45 2 THE ALIMENTARY CANAL. [CH. xxvil. 



passes through the muscularis mucosse, and opens on the surface 

 of the mucous membrane. 



Peyer's patches are found in greatest abundance in the lower 

 part of the ileum near to the ileo-caecal valve. They consist of 

 aggregated groups of lymphoid nodules ; they vary from one 

 to three inches in length, and are about half-an-inch in width, 

 chiefly of an oval form, their long axes being parallel with that 

 of the intestine. They are almost always placed opposite the 

 attachment of the mesentery. 



When the lymphoid nodules occur singly, as they often do 



Fig. 386. Agminate follicles, or Peyer's patch, in a state of distension, x 5. (Boehm.) 



both in small and large intestines, they are called solitary glands, 

 or follicles. 



The Large Intestine. The Large Intestine, which in an 

 adult is from about 4 to 6 feet long, is subdivided for descriptive 

 purposes into three portions, viz. : the caecum, a short wide 

 pouch, communicating with the lower end of the small intes- 

 tine through an opening, guarded by the ileo-ccecal valve ; the 

 colon, continuous with the caecum, which forms the principal part 

 of the large intestine, and is divided into ascending, transverse, 

 and descending portions ; and the rectum, which, after dilating 

 at its lower part, again contracts, and immediately afterwards 

 opens externally through the anus. Attached to the caecum is the 

 small appendix vermiformis. 



Structure. Like the small intestine, the large intestine is con- 

 structed of four coats, viz., the serous, muscular, sub- mucous, 

 and mucous. The serous coat has connected with it the small 

 processes of peritoneum containing fat, called appendices epiploicae. 

 The fibres of the muscular coat, like those of the small 

 intestine, are arranged in two layers the outer longitudinal, 



