306 DIGESTION. 



instead of disappearing, as the rugae in the stomach would 

 under similar circumstances, they stand out at right angles 

 p. * to the general surface of the mucous 



membrane (fig. 72). Their functions 

 are probably these Besides (i), oifer- 

 ing a largely increased surface for 

 secretion and absorption, they proba- 

 bly (2), prevent the too rapid passage 

 of the very liquid products of gastric 

 digestion, immediately after their es- 

 cape from the stomach, and (3), by 

 their projection, and consequent inter- 

 ference with an uniform and untrou- 

 bled current of the intestinal contents, 

 probably assist in the more perfect 

 mingling of the latter with the secre- 

 tions poured out to act on them. 

 Glands of the Small Intestine. The glands are of three 

 principal kinds, named after their describers, the glands of 

 Fig m 73.1 Lieberkiihn, of Peyer, and of Brunn. The glands 

 or follicles of Lieberkiihn are simple tubular de- 

 pressions of the intestinal mucous membrane, 

 thickly distributed over the whole surface both 

 of the large and small intestines. In the small 

 intestine they are visible only with the aid of a 

 lens ; and their orifices appear as minute dots 

 scattered between the villi. They are larger in 

 the large intestine, and increase in size the nearer 

 they approach the anal end of the intestinal tube ; 

 and in the rectum their orifices may be visible to 

 the naked eye. In length they vary from ^ to 

 T V of a line. Each tubule (fig. 73) is constructed 



* Fig. 72. Piece of small intestine (previously distended and hardened 

 by alcohol) laid open to show the normal position of the valvulse con- 

 niventes. 



t Fig. 73. A gland of Lieberkiihn. 



