THE INTESTINES. 



521 



face of the intestine which is r opposite to the mesentery; they are most 

 distinct upon the inner surface, where they appear as rather depressed, 

 smooth spots, without any very sharp definition, but they are also recog- 

 nizable from the exterior, by the slight elevation to which they give rise; 

 by transmitted light they look like more opaque portions of the mem- 

 brane. These patches are usually most abundant in the ileum, but they 

 are not uncommonly to be met with in the lower part of the jejunum : 

 occasionally they exist in its upper portion close to the duodenum and 

 even in the inferior horizontal portion of the duodenum itself. Ordi- 

 narily there are 20-30 of them; when they are found higher up there 

 may be as many as 50-60 ; but they are 

 always most closely set in the lowest 

 portion of the ileum. The dimensions 

 of the separate patches are in general 

 the larger, the closer they are to the cce- 

 cum; their length is usually 5-1 J lines, 

 but may diminish to 3 and increase to 

 3-5 lir>es, or even 1 inch ; their breadth 

 varies from 3 to 5 or 9 lines. Where 

 the patches lie, the valvulce conniventes 

 are usually interrupted; in the jejunum, 

 however, these folds are also to be met 

 with ; upon the Peyer's patches and in the 

 ileum, rows of closely set villi often take 

 their place. 



More minutely examined, every Pey- 

 er's patch is seen to be an aggregation 

 of closed follicles, of 1-6-1-2-1 line in 

 diameter, either rounded or slightly co- 

 nical towards the intestinal cavity, which lie partly in the mucous mem- 

 brane itself, partly in the submucous tissue, and are, on the one side not 

 more than 0-02-0-03 of a line distant from the 

 mucous surface, while on the other, they are in 

 immediate contact with the muscular tunic, which 

 is here somewhat more closely united with the 

 mucous membrane. Viewed from the interior of 

 the intestine, their most striking feature in Man 

 is the presence of many small rounded depres- 

 sions j J-l line apart, which correspond with 

 the separate follicles, and whose floor is, indeed, 



FIG. 213. A Peyer's patch (Man), magnified 4 diameters: a, ordinary mucous surface, 

 with villi; 6, depressions upon the patches corresponding with the follicles; c, intermediate 

 substance, with small villi. 



FIG. 214. Portion of a Peyer's patch of an old Man, after Flouch : a, follicle, surrounded 

 by the apertures of the Lieberkuhnian glands; 6, villi; c, more isolated Lieberkuhnian 

 follicles. 



Fiar. 214. 



