564 THE INTESTINAL CANAL, BY E. KLEIN AND E. VERSON. 



tion are in some measure dependent upon the contraction of 

 the muscular coat. 



The villi of the small intestine, on the other hand, are eleva- 

 tions of the mucous membrane of more limited extent, which 

 make their first appearance in the descending portion of the 

 duodenum, where they are most closely arranged, and, becom- 

 ing more and more widely separated from one another, extend 



Fig. 107. 



Fig. 107. Section of a villus. From the intestine of a Rabbit. 

 a, epithelium ; b, stroma ; c, central cavity. 



to the free border of the iliocsecal valve. They vary consider- 

 ably in form. Sometimes they are cylindrical ; at others coni- 

 cal or clavate, or flattened and expanded like a leaf variations 

 that in part, at least, are occasioned by the degree of contrac- 

 tion of the general muscular tunic and of their own muscular 

 fibres, to which cause also their variation in length is attri- 

 butable. In man the length of the villi is from 0'4 to 0*6 

 of a millimeter, and the breadth from 0*06 to 0'12 of a millimeter. 

 In every villus one or two, or more rarely three, central 

 spaces are found, constituting the origin of the lacteals. (See 

 Chapter IX. on the Lymphatics.) 



