210 PHYSIOLOGY AT THE FAKM. 



In the substance of the mucous lining of the intestines 

 numerous glands exist ; it is covered throughout with cylin- 

 drical epithelium that is to say, from the cardiac orifice of the 

 stomach to the fundament while the more common pavement, 

 that is, tesselated epithelium, covers the mucous membrane 

 from the mouth to the cardiac extremity of the gullet. The 

 cylindrical epithelium of the intestinal canal dips into the 

 various ducts which open upon the lining membrane. The 

 glands of the small intestines are of three principal kinds, named 

 respectively, after anatomists, the glands of Lieberkuhn, the 

 glands of Peyer, and the glands of Brunn or Brunner. 



The glands, or follicles, or crypts of Lieberkuhn are the 

 smallest of the whole. They are simple tubular recesses of 

 the intestinal mucous membrane, thickly distributed over the 

 whole surface of the large intestines, as well as of the small in- 

 testines. They cannot be seen in the small intestines without 

 the aid of a lens ; in the great intestines they are of greater 

 size, and the lower they are the larger, so that near the funda- 

 ment their orifices may be visible to the naked eye. Their 

 special use has not yet been discovered. 



The glands of Peyer are peculiar to the small intestines. 

 They are found in greater numbers the nearer to the ilio-csecal 

 valve or the junction of the small intestines with the great 

 intestines. Peyer's glands are either solitary or aggregated 

 in groups of several sizes, these groups being termed Peyer's 

 patches. The surface of the solitary glands are beset with 

 villi, which makes the chief difference between them and the 

 individual glands of the agminate patches. Each gland is a 

 closed sac from half a line to a line in diameter, either sunk 

 beneath or somewhat prominently raised on the surface of a 

 depression in the mucous membrane. The sac has no outlet. 

 The openings which surround it appear to be the openings of 

 follicles of Lieberkuhn. It seems probable that these shut 



