306 DIGESTION. 



As in structure, so probably in function, they resemble the 

 pancreas ; or at least stand to it in a similar relation to 

 that which the small labial and buccal glands occupy in 

 relation to the larger salivary glands, the parotid and 

 submaxillary. 



The Villi (figs. 8 1, 82) are confined exclusively to the 

 mucous membrane of the small intestine. They are minute 

 vascular processes, from a quarter of a line to a line and 

 two-thirds in length, covering the surface of the mucous 

 membrane, and giving it a peculiar velvety, fleecy appear- 

 ance. Krauss estimates them at fifty to ninety in number 

 in a square line, at the upper part of the small intestine, 

 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 lymphatic vessels they contain are empty 

 or full of chyle; being usually, in the former, case, flat 

 and pointed at their summits, in the latter cylindrical or 

 clavate. 



Each villus consists of a small projection of mucous- 

 membrane, and its interior is therefore supported through- 

 out by fine retiform or adenoid tissue, which forms the- 

 framework or stroma in which the other constituents are 

 contained. 



The surface of the villus is clothed by columnar epithe- 

 lium, which rests on a fine basement membrane ; while 

 within this are found, reckoning from without inwards,, 

 blood-vessels, fibres of the muscularis mucosce, and a single 

 lymphatic, or lacteal vessel rarely looped or branched (fig. 

 8l) ; besides granular matter, fat-globules, etc. 



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. 81), and their smaller ends 

 resting on the basement membrane. Some doubt exists 

 concerning the minute structure of these cells and their 

 relation to the deeper parts of the villus. 



