DIGESTIVE SYSTEM. 



195 



Fig. 143. Portion of the wall of 

 the small intestine, laid open to show 

 the valvulae conniventes (Brinton). 



the ileum Meckel's diverticulum may be present, rep- 

 resenting the last embryonic closure of the intestine. 

 The intestine has the same number of layers as the 

 stomach. The muscularis, however, consists of but 

 two strata, an inner circular and an outer longitudinal, 

 i. Mucosa. The mucosa is lined by simple co- 

 lumnar epithelium in 

 which many goblet 

 cells are present, par- 

 ticularly in the deeper 

 folds. Themembrana 

 propria and muscu- 

 laris mucosa are iden- 

 tical with those des- 

 cribed in the stomach. 

 The mucous surface of the small intestine is much 

 increased by means of folds, of which there are three 



mechanisms: 

 valvulcB conni- 

 ventes, villi, and 

 crypts of Lie- 

 berkuhn. 



(a) ValvulcB 

 Conniventes. 

 These are con- 

 centric, trans- 

 verse, crescen- 

 tic folds of the 

 mucosa, that 

 usually form 

 two-thirds of a 

 circle, although occasionally one forms an entire 

 circle or even a spiral. These valves are two or three 



Fig. 144. Mucous membrane of the jejunum, 

 highly magnified (schematic): i, i, Intestinal villi; 

 2, 2, closed or solitary follicles; 3, 3, orifices of 

 the follicles of Lieberkiihn (Testut). 



