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 mucosas. 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- 

 testine is of the 

 simple columnar 

 variety and has 

 only an indistinct 

 cuticular margin. 

 That of the glands 

 contains both col- 

 umnar and goblet 

 cells, the latter 

 being far more nu- 

 merous than in the 

 small intestine. 

 The large intestine 

 contains no plica? 

 circulares. 



The Lymphoid 

 Tissue. The lym- 

 phoid tissue of the 

 large intestine oc- 

 curs in the corium 

 in diffuse form, and 

 as solitary nodules, 

 w h i c h frequently 

 break through the 

 muscularis mucosas 

 and protrude into 

 the submucosa. The 

 f u n d u s of such 

 glands as may occa- 

 sionally be inclosed 



within' the lymph nodules are frequently prolonged into the superficial 

 portion of the submucosa, where they often possess alveolar dilatations. 

 Elsewhere the muscularis mucosa? forms a complete membrane which is 

 nowhere penetrated by the simple tubular intestinal glands. 



Lymph Nodules. Lymph nodules are especially abundant in the 



FIG. 350. SECTION OF LARGE INTESTINE OF DOG, SHOW- 

 ING INTESTINAL GLANDS (CRYPTS OF LIEBERKUHN) CUT 

 LONGITUDINALLY. 



Among the columnar cells lining the tubules are numer- 

 ous goblet cells. 



