254 FROGS, TOADS, AND NEWTS [CH. VIII 



much of it disappears, but the details of the process are 

 not known. The mucous membrane of about the first half 

 of the small intestine is thrown into two series of transverse 

 folds resembing the semilunar valves of the human heart; 

 they are so arranged as to prevent reflux of the food 

 towards the stomach while permitting it to move on 

 towards the large intestine. These folds are replaced 

 by irregular wrinklings in the portion of the duodenum 

 immediately adjoining the pylorus. In the last half of 

 the small, and throughout the large, intestine the mucous 

 membrane is thrown into longitudinal folds whose appear- 

 ance differs with the state of distension or contraction of 

 the organs concerned. By these folds and also by the villi 

 the area of the internal absorbing surface of the intestines 

 is largely increased. The length of the alimentary canal 

 is relatively small : this is in accordance with the animal 

 nature of the food : in the tadpole, which is chiefly, if not 

 entirely, herbivorous, the length of the canal is far greater 

 in proportion. 



Liver and Pancreas. The liver lies in the anterior part 

 of the abdomen, close behind the heart, and covers the 

 stomach ventrally. It is divided into several lobes, and 

 between the two main lobes, right and left, is situated the 

 gall-bladder, with which some of the ducts of the liver are 

 connected. The common bile-duct, by which the green- 

 coloured bile is conducted away, passes through the pancreas 

 which lies in the loop between the stomach and duodenum: 

 about halfway along the pancreas it receives the pancreatic 

 ducts, and eventually enters the duodenum very obliquely 

 with a slit-like aperture. Thus the bile and pancreatic 



