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much more developed; and, by their increased dimensions, compensate for the more limited functions of the stomach.

69. In man this organ is simple, but divided into a cardiac and pyloric portion ;-thus occupying, as in a many other anatomical respects, a middle line between the carnivorous and herbivorous Mammalia. The inner surface of the stomach is covered with ruge, or wrinkles; formed by the mucous membrane, which lines the whole of the intestinal canal; and which forms valvular folds (called "valvulæ conniventes ") in the lower half of the duodenum, through the whole length of the jejunum, and upper part of the ileum; by which means the extent and surface of the whole canal are materially increased.

COLON AND CÆCUM.

70. The colon, which is the first of the large intestines, differs little in the Carnivora from the smaller ones,-the interior surface being smooth, and the capacity small and never cellulated: but in the Herbivora and in man its dimensions are much greater; and deep cells are formed in it, by ligamentous bands.

71. The cæcum, or caput cæcum coli, is the blind pouch or cul-de-sac, formed by a prolongation of the colon beyond the point at which the ileum enters its cavity. In the Carnivora, the cæcum is either altogether absent, or (when present) extremely small; while in herbivorous and frugivorous animals, it appears to per

form, in some measure, the functions of the stomach; and is generally developed in the inverse ratio of that organ;-being voluminous and complex where the stomach is simple, and proportionally small where the latter organ is complicated. In accordance with these remarks, we find no cæcum in the sloth, the stomach of which is complex; it is long, smooth, and ample, with a blunt apex, in ruminants; and generally large, sacculated, and distinctly glandular, in the Pachydermata. Those of the Rodentia which feed upon grain, (as the campagnoles, the hamsters, and the lemmings,) have the cæcum large; in those that are omnivorous (as the black rat) it is small; while in those which feed upon succulent vegetables (as the hare) it is exceedingly large;-having ten times the dimensions of the stomach.

72. In man the cæcum is tolerably large and globular, with a long "vermiform appendix", which may be regarded as the rudiment of an extended cæcum: it is found only in the human species, in the chimpanzee, the orang, the gibbons, (in the last very short,) and in the wombat. The cæcum is proportionately much larger in infants than in adults;—change of diet probably causing it to shrink in manhood. The colon is cellulated,—as in herbivorous animals.

73. In answer to the general statement, that the cæcum is larger in the Herbivora than in the Carnivora, Dr. Tyson states, that the hedgehog, which he considers frugivorous, has neither colon nor cæcum; but it is well ascertained, that this animal naturally feeds on serpents and insects. He also alleges, that the opossum, being

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carnivorous, has both a colon and a cæcum: to this, however, it may be replied, that the opossum lives chiefly on roots and wild fruits, though it also devours. poultry.

LIVER.

74. 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 of man); a right lateral lobe, with a lobular appendage (corresponding to the "lobulus Spigelii" and the "lobulus candatus"), and a small lobe or lobule on the left side. Through the whole animal series, however, the magnitude of the liver varies in the inverse ratio of the lungs.

75. 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 climates, 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-azotized articles taken along with the flesh of animals, by which means the system is supplied with more carbon than is needed. (See § 202.) So that the enlarged liver is attributable to gross living on a mixed diet, rather than to an exclusively animal diet.

76. There is another part of structure in which man differs from carnivorous animals, and resembles the Herbivora; namely, the immense number of perspiratory glands in the skin; by which the superfluous heat, generated by an excess of non-azotized food, escapes, -the retention of which in the system might be injurious. It is not improbable, that hydrophobia owes its origin to the inactivity of this function of the skin; -perspiration, in the dog, being given off principally by the tongue.

GENERAL REVIEW OF THE ORGANS.

77. The principal points of relation and difference, then, may be summed up in the following manner. In the absence of claws, and other offensive weapons; in the form of the incisor, cuspid, and molar teeth; in the arti culation of the lower jaw; in the form of the zygomatic arch; in the size of the temporal and masseter muscles, and salivary glands; in the length of the alimentary canal; in the size and internal structure of the colon and cœcum; in the size of the liver; and in the number of perspiratory glands: in all these respects, man closely resembles the herbivorous class of animals. The only points in which he appears to differ from them, and approach the Carnivora, are, in the enamel of the molar teeth being confined to the external surface, instead of being arranged in upright plates, alternating with plates

of ivory and of cortical substance: and in the stomach, which, though not so simple as that of the Carnivora, is much less complicated than that organ generally is in the Herbivora. Some of the latter, however, which are apparently formed for digesting grain and other concentrated food, have the stomach more simple, and the alimentary canal short; as the horse.

78. "The prevalent notion", says Dr. Combe, "that the digestive apparatus is simpler and shorter in carnivorous than in herbivorous animals,―merely because their food is more analagous in composition to their own bodies, and therefore requires less perfect digestion,seems to be unfounded; and to be negatived by the fact that, in the grain-eating birds,-in the constituent elements of whose food there is no such analogy,-the intestines, nevertheless, scarcely exceed in length those of the carnivorous birds ;- -a circumstance at variance with the notion of length being necessary solely on account of the great elaboration required for the conversion of vegetable into animal substance. The true principle-and it is important to notice it, as the error is generally adopted-appears to be, that where the food of the animal contains much nutriment in a small bulk, there the stomach and intestinal canal are simple and short; but where, on the contrary, it contains little nutriment in a large bulk, there great capacity, complexity, and length, become requisite to enable the animal to elaborate a sufficiency of nourishment for its subsistence, by taking in the requisite quantity from which it is to be derived."

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