282 



THE DIGESTIVE ORGANS. 



In the colon the villi are wanting, while the glands of the 

 mucosa are densely placed and distributed with regularity. 



The glands of Lieberkiihn in the colon are somewhat longer, 

 and as a rule contain many more goblet cells than those in the small 

 intestine. Only the neck and fundus of the glands show cells de- 

 void of mucus. Transitional stages between the latter and the 

 goblet cells have been observed in man (Schaffer, 91). Solitary 

 lymph-follicles are found throughout the colon. They are situated 

 in the mucosa, only the larger ones extending into the submucosa. 

 The glands of Lieberkiihn are displaced in the regions of the lymph- 

 follicles. 



Gland. 



Submu- 

 cosa. 



Fig. 222. A solitary lymph-follicle from the human colon : At a is seen a pronounced 

 concentric arrangement of the lymph-cells. 



The tanice and plica semilunarcs cease at the sigmoid flexure, 

 and are replaced in the rectum by the plica transversales recti. 

 Permanent longitudinal folds, the so-called columns rectales Mor- 

 gagni, are present only in the lower portion of the rectum. Here the 

 intestinal glands are longest but disappear simultaneously with 

 the rectal columns. At the anus the mucous membrane of the 

 rectum forms a narrow ring devoid of glands, covered by stratified 

 pavement epithelium, and terminating in the skin in an irregular 

 line. The transition from the mucous membrane to the skin is 

 gradual, yet reminding one of the appearance presented at the 

 junction of the esophagus with the cardiac end of the stomach. 



External to the anus, and at a distance of about one centimeter 

 from it, are numerous highly developed sweat-glands, the circum- 

 anal glands of Gay, which are almost as large as the axillary 

 glands ; also sweat-glands of a peculiar type, in that they show a 

 branching of the tubules (see Sweat-glands, under Skin). 



