368 



THE DIGESTIVE SYSTEM 



Villi are found upon the free surface of the agminate nodules only 

 in the intervals between the constituent units. The largest of the 

 nodules lie near the center of the patch, the smallest are found at its 

 periphery. The agminate nodules become the chief seats of infection in 

 typhoid fever. 



Above the level of the ileum the largest collections of lymphoid 

 tissue in the intestinal mucosa occur in the upper part of the duo- 

 denum, where there are extensive infiltrations of dense lymphoid tissue, 

 many of which contain typical nodules with germinal centers. These 



masses of lymphoid tissue are 

 penetrated by the ducts of the 

 duodenal glands, whose secret- 

 ttetit ing portions form a bed upon 

 which the lymphoid tissue 

 ,tiaaf re sts. The duodenal patches 

 differ slightly from those in 



FIG. 



m orc confluent mass with rela- 

 343,-DiAGRAM OF SMALL INTESTINE, tively fewer nodules ; they also 



SHOWING THE TOPOGRAPHICAL RELATION- possess a more diffuse charac- 

 SHIP OF THE INTESTINAL GLANDS (CRYPTS * , , ., , , 



OF LiEBERKtJHN) TO THE VILLI. ter, are more deeply situated, 



and are therefore covered by 

 the corium of the mucosa which contains both intestinal glands and 



vim. 



THE INTESTINAL VILLI. The intestinal villi are long finger- 

 like projections (from 0.5 to 1 millimeter in length) which vary 

 much in form in different mammals and in different portions of the 

 canal in the same individual. They are perhaps most highly developed 

 in the dog, where they form long projections with expanded or clubbed 

 extremities and a constricted base or neck. 



In man the villi are of a more conical shape, the base being, as a 

 rule, slightly broader than the free extremity. In the duodenum of 

 man they possess a foliate shape, in the jejunum they are conical or 

 somewhat clavate, in the ileum they are generally filiform. The villi 

 are most abundant in the duodenum and the jejunum (24 to 40 per 

 square millimeter) and less numerous in the ileum (15 to 30 per square 

 millimeter) (Piersol). According to Johnson (Amer. Jour. Anat., 14, 

 2, 1913) they are more or less variable structures, their shape and 

 height changing with the degree of distention of the tube. 



