TACEA, and some REPTILES.
In the NIAMMALIA, the intestinal canal is in general much shorter in the carnivorous than in the herbivorous animals, though to this there are a few exceptions. Thus, in the seal, which lives chiefly on fish, the intestines are very long, while in the sloth, which is entirely herbivo rous, they are extremely short. The length of the canal is greatest in the ruminantia and rodentia, being some times, in the former, in the proportion of 27 to 1 of the length of the body, and in the latter, in that of 12 or 16 to 1. It is said to be shortest in the noctule bat, (vcs pertilio noctula,) whose intestines are only twice the length of the body. Domestication seems to produce a remarkable change in this respect, as we are assured that in the wild boar, the intestines bear to the length of the body, a proportion of only 9 to 1, while in the do mestic animal of the same species, they are usually as 13 to 1. The same observation holds good in the cat and the bull, in both of which the intestines are longest in the domestic animals.
The distinction between large and small intestines in the mammalia is nearly universal, and, as in man, these parts of the intestinal canal are characterised by the greater number and length of the corrugations of the mucous membrane within the small intestines. Many of the mammalia, however, have no cercum, nor vermi form appendage ; and in those that have a c.ecum, this part appears rather a prolongation of the large intes tines than a distinct pouch, as in man. The ceecuin is smallest in the carnivorous quadrupeds. The folds of the mucous membrane in the small intestines are more faintly marked in most of the mammalia than in man, and in some species they appear to be altogether want ing. The valve of the colon, which is so remarkable in man, is, for the most part, also found in the mamma ; but in a few cases, especially in the hedge-hog, there is no such structure. The large intestines vary considerably in length and size, according to the food of the animal. In herbivorous quadrupeds they are
exceedingly long and large, and the colon is divided in to cells much more distinct than in man. This is par ticularly the case with the horse and the elephant ; in the former of which the colon is 24 feet long, while in a middle-sized dog its length does not exceed 6 or 8 hi dies. The division of the colon into cells is most re markable in the sheep.
In almost all the mammalia there are separate exter nal openings to the intestines and the urethra ; but in some cases, as the beaver and the sloth, these canals have a common termination ; and in the ornithorynchus this circumstance is so striking as to afford an addition al proof of the similarity between that animal and birds.
In the cetacea the intestines are usually very long, and the distinction into small and great intestines very com plete. The folds of the central membrane of the canal are remarkable in these animals, and in some cases the whole tube appears to be divided into very distinct cells, that act like valves, and prevent the return of the food from the sacral to the atlantal part of the canal.
The intestinal canal of BIRDS is proportionally much shorter than in mammalia, but it is longer in the grani vorous than in the carnivorous birds. The distinction into small and large intestines is very obscure, though in most birds there are two expansions of the canal, which we may call ceeca. In all birds the rectum termi nates in a particular expanded membranous cavity, cal led the cloaca, from the circumstance of its affording a common outlet to the excrements, and eggs. The form of the cloaca varies in the different species ; and that part of it through which the egg passes, and which had been called bursa Eabricii, is of an oval figure, and of a size oportioned to the eggs which are to pass through it. It is also largest in young birds. The villi in the small intestines are numerous and long, and have an ele gant appearance. They are most distinct in granivo rous birds.