CLASS AMPHIBIA 



481 



end, but constricted at the posterior or pyloric end where it joins 

 the small intestine. The walls of the stomach are thick, con- 

 sisting of four layers : (1) the outer thin peritoneum; (2) a tough 

 muscular layer ; (3) a spongy layer, the submucosa ; and (4) an 

 inner folded mucous layer, the mucosa. The mucosa is made 

 up of glands lying in connective tissue. 

 Near the cardiac end the glands are 

 longer than at the pyloric end. 



The anterior portion of the small in- 

 testine is known as the duodenum; this 

 leads to the much-coiled ileum, which 

 widens into the large intestine. The ali- 

 mentary canal, as well as the urinary 

 bladder and reproductive ducts, open 

 into a sac-like cavity called the cloaca. 

 The inner layer of the intestine, the 

 mucosa, is much folded ; it consists of 

 ordinary absorptive cells and goblet 

 cells. 



The digest ive glands are the pancreas 

 and liver. The p ancre as lies between 

 the duodenum and the stomach. It is 



rostrale ; S, opening of 

 vocal sac ; T, tongue ; V, 

 vomer ; tp, tuberculum pre- 

 linguale. (From Holmes.) 



Fig. 411. — Mouth of 

 the frog widely opened. 

 E, Eustachian tubes; 

 G, glottis; /, lower jaw; 

 L, lateral subrostral fossa; 

 M, median subrostral 



a much-branched tubular gland which fossa; N, posterior nares; 



,, ,. ,. ,. n >i j 0, oesophagus; P, pulvinar 



secretes an alkaline digestive fluid and 

 empties it into the common bile-duct. 

 The liver is a large three-lobed reddish 

 gland which secretes an alkaline diges- 

 tive fluid called bile. This fluid is carried by bile capillaries 

 into the gall-bladder, where it is stored until food enters the in- 

 testine, when it passes into the duodenum through the common 

 bile-duct. 



Digestion begins in the stomach. The alkaline fluid secreted 



by the mucosa layer of the oesophagus and the acid gastric juice 



secreted by the glandular walls of the stomach digest out the 



proteid portion of the food by means of a. ferment, called pepsin, 



21 



