336 THE ABDOMEN AND PELVIS 



middle line where, in the supine position, it lies at or a little 

 below the umbilicus. In many cases, however, the transverse 

 colon is placed at a much lower level, and its position depends 

 on (i) its length, which may be greatly increased, e.g. in cases 

 of undescended caecum (p. 346), and (2) the length of the 

 transverse meso-colon. 



In the erect posture the transverse colon descends still 

 further, and is often seen lying behind the pubic symphysis. 

 Under these circumstances, the right and left colic flexures 

 become very acute, and the proximal part of the transverse 

 colon descends in front of or medial to the ascending colon. 

 If these two pieces of bowel are attached to one another 

 by peritoneal bands (p. 334) or adhesions, the kinking will 

 persist in the supine position and may give rise to delayed 

 peristalsis and chronic constipation. 



The transverse colon is completely surrounded by peritoneum 

 except along narrow strips on its upper and lower surfaces, 

 where the transverse meso-colon and the greater omentum reach 

 the gut (Fig. 85). 



The transverse meso-colon suspends the transverse colon 

 from the posterior abdominal wall. It is attached normally 

 to the front of the head, neck, and body of the pancreas, but it 

 may extend further over to the right and cross the anterior 

 surface of the second part of the duodenum. It separates the 

 cavity of the omental bursa from the infra-colic compartments 

 (Fig. 85), and is related to the stomach, anteriorly, and to the 

 duodeno-jejunal flexure and coils of small intestine, posteriorly. 

 The two layers of the transverse meso-colon contain the middle 

 colic vessels, lymphatics, and nerves. 



The BLOOD-SUPPLY to the ascending colon, right colic flexure, 

 and the transverse colon is derived from (i) the right and (2) 

 the middle colic branches of the superior mesenteric artery. 



(1) The right colic artery, which often arises by a common 

 trunk with the ileo-colic, runs to the right, behind the peritoneum 

 of the right infra-colic compartment. It crosses in front of the 

 right psoas major, ureter, and spermatic vessels, and usually 

 lies a little below the right kidney. Near the gut it divides 

 into a descending branch, which anastomoses with the colic 

 branch of the ileo-colic, and an ascending branch, which 

 anastomoses with the right division of the middle colic. Both 

 branches supply the ascending colon (Fig. 106). 



(2) The middle colic arises from the superior mesenteric at 



