THE ALIMENTARY CANAL AND ITS APPENDAGES 455 



The Large Intestine (Fig. 136), forming the final portion of the 

 alimentary canal, is about 1.5 meters (5 feet) long, and varies in 

 diameter from about 6 to 4 centimeters (2J^ to 1^ inches). Anato- 

 mists describe it as consisting of the ccecum with the vermiform 

 appendix, the colon, and the rectum. The small intestine does not 

 open into the commencement of the large but into its side, some 

 distance from its closed upper end, and the caecum, CC, is that 

 part of the large intestine which extends beyond the communica- 

 tion. From it projects the vermiform appendix, a narrow tube not 

 thicker than a lead pencil, and about 10 centimeters (4 inches) 

 long. The colon commences on the right side of the abdominal 

 cavity where the small intestine communicates with the large, 

 runs up for some way on that side (ascending colon, AC), then 

 crosses the middle line (transverse colon, TC) below the stomach, 

 and turns down (descending colon, DC) on the left side and there 

 makes an S-shaped bend known as the sigmoid flexure, SF; from 

 this the rectum, R, the terminal straight portion of the intestine, 

 proceeds to the anal opening, by which the alimentary canal com- 

 municates with the exterior. In structure the large intestine 

 presents the same coats as the small. The external stratum of the 

 muscular coat is not, however, developed uniformly around it, 

 except on the rectum, but occurs in three bands separated by in- 

 tervals in which it is wanting. These bands being shorter than 

 the rest of the tube cause it to be puckered, or saccullated, between 

 them. The mucous coat possesses no villi or valvulae conniventes, 

 but is usually thrown into effaceable folds, like those of the stomach 

 but smaller. It contains numerous closely set glands much like 

 the crypts of Lieberkiihn of the small intestine. 



The Ileocolic Valve. Where the small intestine joins the large 

 there is a valve, formed by two flaps of the mucous membrane 

 sloping down into the colon, and so disposed as to allow matters 

 to pass readily from the ileum into the large intestine but not the 

 other way. 



The Nerves of the Intestines. The intestines, like the stomach, 

 have the double autonomic innervation; the paths of approach 

 are in general the same as for the stomach, by way of the vagus 

 for the cranial autonomies, and the splanchnics for the thoracico- 

 lumbar. Both these sets of nerves ramify in the solar plexus; 

 from here nerve strands pass to the intestine, as well as to the 



