606 



THE DIGESTIVE TRACT. 



maintained, in no way connected with the chyliferous vessels. 

 The submucous portion of the vermiform appendage has a very 

 broad layer of lymph-tissne. While the muscle of the small intes- 

 tine is almost uniformly distributed throughout the tube, and the 

 circular always shows greater development than the longitudinal ; 

 in the large intestine, on the contrary, the outermost longitu- 

 dinal muscle-layer is imperfectly developed, but in certain places, 

 called tcenice, accumulates in ribbons. At the point of the junc- 

 tion of the ileum and coecum the circular muscle-layer enters 

 the formation of the valvula Bauhini, while the longitudinal 

 layer directly passes from the small to the large intestine. 



FIG. 260. RECTUM OF A DOG. VERTICAL SECTION 

 IN THE LONGITUDINAL Axis. 



F, columnar epithelium; A, acinous mucous glands; MM, longitudinal muscle-layer of 

 the mucosa ; C, submucous fibrous connective tissue ; MI, circular muscle of the intestine, in 

 transverse section. Magnified 300 diameters. 



The mucosa of the rectum exhibits reduplications like that of 

 the large intestine, and is, in its lower portions, supplied with a 

 varying number of racemose glands, especially well developed in 

 the rectum of the dog. (See Fig. 260.) The internal sphincter is 

 constituted by an aggregation of the smooth circular muscle- 

 fibers, while the external sphincter is composed of striated mus- 





