378 



THE DIGESTIVE SYSTEM 



zones. It therefore possesses no villi, and its simple somewhat longer 

 (about 0.5 millimeter) tubular glands extend from the free surface 

 almost to the muscularis mucosse. Villi are present, however, in the 

 embryo, but disappear about the sixth month (Johnson, 1913). 



The Lining Epithelium. The lining epithelium of the large in- 



01 and 



Tunica 

 muscularis 



Tunica 

 serosa 



FIG. 350. TRANSVERSE SECTION OF COLON OF DOG. 



The majority of the glands are cut longitudinally, some transversely, 

 a few obliquely. X45. 



testine is of the simple columnar variety and has only an indistinct cu- 

 ticular margin. That of the glands contains both columnar and goblet 

 cells, the latter being far more numerous than in the small intestine. 

 The large intestine contains no plicae circulares. 



The Lymphoid Tissue. The lymphoid tissue of the large intestine 

 occurs in the corium in diffuse form, and as solitary nodules, which 

 latter frequently break through the muscularis mucosffi and protrude 

 into the submucosa. Lymph nodules are especially abundant in the 



