PHYSIOLOGICAL ANATOMY OF THE SMALL INTESTINE. 



261 



constituent of the intestinal juice. The length of the tubules is equal to the thickness ot 

 the mucous membrane and is about 7 * 7 of an inch. Their diameter is about ^^ of an 

 inch. In man, they are cylindrical, terminating in a single, rounded, blind extremity, 

 which is frequently a little larger than the rest of the tube. These tubules are the chief 

 agents concerned in the production of the fluid known as the intestinal juice. 



FIG. 65. Intestinal tubules; magnified 100 diameters. (Sappey.) 



A. From the dog. 1, excretory canal ; 2, 2, primary branches ; 3. 8, secondary branches; 4, 4, terminal culs-de-sac. 



B. From the ox. 1, excretory canal ; 2, principal branch, dividing into two ; 8, branch undivided ; 4, 4, terminal 



culs-de-sac, 



C. From the sheep. 1, trunk; 2, 2, branches. 



D. Single tube, from the pi?. 



E. From the rabbit and hare. 1, simple gland ; 2, 8, 4, bifid glands ; 5, compound gland from the duodenum. 



The intestinal villi, though chiefly concerned in absorption, are most conveniently 

 considered in this connection. These exist throughout the whole of the small intestine 

 but are not found beyond the ileo-cascal valve, although they cover that portion of the 

 valve which looks toward the ileum. Their number is very great, and they give to the 

 membrane its peculiar and characteristic velvety appearance. They are found on the 

 valvulse conniventes as well as on the attached portions of the mucous membrane. In 

 the duodenum and jejunum, they are most numerous. In these parts, there are from 

 7,200 to 13,000 villi to a square inch, and, in the ileum, from 5,YOO to 10,000 to a square 

 inch. Sappey estimates, on an average, about V,200 to the square inch and more than ten 

 millions (10,125,000) throughout the whole of the small intestine. The villi vary some- 

 what in form in different animals. In the human subject, they are flattened cylinders 

 or cones. In the duodenum, where they resemble somewhat the elevations found in the 

 pyloric portion of the stomach, they are shorter and broader than in other situations 

 and are more like flattened, conical folds. In the jejunum and ileum, they are in the 

 form of long, flattened cones and cylinders. As a rule, the cylindrical form predominates 

 in the lower portion of the intestine. In the jejunum they attain their greatest length, 



