ALIMENTARY CANAL

A cavity in the interior of an animal body in which the nutriment is taken to be digested, before it is conveyed by the nutritive ve els to the system: it affords the best organical characteristic of an animal, but presents various modifications of structure. Sometimes it is a simple cavity with one opening; sometimes a true canal, with an outlet or anus, distinct from the inlet or mouth; this canal may be divided into stomach and intestine, as in the oyster; or a mouth, pharynx, and oesophagus may precede the stomach; the cesop'hag us, again, may have one or two sacculi appended to it, called crops. The stomach may be subdivided into four bags, as in the ruminants, or into seven, as in the bottle-nose whale; and the intestines into small, blind, and large, forming, with their subdivisions, what are termed duodenum, jejunum, ileum, caecum, colon, and rectum. The caecum, again, may be single, or double as in most birds; or a single caecum may exist in addition to a double one, as in the hyrax, a small pachydermatous quadruped. Lastly, the various glandular organs which communicate with the alimentary canal are to be regarded as caecal proce es of that tube, since these are developed from it, and in this condition they are permanently retained by one or other of the lower animals: thus, in the sea-mouse, the liver is represented by long, branched, lateral proce es of the intestine; in the cod fish, . the pancreas is similarly represented by numerous caecal proce es of the duodenum. [s. 44]