1670 



HUMAN ANATOMY. 



especially with short mesenteries, can hardly vary much from a simple loop ; under 

 opposite conditions, however, they may present the most diverse forms, so that a 

 definite shape can hardly be assumed. The M-form is common. We have seen 

 the sigmoid disposed in three parallel vertical folds occupying all of the left iliac 

 fossa and overhanging the true pelvis. As the sigmoid flexure descends along the 

 sacrum it usually curves to the right and crosses the median line. 



Peritoneal Relations. — The lower part of the ascending colon is very 

 often, for one or two inches, completely surrounded by serous membrane. The 

 ligaments of the colon (described with the retro-colic fossa, page 1667) occur more or 

 less well marked at the line where the peritoneum leaves the posterior wall. Above 

 this the colon is connected by areolar tissue to the kidney. Occasionally the colon 

 is adherent as far as the caecum. The non-peritoneal portion of the upper part of 

 the ascending colon equals about one-third of its circumference. 



The transverse colon is attached to the transverse mesocolon and otherwise 

 completely surrounded by peritoneum. The transverse mesocolon, after attaining 

 its permanent condition, arises along the back of the abdomen from one kidney to 



Fig. 1419. 



Anterior band 



Rectum 



Bladder 



Anterior abdominal wall turned 

 forward 



Sigmoid flexure 

 pulled up 



Mesenter>' of 

 sigmoid 



Anterior superior 

 spine of ilium 



Recto-vesical fold 



Sigmoid flexure and rectum ; sigmoid has been displaced upward to show its mesentery. 



the Other. It crosses the front of the right kidney, the second part of the duo- 

 denum, and passes along the lower border of the pancreas above the duodeno-jejunal 

 flexure, to end on the left kidney. Sometimes in the left part of its course its 

 origin rises onto the superior anterior surface of the pancreas. Its greatest breadth 

 — /.<?., the distance from its origin to insertion — is at the middle, and varies from 

 10—15 cm. The posterior layer of the greater omentum fuses with it. The phreno- 

 colic ligament, which runs inward, shelf-like, from the left abdominal wall under the 

 spleen, although in acquired relation with the mesentery of the transverse colon, is 

 really a part of the greater omentum. The latter hangs down from the transverse 

 colon over the small intestine, but its relation to the colon is not the same through- 

 out. On the right it is fused with the peritoneum of the anterior surface of the gut 

 and leaves it at the lower border. On the left it leaves the upper surface of the 

 colon, or even the transverse mesocolon, before the latter reaches the gut. Thus 

 the line at which it leaves the intestine rises gradually from right to left. 



The descending colon is usually uncovered posteriorly by peritoneum. 

 According to Lesshaft,' whose results have been generally accepted, it has more or 

 less of a mesentery once in six times. According to Symington,' the mesenteries 



' Reichert and Du Bois-Reymoiid's Archiv, 1870. 



' Journal of Anatomy and Physiology, vol. x.wi., 1892. 



