THE ALIMENTARY CANAL 



379 



rectum and in the vermiform appendix. In the latter the nodules are 

 more or less confluent, a condition which is not found elsewhere in 

 the large intestine. In the appendix the greater portion of the mucous 

 membrane is invaded hy lymphoid tissue, and the glands are much 

 diminished in hoth number and size (Fig. 352). 



The Vascular and Nerve Supply. The vascular and nerve supply 

 of the large intestine is 

 identical in its arrangement 

 with that of the small intes- 

 tine. The mucous mem- 

 brane contains a capillary 

 plexus of blood and lym- 

 phatic vessels in the corium 

 about the glands. The 

 nerves of the large intestine 

 include both mcdullated and 

 non-medullated fibers. The 

 latter supply its muscular 

 coats and blood-vessels. The 

 former end in naked vari- 

 cose or knobbed fibrils be- 

 neath and upon the epithe- 

 lium of the glands. The 

 usual myenteric ( Auer- 

 bach's) and submucous 

 (Meissner's) plexuses ap- 

 pear in the large intestine 



with the same structure and location as elsewhere in the alimentary 

 canal. 



In the rectum the lining epithelium is continuous at the anus with 

 the stratified squamous epithelium of the skin. In this region also, 

 the circular fibers of the inner layer of the muscular coat are much 

 thickened to form the internal rectal sphincter. Lymphoid tissue 

 abounds in the rectal mucous membrane. The glands are less numerous 

 but larger than in the colon proper, and the mucosa is thicker. In the 

 lower portion of the rectum the mucosa is thrown into a number of 

 longitudinal folds, the rectal columns, at which level the columnar 

 epithelium changes to stratified squamous type. 



The Ileocecal (Colic) Valve. The ileocecal valve, which guards 

 the orifice by which the small intestine opens into the large, is formed 



FIG. 351. SECTION OF PORTION OF LAKGE INTES- 

 TINE OF DOG, SHOWING THE INTESTINAL 

 GLANDS (CRYPTS OF LIEBEBKUHN) CUT 

 ACROSS, THEIR LINING INCLUDING COLUMNAR 

 AND GOBLET CELLS. 



