92 



SPECIAL HISTOLOGY. 



a great number of permanent folds and villi ; also, imbedded 

 Fig. 206. in its substance, peculiar closed fol- 



licles, the so-called solitary and 

 Peyer's glands and, in the sub- 

 mucous tissue of the duodenum, 

 Brunner's glands. 



The mucous membrane consists 

 of connective tissue, which is in- 

 ternally homogeneous or indis- 

 tinctly fibrillated ; except where 

 certain glands exist, there is but 

 little submucous tissue, so that it is 

 pretty closely connected with the 

 muscular tunic. Upon the inner 

 surface of the mucous membrane, 

 there rests a cylinder epithelium, 

 to which further reference will be 

 made under the head of the villi ; 

 e whilst externally, towards the sub- 

 mucous tissue, it is bounded by a 

 . layer of smooth muscles, discovered 

 by Brucke, which measures, at most, 

 0*01 11'"', they are disposed longitu- 

 dinally and transversely, but in man 



their slight development renders it often very difficult to 



discover them. 



§ 153. 



The villi of the small intestine are small, whitish elevations 

 of the innermost portion of the mucous membrane, readily 

 distinguishable with the naked eye and which, distributed upon 

 and between the valvule conniventes {Kerkringian valves) 

 through the whole extent of the small intestine, from the pylorus 

 to the sharp edge of the ileo-csecal valve (valvula Bauhini), 

 are set so close together as to give the mucous membrane its 

 well-known velvety appearance. They are most numerous 



Fig. 206. Section through the walls of the lowest portion of a Calf's ileum, x 60 : 

 a, villi ; b, Lieberkuhn's glands ; c, muscular layer of the mucous membrane ; d, 

 follicles of a Peyer's patch ; e, remainder of the submucous tissue under them ; /, 

 circular muscles ; g, longitudinal muscles. 



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