The frog’s digestive canal.—The hinder end of the frog’s mouth opens (Fig. 163) into the gullet (gul.), a short wide tube which leads to a capacious bag called the stomach (st.). The termination of this is continuous with a coiled narrow tube called the small intestine (s. in.), which passes suddenly into a much wider large intestine or rectum. The rectum opens to the exterior, at the hinder end of the body, by an aperture (an.) known [Pg 232] as the anus. In addition to the digestive tube proper, two large digestive glands, the liver and the pancreas, should be carefully noticed. The liver (lr.) is a large, dark red organ, consisting of two lobes which lie at the sides of the stomach. It makes a digestive fluid called bile. The pancreas (pn.) is an elongated body which lies in the loop between the stomach and the first portion—called the duodenum (du.)—of the small intestine. It makes a digestive fluid called the pancreatic juice. In the frog both the bile and the pancreatic juice are discharged into the duodenum by one tube or duct (b.d.). Small digestive glands also occur in the inner wall of the stomach; these discharge a fluid called gastric juice into the cavity of the stomach. Fig. 163.—The Frog, dissected from the left side. gul, gullet; st, stomach; du, duodenum; s. int, small intestine; an. anus; lr, liver; pn, pancreas; b.d, bile duct; bl, urinary bladder; c.art, l.au, s.v, v, parts of the heart; cn. 3, “body” of 3rd vertebra; eus t. Eustachian tube; gl, glottis, leading to l.lng, left lung, and r.lng, right lung; n.a. 1, arch of 1st vertebra; p.na, internal opening of nostril; sp.cd, spinal cord; spl. spleen; tng, tongue; kd, kidney; ur, ureter; vo.t, vomerine teeth. The rabbit’s digestive canal—In its main features the digestive canal of the rabbit resembles that of the frog; here also the mouth opens into a long tube consisting of gullet, a bag-like stomach, a [Pg 233] small intestine, and a large intestine. There are also a liver and a pancreas which discharge their fluids—by separate ducts, however,—into the first part of the small intestine; and the stomach is supplied with gastric juice by small glands in its inner wall. There are, however, certain differences besides those of size in the digestive tubes of the two animals. In the first place, a fluid called saliva is poured into the rabbit’s mouth by the ducts of salivary glands which occur near the mouth. Secondly, the coils of the small intestine are very much more complicated than in the frog. And lastly, at the junction of small and large intestines there is given off, in the rabbit and in herbivorous mammals generally (when these have simple stomachs,—p. 261), a great, spirally-constricted tube which ends blindly in a finger-like process.