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 
py 
Fia. 20.—Stomach and pancreas of the Genet. Posterior or dorsal surface. w, Esophagus ; 
8, pancreas ; pd, pancreatic duct; bd, biliary duct from the liver. (From Mivart, Proc. Zool. 
Soc. 1882, p. 305.) 
and perhaps softening or otherwise preparing the food for digestion. 
Sometimes there is a great ageregation of glands forming distinet 
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 
Rodent Lophiomys. 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 
