370 



THE DIGESTIVE SYSTEM 



of absorption. Occasional leukocytes find their way into the epithelial 

 coat, whence they may penetrate the intercellular substance and enter 

 the intestinal canal. 



THE INTESTINAL GLANDS (Glands of Lieberkuhn; Mucous Crypts). 

 The intestinal glands occur throughout the entire extent of the small 

 and large intestines, including the appendix. They are simple tubules 



FIG. 345. SEVERAL VILLI FROM THE SMALL INTESTINE OF THE DOG, IN LONGITU- 

 DINAL SECTION. 



a, villi; 6, crypts of Lieberkuhn. Hematein and eosin. Photo. X 185. 



which extend the whole depth of the mucous membrane and in the 

 small intestine open upon the free surface between the bases of the 

 villi. Hence the lining epithelium of the glands becomes continuous 

 with that which clothes the villi. The glands are imbedded in the 

 diffuse lymphoid tissue of the corium; they rarely branch. They con- 

 sist of a lining epithelium and a basement membrane. 



The epithelium of the glands contains three types of cella: (1) 

 columnar cells; (2) goblet cells; and (3) the granule cells of Paneth. 

 The columnar and goblet cells resemble those which clothe the villi. 

 The columnar cells which line the neck of the glands, however, possess 



