The Alimentary Canal in Sauropsida

The alimentary canal of the Sauropsida is generally divided into an oesophagus, a simple stomach, a small intestine and large intestine, which last always terminates in a cloaca. It is invested by a peritoneal coat, which generally follows all the curvatures of the intestine. But in the Ophidia, the folds of the small intestine are united by fibrous tissue, and enclosed by a common sheath of peritonaeum.

The stomach is usually a simple dilatation of the alimentary canal, the cardiac and pyloric apertures of which are remote from one another; but, in the Crocodiles, and in most Birds, the pyloric and cardiac apertures are approximated. In many Crocodilia and Aves, there is a pyloric dilatation before the commencement of the duodenum.

In the Crocodilia, and in Aves, the walls of the stomach are very muscular, and the muscular fibres of each side radiate from a central tendon or aponeurosis. The thickening of the muscular tunic of the stomach attains its maximum in the graminivorous birds; and it is accompanied by the develops ment of the epithelium into a dense and hard coat, adapted for crushing the food of these animals. Birds commonly aid the triturating power of this gastric mill by swallowing stones; but this habit is not confined to them, crocodiles having been observed to do the same thing.

Birds are further remarkable for the development of a broad zone of glands in the lower part of the oesophagus, which is usually dilated, and forms a proventriculus, connected by a narrow neck with the above-mentioned muscular stomach or gizzard (gigerium).

Some Ophidia have a caecum at the junction of the small intestine with the large; and two such caeca, which sometimes attain a large size, are very generally developed in Aves. In this class also, the small intestine, not unfrequently, presents a caecal appendage, the remains of the vitelline duct. The duodenum of Birds constantly makes a loop, within which the pancreas lies, as in Mammalia.

The liver in the Sauropsida almost always possesses a gall-bladder, which is usually attached to the under surface of the right lobe, but in the Ophidia is removed to some distance from it.

A peculiar glandular sac, the Bursa Fabricii, opens into the anterior and dorsal region of the cloaca in birds.