ABSORPTION DIGESTION COMPLETED. 185 



tacle of the chyle, or the beginning of the main lymph vein (thoracic 

 duct), should be found. Trace it anteriorly through the chest along- 

 side the aorta to its mouth, near the junction of the left subclavian and 

 jugular veins. 



Action of the Villi. In each villus there are plain 

 muscle fibers. When these shorten they squeeze the 

 chyle, that has already been absorbed, into the lymph 

 tubes of the wall of the intestines, and on into the main 



Epithelial Covering 



Lacteal 



Longitudinal Mus- 

 cular Fibers 



Capillary Network 



r-i-i ; '-juy 



E322SSSBHE3J, 



Fig. 68. Intestinal Villus. 



lymph duct. The chyle cannot return to the lacteal when 

 the muscles relax, on account of the valves, similar to 

 those of the veins, in the lacteal at the base of the villus. 

 Then, when the muscles relax, the lacteal is empty, and 

 ready to absorb more of the emulsified fat that we call 

 chyle. 



Review of the Digestive Tube. The whole digestive 

 tube may be briefly and roughly described as a muscular 

 tube of varying diameter, lined by mucous membrane. 

 The muscular coat propels the contents and mixes them 

 with liquids ; the mucous coat is beset with glands, making 

 liquids, some of which merely soak the food, others act 

 on it chemically, while mucus serves to lubricate the sur- 

 face. It seems that these myriads of simple glands are 

 not enough, so several large compound glands lie along- 

 side the food tube and empty their secretions into it by 



