314 



COMPARATIVE ANATOMY 



Each villus is covered with a mucus epithelium containing numerous 

 goblet-cells, and each villus has a core of connective tissue filled with 

 capillaries and lymph vessels. A single lymphatic or lacteal occupies the 

 center of each villus, and a network of capillaries lies just below the base- 

 ment membrane of the mucous epithehum. Each villus is therefore a 

 mechanism admirably adapted for absorbing the digested food which 



ViUi. 



Plica circularis. 



Intestinal gland: 



Submucosa. 



Submucosa. A" ^ 



Circular muscle 



Longitudin 

 muscle. 

 Serosa 



Fig. 263. — Vertical longitudinal section of the jejunum of an adult man. The 

 plica circularis on the right supports two small solitary nodules, which do not extend 

 into the submucosa; one of them exhibits a germinal center, x. The epithelium is 

 slightly loosened from the connective tissue core of many of the villi, so that a clear 

 space, XX, exists between the two. The isolated bodies lying near the villi (more 

 numerous to the left of the plicae circulares) are sections of villi that were bent, so that 

 their ends were cut off in sectioning. X16. (From Bremer's "Text Book of Histology.") 



bathes it. Besides the peristaltic waves which pass along the intestine 

 squeezing the food backwards towards the large intestine, divisive or 

 churning movements are also carried on, bringing the digested food into 

 contact with the villi. 



Absorption takes place in the small intestine, in accordance with the 

 law of osmosis. The dissolved foods pass through the lining membranes, 

 are taken up by the blood capillaries and the lymphatics, enter the 

 general circulation, and are absorbed into the cells of the various tissues. 



The Large Intestine. The large intestine or colon differs from the 

 small not only in its great diameter but also in the absence of villi in the 



