HIGH SCHOOL ZOOLOGY. 41 



lined by a continuation of the lining epithelium of the stomach, 

 which dip down into the submucous coat, and consequently 

 make the gastric mucous membrane of considerable thickness. 

 The stomach forms a blind projection beyond the pyloric aper- 

 ture ; it is therefoi'e said to be of the ccecal type, whereas in 

 many other fishes its long axis is directly continued into the 

 intestine. After the food has been subjected to the action of 

 the gastric juice, which rendere some of its ingredients more 

 capable of being absorbed, it passes through the pyloric valve 

 (which is simply a local thickening of the circular muscular 

 layer) into the small intestine. Here it is at once mingled with 

 the secretion of two important glands, the liver and pancreas 

 to be afterwards described; further altered thereby, and finally 

 for the most pai't absorbed by the walls of the tube and partly 

 ])ropelled further into the large intestine. 



52. In most higher animals there are folds or projections of 

 the mucous membrane which facilitate this absoi-ption by the 

 small intesfeine ; except for longitudinal folds, the mucous mem- 

 brane in the catfish is smooth, and the amount of epithelial sui-- 

 face is increased by tubes projecting into the submucous tissue 

 which are however shorter and %vider than the gasti-ic tubes. 

 The chief difierence in the structure of the large intestine is in 

 its greater size, and more developed musculature. 



53. Of the glandular appendages of the small intestine, the 

 liver is the most important. It is formed for the most part of 

 hepatic cells which are continuous with the lining epithelial 

 cells of the intestine through the bUe-duct. The cells are sus- 

 pended in a delicate frame- work of connective tissue, peneti-ated 

 by blood-vessels, and the liver is therefore very soft in its texture. 

 It has two lobes, a right and a left, each divided into subsidiary 

 lobes, and on the xmder surface of the right of these is the gall- 

 bladder, a reservoir communicating by several ducts with the 

 liver, but only by one with the intestine. Side by side with the 



4 



