THE LARGE INTESTINE 281 



extremity passes upwards under cover of the costal margin for 

 an inch or more above the transpyloric plane and immediately 

 lateral to the left lateral line (PL II.). 



Above, the transverse colon is related to the stomach, and 

 the interposition of a dull area between the two is suggestive 

 of pancreatic cyst or tumour. 



The Descending Colon is only about 4 inches long and is 

 entirely retro-peritoneal. It extends vertically downwards from 

 the left colic flexure to the iliac crest, and it is placed more 

 deeply in the abdominal cavity than the ascending colon, 

 being separated from the anterior abdominal wall by coils of 

 small intestine. 



The Iliac Colon runs downwards and medially across the 

 left iliac fossa, from the iliac crest to the brim of the pelvis. 

 In its lower portion it lies parallel to and a little above the 

 lateral half of the inguinal ligament (of Poupart). Normally, 

 coils of small intestine intervene between the iliac colon and 

 the anterior abdominal wall, but tumours of this part of the 

 bowel can be palpated when deep pressure is used, owing to 

 the resistance offered by the ilium. 



The Pelvic Colon varies considerably in length, but it 

 always possesses a definite mesentery. It may be as short as 

 6 and as long as 16 inches, and its coils usually lie within 

 the pelvis in relation to the rectum, the bladder and the 

 terminal coils of the ileum. 



The Rectum, which is about 5 inches long, commences 

 opposite the third sacral vertebra, where it is continuous 

 above with the pelvic colon. In its upper third, it is covered 

 with peritoneum anteriorly and on each side; in its middle 

 third, it is covered only on its anterior aspect. At the junction 

 of the middle and lower thirds of the rectum, the peritoneum 

 passes forwards, forming the floor of the pelvic compartment 

 of the peritoneal cavity, and reaches the bladder, in the male 

 (the upper part of the posterior wall of the vagina in the 

 female, Figs. 127 and 134). The lower third of the rectum is 

 therefore devoid of peritoneal covering. 



