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HANDBOOK OF PHYSIOLOGY. 



On then making a section it will be seen that, instead of disappearing, 

 they stand out at right angles to the general surface of the mucous 

 membrane (Fig. 192). Their functions are (1) that they offer a largely 

 increased surface for secretion and absorption, and (2) that they prevent 

 the too rapid passage of tho very liquid products of gastric digest-ion, 

 immediately after their escape from the stomach, and (3), by their pro- 

 jection, and consequent interference with an uniform and untroubled 

 current of the intestinal contents, that they assist in the more perfect 

 mingling of the latter with the secretions poured out to act on them. 



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

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



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

 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 ap- 

 pear as minute dots scattered between the villi. They are larger in the 





FIG. 192. 



FIG. 193. 



FIG. 194. 



FIG. 192. Piece of small intestine (previously distended and hardened by alcohol) laid open 

 to show the normal position of the valvulae conniventes. 



FIG. 193. Transverse section through four crypts of Lieberkuhn from the large intestine of the 



Smith.) 



FIG. 194. A rrland of Lieberkuhn hi longitudinal section. 



(Brinton.) 



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 vis- 

 ible to the naked eye. In length they vary from -^ to T V of a line. 

 Each tubule (Fig. 194) is constructed of the same essential parts as the 

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

 ment membrane, a layer of cylindrical epithelium lining it, and capil- 

 lary blood-vessals covering its exterior, the free surface of the columnar 



