CHAP. XXV.] THE INTESTINAL CANAL. 217 



this forms the right or ascending colon ; at the liver it turns to the 

 left, and passes, in arched form, across the abdomen from the right 

 to the left hypochondrium, thus forming the transverse colon, or the 

 arch of the colon; it then turns downward, passes through the left 

 lumbar region to the left iliac fossa ; this portion, which is straight 

 or nearly so, is the left or descending colon. In the left iliac fossa 

 the intestine becomes somewhat curved, and is rather loosely 

 attached to the wall of the pelvis; its curve resembles the letter S; 

 this portion terminates in the pelvis, and is named the sigmoid 

 flexure of the colon; lastly, this becomes continuous with the 

 pelvic or terminal portion of the intestine, which, although far 

 from being straight, is designated intestinum rectum, or commonly 

 the rectum. This opens externally at the anus, its mucous mem- 

 brane becoming continuous with the skin at that orifice. 



The small intestine is arranged in many convolutions, and, with 

 the exception of its upper portion, the duodenum, it is quite loose in 

 the cavity of the abdomen, and even in that of the pelvis, occupying 

 the central part of those cavities. The large intestine or colon 

 embraces it on the right, above, and on the left. Three portions of 

 the small intestine have always been recognised by anatomists, 

 which, although not distinguished by any well-marked external 

 boundaries, exhibit in their mucous membrane features (to be 

 pointed out hereafter) which form their most appropriate means of 

 distinction. The upper portion is sufficiently distinct from the 

 rest by its dilated form, its horse-shoe curve, and by being closely 

 fixed to the spine, in the greatest part of its extent, by peritoneum. 

 This is the duodenum : it forms about the first twelve inches of the 

 small intestine. 



The middle portion of the small intestine is the jejunum, and the 

 terminal portion is the ileum. These have no external mark to 

 distinguish the one from the other. The jejunum is wider than the 

 ileum, and its coats are thicker; the intestine tapers as it approaches 

 the ccecum. 



The whole intestinal tube is more or less completely covered 

 by the serous membrane of the abdomen, the peritoneum* The 

 duodenum above and the rectum below, are least covered by it; 

 the rest is almost entirely enveloped, a small portion being left 

 uncovered where the blood-vess'els enter the intestine, and where 

 the peritoneum passes to the abdominal wall. Each portion 

 of intestine is attached to the abdominal wall by a process of 

 peritoneum, the duodenum and the rectum very closely, the rest 

 more or less loosely. The process of peritoneum which connects 



VOL. II. Q 



