92 PHYSIOLOGY. 



fibers of the muscularis mucosa and a single lacteal or lymphatic 

 vessel. The body of the villus is composed of adenoid tissue, closely 

 invested with small and numerous bundles of smooth muscular fibers 

 arranged in a longitudinal and in an oblique direction, and derived 

 from the muscularis mucosa. 'The longitudinal fibers, when they 

 contract, shorten the villus and with the valves in the lacteal empty 

 it, whilst the oblique fibers keep the lacteal open. These muscular 

 fibers are attached to the sub-epithelial basal membrane. The 

 lymph-spaces in the adenoid tissue form a network of channels com- 

 municating with each other, and contain leucocytes and fine globules 

 of fat, which have passed through the spaces between the epithelial 



Fig. 22. Mucous Membrane of the Jejunum, Highly Magnified, 

 (schematic). (TESTUT, RAYMOND.) 



1, 1, Intestinal villi. 2, 2, Closed or solitary follicles. 3, 3, Orifices of the 

 follicles of Lieberkiihn. 



cells on the border, then through the basal membrane, through the 

 lymph-spaces of the parenchyma of the villus, and finally enter the 

 lacteal. The lymph-vessels end in the upper part of the villus, in 

 a blind extremity, and show a certain degree of anastomosis, and when 

 joined form the central chyle-vessel or lacteal. The lacteal lies 

 in the center of the villus, whilst the artery enters to one side of it 

 and spreads out into a network of capillaries, like an umbrella, over 

 the lacteal immediately underneath the epithelium of the villus. The 

 number of the villi has been estimated to be about four millions. 



