102 



SPECIAL HISTOLOGY. 



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 caecum; their length is usually 

 5'"— II", but may diminish to 3'", 

 and increase to 3 — 5" , or even 

 1', their breadth varies from 3"' 

 to 5'" or 9"'. Where the patches 

 lie, the valvules conniventes are 

 usually interrupted ; in the jeju- 

 num, 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 

 Peyer's patch is seen to be an 

 aggregation of closed follicles, of g — \ — Y" in diameter, either 

 rounded or slightly conical towards the intestinal cavity, which 

 lie partly in the mucous membrane it- 

 self, partly in the submucous tissue, 

 and are, on the one side not more than 

 002 — 003"' 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 mem- 

 brane. Viewed from the interior of the intestine, their most 

 striking feature in Man is the presence of many small rounded 

 depressions £'" £'" — V" apart, which correspond with the separate 

 follicles, and whose floor is, indeed, rendered slightly convex 



Fig. 214. 



mm 



\ 9 M 



Fig. 213. A Peyer's patch (Man), x 4: a, ordinary mucous surface, with villi; b, 

 depressions upon the patches corresponding with the follicles ; c, intermediate sub- 

 stance, with small villi. 



Fig. 214. Portion of a Peyer's patch of an old Man, after Flouch : a, follicle sur- 

 rounded by the apertures of the Lieberkuhnian glands ; b, villi ; e, more isolated 

 Lieberkuhnian follicles. 



