THE DIGESTIVE ORGANS. 



141 



lymph -follicles may be regarded as the result of an increase in the 

 amount of reticular tissue of the villus, which has replaced the 

 other structures usually present. In the lower portions of the 

 small intestine there are collections of these solitary follicles, 

 which have received the name u Peyer's patches. 7 ' 



6. The small intestine below the duodenum resembles the latter 



FIG. 121. 



Section of solitary follicle from the ileum. (Cadiat.) a, space left by the disintegration of 

 the central, delicate lymphadenoid tissue of the follicle during the preparation of the sec- 

 tion ; b, columnar epithelium of intestinal surface ; c, c, villi, partially denuded of epithe- 

 lium; d, crypt; e,f, muscularis mucosae; above /, the point where the vessels enter the 

 follicle. The Peyer's patches are collections of such solitary follicles, placed side by side 

 and destitute of villi at their upper surfaces. 



in structure, with a few modifications, which become progressively 

 more marked as the distance from the stomach increases. 



The glands of Brunner are most abundant near the upper part 

 of the duodenum, more sparsely distributed further down, and 

 usually disappear entirely before the beginning of the jejunum. 



The valvulse conniventes, which are most highly developed a 

 little below the entrance of the gall and pancreatic ducts, also 

 become lower and less frequent along the course of the intestine, 

 and finally disappear about the middle of the ileum. 



The crypts of Lieberkiihn are deepest in the upper part of the 

 intestinal tract, but persist in shallower form throughout its whole 

 extent, as well as along the whole length of the colon. 



