142 NORMAL HISTOLOGY. 



The Peyer's patches are most abundant in the lower part of the 

 ileum, where they lie in the intestinal wall opposite the line of 

 mesenteric attachment, and form oval areas with their long axes 

 parallel to the axis of the intestine. 



7. The Colon. The mucous membrane of the colon is destitute 

 of villi, but contains crypts of Lieberkiihn closely arranged side by 

 side and lined with columnar epithelium rich in mucigenous cells. 

 The muscularis mucosse is similar to that of the small intestine, and 

 gives oif occasional fibres that penetrate between the crypts. 



The submucous coat resembles that of the small intestine, and, in 

 common with the mucous membrane, contains solitary lymph-fol- 

 licles, most abundantly in the csecum and vermiform appendix. 



The muscular coat has its outer or longitudinal layer most highly 

 developed in three bands, which are situated about equidistantly 

 around the circumference of the bowel and occasion a pouching of 

 the intervening wall. 



The serous coat is similar to that of the small intestine, but is 

 occasionally extended over small pendulous projections of the 

 subserous fibrous tissue, which contain adipose tissue, appendices 

 epiploicse. 



8. The rectum resembles the colon in its structure, except that the 

 three muscular bands present in the latter are wanting. The mucous 

 membrane as it passes into the anal canal loses its tubular glands, 

 and subsequently becomes covered, not with columnar, but with 

 stratified epithelium, continuous with the epidermis of the skin 

 around the anus. 



9. The pancreas (Fig. 122) has a structure similar to that of the 

 .salivary glands, but its lobules are separated and held in place by a 

 rather more considerable amount of loose areolar tissue, in which 

 there are occasional groups of cells of uncertain nature, but cer- 

 tainly distinct from those lining the glandular acini. They are 

 .called the " interalveolar cell-islets," and may, perhaps, be of the 

 nature of ductless glands (q. v.). 



As the pancreas exercises its secretory function the granules 

 within its cells move toward the lumina of the acini and successively 

 .disappear, the attached ends of the cells becoming clearer and the 

 whole cell diminishing somewhat in size during the process. 



The nerves of the stomach and intestinal tract form two gan- 

 glionated plexuses, the plexus of Auerbach, which lies between the 

 two layers of the muscular coat, and the plexus of Meissner, situ- 



