I 74 



NORMAL HISTOLO 



in some cases also in man, the follicles 

 zone of adenoid tissue. 



ae, li 



FIG. 215. 



continuous 



The muscularis mucosae, like that of the stomach, occupies the 

 deepest part of the mucosa and marks the outer boundary of the 

 mucous layer. The muscular tissue comprises longitudinally-dis- 

 posed bundles of muscle-cells, supplemented in some places by a 

 more or less complete additional internal layer of circularly-placed 

 cells. 



The submucosa of the intestinal wall corresponds to the similar 

 coat of the stomach, consisting of loosely-united bundles of fibro- 



elastic tissue, which support 

 the larger vascular and lym- 

 phatic trunks, as well as a rich 

 nervous plexus. 



The muscular coat con- 

 sists of two well-developed 

 layers the thicker inner cir- 

 cular and the less robust 

 outer longitudinal stratum. 

 These are separated by a thin 

 layer of connective tissue, 

 which externally becomes 

 continuous with the envel- 

 oping areolar tissue and passes 

 into the outer fibrous tunic of 

 the serosa. 



In parts of the large intes- 

 tine as the caecum and the 

 colon the circular muscular 

 coat is relatively thin, while 

 the longitudinal layer is in- 

 complete, the fibres of the lat- 

 ter being collected into three 

 flat bands, 1015 mm. wide; 

 these longitudinal bands are 

 much shorter than the other 

 layers of the intestinal wall, 

 which arrangement results in 

 the characteristic sacculation 

 of the large intestine. In the 

 lower part of the rectum the circular muscular layer becomes thick- 

 ened to form the internal anal sphincter, composed of involuntary 

 muscle ; the bands of longitudinal fibres spread out, and towards the 

 lower end of the rectum form a thick, uniform layer. 



Section of injected small intestine of cat : a, b, mu- 

 cosa ; g t villi ; i, their absorbent Vessels ; h, simple 

 follicles ; c, muscularis mucosae ; d, submucosa ; e, e' , 

 circular and longitudinal layers of muscle ; f t fibrous 

 coat. All the dark lines represent blood-vessels filled 

 with the injection mass. 



