CHAP. XIV.] 



ALIMENTATION. 



161 



sna ggy or velvety appearance to the membrane. These projec- 

 tions or villi, as they are termed, extend throughout the whole 

 length of the small intestine, and are especially provided for 

 purposes of absorption. Each villus is a portion of the mucous 

 membrane, and consists of an external layer of columnar cells 

 attached to a basement membrane, and a central mass of lym- 

 phoid tissue. In the centre of each villus is the rootlet of a 

 lacteal vessel, while under the basement membrane is a network 

 of capillaries. The blood-vessels and lymphatics of the villi 

 communicate with networks of both vessels in the sub-mucous 

 coat below. Besides these projections formed for absorption, 



FIG. 99. SECTION THROUGH THE LYMPHOID TISSUE OF A SOLITARY GLAND. 

 (Cadiat.) a, centre of the gland, with the lymphoid tissue fallen away; 6, epithe- 

 lium of mucous membrane ; c, c, villi, with epithelium partly broken away ; d, crypts, 

 or glands, of Lieberkiihn. 



the mucous membrane is thickly studded with secretory glands ; 

 the larger number of these, found all over the surface of the 

 intestine, are called the glands or crypts of Lieberkiihn, while a 

 smaller number, found chiefly in the duodenum, are named the 

 duodenal or Brunner's glands. These glands are supposed to 

 secrete the intestinal juice, succus entericus. 



Again, in the corium of the mucous coat the lymphoid tissue 

 is collected into numerous solitary glands or follicles, and into 

 groups of glands, the Peyer's patches, the functions of which 

 are not yet clearly understood. 



