454 



THE HUMAN BODY 



off-shoot of the lymphatic system; sometimes in the form of a 

 single vessel with a closed dilated end, and sometimes as a net- 

 work formed by two main vessels with cross-branches. During 

 digestion these lymphatics are filled with a milky-white liquid ab- 

 sorbed from the intestines, and they are accordingly called the 

 lacteals. They communicate with larger branches in the sub- 

 mucous coat, which end in trunks that pass out through the mes- 

 entery to join the main lymphatic system. Finally, in each villus, 



FIG. 131. Villi of the small intestine; magnified about 80 diameters. In the 

 right-hand figure the lacteals, a, &, c, are filled with white injection; d, blood- 

 vessels. In the left-hand figure the lacteals alone are represented, filled with a 

 dark injection. The epithelium covering the villi, and their muscular fibers, are 

 omitted. 



outside the lacteals and beneath the muscular layer of the villus, 

 is a close network of blood-vessels. 



Opening on the surface of the small intestine, between the bases 

 of the villi, are small glands, the crypts of Lieberkuhn. Each is a 

 simple unbranched tube lined by a layer of columnar cells some of 

 which have a striated free border, though less marked than that 

 on the corresponding cells of the villi, and others are goblet-cells. 

 The crypts of Lieberkuhn are closely packed, side by side, like the 

 glands of the stomach. In the duodenum are found other minute 

 glands, the glands of Brunner. They lie in the submucous coat 

 and send their ducts through the mucous membrane to open on 

 its inner side. 



