220 



ABSORPTION VILLI. 



Caval Veins 



Again, while the folds in the lining of the stomach are 

 temporary, these are permanent. They serve to increase the 

 surface of the lining, and to retard the passage of the food 

 material, and so to aid the process of digestion and of absorp- 

 tion. 



Further, the surface of the mucous membrane is thickly 

 beset with little cylindrical projections, like the "pile" on 



velvet. These pro- 

 jections are called 

 Yilli (singular, vil- 

 lus). Thevilli 

 greatly increase 

 the absorbing sur- 

 face of the small 

 intestine. In each 

 villus is a network 

 of Blood Capil- 

 laries, and the 

 beginning of 

 lymphatic capil- 

 laries called Lac- 

 teals. 



In the villi 

 the largest part 

 of the work of 

 absorption is 

 done. The fats 

 are absorbed by 

 the lymph capil- 

 laries, and the rest of the foods by the blood capillaries. It 

 should be carefully noted that nearly all of the foods but the 

 fats go at once to the liver, through the portal vein ; but the 

 fats are carried by the main lymph duct (the Thoracic Duct) 



- Portal Vein 



Mesenteric 



Blood Veins 



(Albumen 



Sugar) 



Capillaries 



Fig. 65. Plan of Absorption. 



