THE DIGESTION OF FOOD 



115 



169. Function of lacteals and blood vessels in absorp- 

 tion (Figs. 4, 5).— A merely casual observation shows us 

 that the inner surface of the walls of the small intestine is 

 covered by numerous projections, called villi. In these are 

 imbedded the minute branches of two systems of vessels, 



Fia. 4. Cross-seotipn of mucous membrane of small intestine of man, 

 showing oapillailes and lacteals. (Gerrish.) 



the lacteals, belonging to the so-called lymphatic system, 

 and the capillaries, which are minute branches of the 

 blood system. The lacteal is in the center of each villus 

 and this is surrounded by a network of capillaries. The 

 lymphatic vessels lead to a main tube or reservoir, the 

 thoracic duct, which extends along the spinal column 



