260 HAND-BOOK OF PHYSIOLOGY. 



tine, and at forty to seventy in the same area at the lower part. They 

 vary in form even in the same animal, and differ according as the lym- 

 phatic vessels they contain are empty or full of chyle; being usually, in 

 the former case, flat and pointed at their summits, in the latter cylindri- 

 cal or cleavate. 



Each villus consists of a small projection of mucous membrane, and 

 its interior is therefore supported throughout by fine adenoid tissue, which 

 forms the framework or stroma in which the other constituents are con- 

 tained. 



The surface of the villus is clothed by columnar epithelium, which 

 rests on a fine basement membrane; while within this are- found, reckon- 

 ing from without inward, blood-vessels, fibres of the muscularis mucosce, 

 and a single lymphatic or lacteal vessel rarely looped or branched (Fig. 

 192); besides granular matter, fat-globules, etc. 



^ 





' > 



FIG. 190. FIG. 191. 



FIG. 190. Section of small intestine showing villi, Lieberkiihn's glands and a Peyer's solitary 

 gland, m, m, muscularis mucosee. (Klein and Noble Smith.) 



FIG. 191. Vertical section of a villus of the small intestine of a cat. a, striated basilar border of 

 the epithelium ; b, columnar epithelium ; c, goblet cells ; d, central lymph-vessel ; e, smooth muscular 

 fibres; /, adenoid stroma of the villus in which lymph. corpuscles lie. (Klein.) 



The epithelium- is of the columnar kind, and continuous with that 

 lining the other parts of the mucous membrane. The cells are arranged 

 with their long axis radiating from the surface of the villus (Fig. 191), 

 and their smaller ends resting on the basement membrane. The free 

 surface of the epithelial cells of the villi, like that of the cells which cover 

 the general surface of the mucous membrane, is covered by a fine border 

 which exhibits very delicate striations, whence it derives its name, "stria- 

 ted basilar border." 



Beneath the basement or limiting membrane there is a rich supply of 

 blood-vessels. Two or more minute arteries are distributed within each 

 villus; and from their capillaries, which form a dense network, proceed 

 one or two small veins, which pass out at the base of the villus. 



The layer of the muscularis mucosce in the villus forms a kind of thin 

 hollow cone immediately around the central lacteal, and is, therefore, 



