THE ABDOMINAL CAVITY 341 



The Iliac Colon descends on the iliacus muscle to the 

 level of the antero-superior iliac spine and then turns medially, 

 parallel to, and a little above,, the inguinal ligament. It forms 

 the medial boundary of the left paracolic gutter and ends, at 

 the brim of the pelvis, by becoming continuous with the pelvic 

 colon. Like the descending colon, the iliac colon is retro- 

 peritoneal and rarely possesses a mesentery. Tumours of the 

 iliac colon are not difficult to recognise, as they may be palpated 

 by rolling the gut against the ilium. Scybalous masses may be 

 distinguished by the fact that they can be pitted on firm pressure. 



The Pelvic Colon, which varies from ten to thirty inches 

 in length, is continuous with the iliac colon above and terminates 

 in front of the third piece of the sacrum, where it becomes 

 continuous with the rectum. It is suspended from the posterior 

 wall of the pelvis by a mesentery, termed the pelvic meso-colon, 

 and consequently is freely movable. The line of attachment 

 of its mesentery resembles an inverted V. It begins on the 

 medial border of the psoas major and passes upwards and 

 medially along the medial side of the external iliac vessels. 

 After crossing the hypogastric (internal iliac) artery, it bends 

 sharply downwards and ends in front of the third sacral vertebra. 

 On account of the arrangement of the mesentery, the terms 

 ascending and descending limbs are used with reference to the 

 pelvic meso-colon and to the parts of the gut which they enclose. 



A small intra- peritoneal fossa, termed the inter sigmoid 

 recess, lies at the apex of the inverted V and is bounded on each 

 side by the left or lower layer of the pelvic meso-colon. This 

 recess is sometimes the site of an intra-peritoneal strangulated 

 hernia. 



The pelvic colon is usually situated partly in the pelvis and 

 partly in the abdomen. When it possesses a long mesentery, it 

 may pass across the median plane, and it is not infrequently 

 seen during the operation of appendicectomy. In the child it 

 lies mainly in the abdomen, owing to the relatively small size 

 of the pelvic cavity. 



The advantage taken by the surgeon of a freely movable 

 pelvic colon is pointed out on p. 343. 



The Inferior Mesenteric Artery arises from the abdominal 

 aorta ij inches above its bifurcation. It runs downwards 

 and slightly to the left, and gives off the left colic (p. 340) 

 and the sigmoid arteries. Its downward continuation into the 

 pelvis is called the superior hcemorrhoidal artery. 



22 b 



