated, and where it is most required for cutting, tearing, and crushing their food. In ruminants, the zygomatic arch is short, and the temporal muscles are small; but the masseter muscle on each side extends beyond the arch, and is attached to the greater part of the side of the maxillary bone. The pterygoid fossa is ample, and its muscles are largely developed. The arch is small in man, the temporal muscles moderate, and the force of the jaws comparatively weak.”
The Placenta.—Let us now turn to another important distinction between the carnivorous and non-carnivorous animals. Of these, perhaps the most important is the character of the placenta—one of the most distinguishing marks or characteristics of any species of animal. This subject has been so well and ably summed up by Professor Schlickeysen, in his “Fruit and Bread” (pp. 48-57), that I cannot do better than quote the main portion of the argument, as stated by this learned and able author. He says:
“We now come to consider the peculiar structure, form and size of the placenta, as well as the exact method by which, through it, in different species of animals, the nourishment is effected. One of the most striking differences presented in placental animals relates to the method of union between the mother and the fœtus. There are two very distinct types of the placenta, and, according to Professor Huxley, no transitional forms between them are known to exist. These types are designated as follows:—