msnt. 



ALIMENTARY SYSTEM 365 



middle of the floor of the pharynx is a sHt-hke opening, the 

 glottis, which leads into the wind-pipe (Figs. 279 and 280). 



From the pharynx a tube known as the gullet or oesophagus 

 leads backwards in the body cavity to the stomach (Fig. 281), 

 which is spindle-shaped and separated by a sHght constriction, 

 the pylorus, from the intestine. The first part of the intestine, 

 known as the duodenum, is narrow and turns forward so as to lie 

 parallel with the stomach. It is succeeded 

 by another narrow tube, the ileum, 

 which runs backwards in several coils. 

 Duodenum and ileum are together 

 known as the small intestine : at its 

 hinder end this region opens suddenly 

 into a much wider tube, the rectum. 

 The length of the small intestine is from 

 4 to 5 inches ; that of the rectum is 

 about an inch and a quarter. The internal 

 surface of the intestine is increased by 

 folds of its lining. These are transverse in 

 the duodenum and longitudinal in the 

 ileum. The rectum passes without a 

 distinct anus into a cloaca, which receives 

 ventrally a thin walled, bilobed sac, the 

 urinary bladder, and dorsally the ducts 

 of the kidneys and in the female those 

 which bear the eggs. 



Besides numerous small glands in the mucous membrane, 

 the alimentary canal receives the secretions of two large glands, 

 the Kver and the pancreas. The liver is a large, reddish-brown 

 structure in the forepart of the belly. It consists of a right and a 

 left lobe and a small median lobe which unites them. The left 

 lobe is the larger and is itself deeply cleft into two. Between the 

 right and left lobes lies the gall-bladder, which receives the green 

 bile secreted by the liver and passes it by the bile-duct into the 

 duodenum. The pancreas is an oblong, creamj^-white structure 

 lying between the stomach and duodenum. It is traversed by 

 the bile-duct, into which it passes the pancreatic juice which 

 it secretes. 



— A diagram of a 

 transverse section through 

 the ileum of the frog. 



cm., Circular muscle layer ; c.t., 

 connective tissue ; ep., epithelium 

 which lines the gut ; l.m., longi- 

 tudinal muscle layer ; msnt. , 

 mesentery ; per., peritoneum 

 rid., longitudinal ridges of ileum. 



