342 THE HUMAN BODY. 







and send their ducts through the mucous membrane to open 

 on its inner side. 



The Large Intestine (Fig. 120), forming the final por- 

 tion of the alimentary canal, is about 1.5 meters (5 feet) 

 long, and varies in diameter from about G to 4 centimeters 

 (2^ to 1 inches). Anatomists describe it as consisting of 

 the ccecum with the vermiform appendix., the colon, and the 

 rectum. The small intestine does not open into the com- 

 mencement of the large but into its side, some distance from 

 its closed upper end, and the ca3cum, CO, is that part of the 

 large intestine which extends beyond the communication. 

 From it projects the vermiform appendix, a narrow tube 

 not thicker than a cedar 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, 

 TO) 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 communi- 

 cates 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 intervals in which it is wanting. These bands 

 being shorter than the rest of the tube cause it to be puck- 

 ered, or sacculated, between them. The mucous coat pos- 

 sesses no villi or valvula3 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 Ileo-colic 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. These, like those of the 

 heart with which we shall later have to compare them 

 physiologically, are intrinsic and extrinsic. The former are 

 connected with small ganglia found abundantly on the 



