The pyloric valve is, as a rule, well marked. In some species there is a small supplementary cavity, which immediately precedes it, and receives the orifice of the gizzard.
The intestine has a length about rnidway between that of the Reptilian and Mammalian bowel. But although longer than in either of the preceding classes, it retains considerable simplicity of form. It presents, however, much variety, both in its length and in the number and appearance of its convolutions ;— differences which, as usual, are related (though not very closely) to the food and habits of the animal. The duodenum which immediately follows the pylorus has the form of a long loop or fold, the concavity of which includes the pancreas. The small intestine, more or less folded, terminates in a large intestine, the commencement of which receives two cmcal tubes, one on each side. These exca offer remarkable differences in length :—varying from papilliform offsets, as in the Solan-goose, to processes three feet long, as in the Grouse. Sometimes only one is present. The short and straight large intestine is continued from the termination of the small intestine, without any distinct valve, to end in a cloaca com mon to the digestive, urinary, and generative organs. Connected with the small intestine is an appendage, supposed to be a relic of the duct of communication between the yolk bag and intestine of the chick. It is de void of a muscular tunic, and in some birds equals or exceeds the size of the cmca them selves..
Mammalia.—The form, length, and arrange ment of the alimentary canal vary so much in the different orders of INIammalia, that it will be necessary briefly to state its pecu liarities in each.
In the Carnivora the shape of the stomach approaches that of the human organ : it has a cardiac pouch, and a greater and lesser curvature. The intestine is short, its length being to that of the body as* 5 to 1 in cats and dogs, and 8 or 9 to 1 in the hyxna and bear, but reaching 15 to 1 in the Phoca vitatina, one of the amphibious seals. The mucous membrane is destitute of folds. The convolutions of the small intestine are few and simple. The caecum is short, and
scarcely wider than the rest of the large intestine.1- And the latter segment of the canal is short, wide, and cylindrical.
The Insectivora have a very similar intestinal tube. The simple and elongated stomach is transverse to the axis of the body. In some genera, its spherical cardiac pouch is enlarged, while its lesser curvature becomes shortened. The intestine is short—from three to six times the length of the body ; it has no cmcum, and a nearly uniform diaineter. Its mucous membrane exhibits zig-zag folds, which run longitudinally throughout its whole length. • In the Cheiroptera three chief varieties of stomach have been distinguished by envier. The first approaches that seen in the preceding order, and belorws to those members of this group which feed upon insects. Here the nearly spherical organ has a cardia and pylorus, which are situated close to each other. The second form is seen in those which subsist by sucking the blood of animals : it differs from the preceding in being longer, and more conical from cardia to pylorus. The third, which obtains in the frugivorous division, is very different from both the pre Th7cs, in the Pteropus the stoinach is a low" tube, placed transversely to the axis of thebody. One-third of its length is formed by the cardiac pouch, which lies to the left of the cesophageal aperture, and is divided into two by a slight constriction, while its terminal or pyloric third is bent back so as to be parallel and near to the middle portion. The mucous membrane of this stomach is folded longitudinally ; the left subdivision of the cardia is smooth, and the lower part of the cesophams — which is somewhat dilated — differs from the upper.
The pylorus is well marked in all the Cheiroptera, and the intestine, which is much narrower than the stomach, and is devoid of cmcum, is of nearly uniform diameter. It often presents concentric windings or coils. Its length varies greatly ;—thus, in the frugi vorous Pteropus it is six or seven times, in the insectivorous Bat only twice, the length of the body.