Metazoa Ran a. 279 



tion it is to secrete mucin to keep the surface of the intestine 

 moist, and to dilute the intestinal digestive juice as it flows 

 from the follicles. 



At the junction of the . intestine and the stomach the 

 circular muscular coat is very much thicker, and forms a 

 sphincter valve (fig. 140). When it is contracted no food 

 can pass from the stomach into the intestine ; relaxation takes 

 place only when the food in the stomach has been sufficiently 

 acted on by the gastric juice. 



In the rectum both follicles and villi are absent, and 

 the mucous membrane consists simply of stratified squamous 

 cells with a few mucous glands. 



The liver is the largest organ in the body, and consists 



FIG. 142. GOBLET CELLS. (Quain.) 

 U. 



of a single right and a double left lobe. The two lobes are 

 united by a transverse commissure of liver substance. 

 The liver lobes are composed of an immense number of 

 polygonal lobules of small diameter (^ to ^ of an inch). 

 Each lobule is composed of many liver-cells, also polygonal 

 in form. The cells have extremely fine cell-walls, with 

 protoplasmic contents and nucleus, in which intracellular 

 and intranuclear networks can be readily made out. The 

 intercellular spaces open into minute ducts, lined by cubical 

 epithelium, which in turn communicate with the duct 

 already referred to as the bile-duct. The gall-bladder, 

 already mentioned, is practically an enlargement on the 

 course of the bile-duct, in which the surplus bile is stored. 



