58 GENERAL ANATOMICAL CHARACTERS 



dilatation of the alimentary canal, as in Figs. 20, 21, but in others 

 it undergoes remarkable modifications and complexities. The lining 

 of the stomach is thickly beset with tubular glands, which are 

 generally considered to belong to two different forms, recognisable 

 by their structure, and different in their function the most 

 numerous and important secreting the gastric juice (the active 

 agent in stomachic digestion), and hence called " peptic " glands, 

 while the others are concerned only in the elaboration of mucus. 

 The relative distribution of these glands in different regions of the 

 walls of the stomach varies greatly in different animals, and in 

 many species there are large tracts of the mucous membrane which 

 do not secrete a fluid having the properties of gastric juice, but 

 often constitute more or less distinct cavities devoted to storing 



U 



FIG. 20. Stomach and pancreas of the Genet. Posterior or dorsal surface, ce, (Esophagus ; 

 s, pancreas ; pd, pancreatic duct ; bd, biliary duct from the liver. (From Mivart, Proc. Zool. 

 Soc. 1882, p. 305.) 



and perhaps S9ftening or otherwise preparing the food for digestion. 

 Sometimes there is a great aggregation of glands forming distinct 

 thickened patches of the stomach wall, as in the Beaver and Koala, 

 or even collected in pyriform pouches with a common narrow 

 opening into the cavity, as in the Manatee and the curious African 

 Eodent Lophwmys. The action of the gastric fluid is mainly 

 exerted upon the nitrogenous elements of the food, which it 

 dissolves and modifies so as to render them capable of undergoing 

 absorption, effected partly by the blood-vessels of the stomach, 

 although the greater part passes through the pylorus, an aperture 

 surrounded by a circular muscular valve, into the intestinal canal. 

 Here it comes in contact with the secretion of a vast number of 

 small glands called the crypts of Lieberkuhn, somewhat similar 

 to those of the stomach ; and also of several special glands of a 

 different character, namely, the small racemose, duodenal, or 



