THE ABSORPTION OF FOODS 



113 



FIG. 60. APPEARANCE OF THE 

 INTERIOR OF THE INTESTINE 

 Showing the folding of its lining. 



testine is practically a tube within a tube, the outer of which 

 is for the most part muscular. If we imagine the inner tube 

 to be longer than the outer, the 



inner tube will consequently be g r __,-.^...- .. - -. .^-^..- : .. ._. y~ - .* ^ 

 thrown into ridges which go trans- 

 versely around it, intruding on the 

 cavity more or less. Some but not 

 all of the ridges will pass entirely 

 around the tube ; Fig 60. Further- 

 more the whole lining, ridges and 

 all, is covered with minute, flex- 

 ible projections, almost as if 

 there were tiny fingers protruding 

 into the food mass of the intestine. 

 These fingers are called villi, and 

 they take the food from the intestine by a method of their 

 own. They are just long enough to be 

 seen with the naked eye; Fig. 61. 



Into each villus extends a nerve and 

 also a tiny branch of one of the arteries 

 in the intestinal walls. This arteriole 

 extends nearly to the end of the villus 

 and there breaks up into much smaller 

 blood vessels, which thus form a sort of 

 network; Fig. 62. After passing through 

 this network and picking up food in a 

 manner to be described presently, the blood 

 returns again through veins to the intes- 

 tinal wall and is then carried off once more 

 into the body. Each villus contains 

 another tube also (Fig. 61), called a lacteal, 

 which receives the fats of the food. A 

 single layer of cells, the epithelium, covers 

 each villus and separates the blood vessels 

 and lacteals from the liquid contents of the intestine. 



FIG. 61. A SINGLE 

 VILLUS 



Highly magnified. 



