134 ABSORPTION 



and the food which they collect from the intestine they 

 convey, by a conamon duct, to a large vein at the base 

 of the neck, and place in the blood circulation at that 

 point. In either case the ultimate disposal of the food 

 is the same, namely, the putting it into the blood. The 

 knowledge of the relation of these collecting blood vessels 

 and lymphatics to the alimentary canal is important to 

 the imderstanding of the method of transfer. 



In the study of the structure of the stomach and intes- 

 tine it was noted that beneath the lining of the mucous 

 membrane and separating it from the muscle layers was 

 a coat of tissue called the submucous layer. 



Further, it was noted that blood vessels entered this 

 layer thi-ough a fold of the peritoneum and within the 

 layer spread out over the mucous lining in a many branched 

 network of fine tubes or capillaries. These tiny, thin 

 walled capillaries, which are thus in contact with the 

 mucous membrane in all parts of the intestine and stomach, 

 are the direct receivers of the digested food of these tracts. 

 These capillaries are all connected and finally fuse into a 

 single large vein called the portal vein. 



Again, we may recall that the lining of the small intes- 

 tine was not smooth, except in appearance, and that the 

 surface of the mucous lining was raised in tiny projections 

 called villi. (See p. 120.) A lengthwise section of one of 

 these villi (see Fig. 46) shows the following structure: 

 Each villus is seen to be a tiny conical projection of the 

 mucous membrane (one fiftieth to one eighth of an inch in 

 length). The outside, or surface exposed to the digestive 

 fluids, is composed of a single layer of mucous membrane 

 cells, while the core of the villus is a loose network of 

 blood capillaries and connective tissue cells, together with 



