FOOD AND DIGESTION. 373 



disappearing, they stand out at right angles to the general surface of 

 the mucous membrane (fig. 256). Their functions are (1) to afford a 

 largely increased surface for secretion and absorption, and (2) to prevent 

 the too rapid passage of the very liquid products of gastric digestion, 

 immediately after their escape from the stomach, and (3) to assist in 

 the more perfect mingling of the latter with the secretions poured out 

 to act on them, by their projection, and consequent interference with 

 an uniform and untroubled current of the intestinal contents. 



Glands. The glands are of three principal kinds: viz., those of (1) 

 Lieberkiihn, (2) Brunner, and (3) Peyer. 



(1.) The glands or crypts of Lieberkiihn are simple tubular depres- 



P ig. 259. Transverse section of injected Peyer's glands (from K811iker). The drawing was 

 taken from a preparation made by Frey: it represents the fine capillary- looped network spreading 

 rrom the surrounding blood-vessels into the interior of three of Peyer's capsules from the intestine 

 of the rabbit. 



sions of the intestinal mucous membrane, thickly distributed over the 

 whole surface both of the large and small intestines. In the small in- 

 testine 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 ^ of an 

 inch. Each tubule (fig. 258) is constructed of the same essential part as 

 the intestinal mucous membrane, viz., of a fine membrana propria, or 

 basement membrane, a layer of columnar epithelium lining it, many of 

 which are goblet cells, and capillary blood-vessels covering its exterior, 

 the free surface of the columnar cells presenting a striated appearance. 



