496 ABDOMEN 



at the termination of the descending colon at the level of the 

 upper and back part of the iliac crest. It passes downwards 

 and forwards to the region of the anterior superior iliac 

 spine, and then turns medially, along the line of the inguinal 

 ligament, to the brim of the small pelvis, where it becomes the 

 pelvic colon. Its length is variable, but averages about six 

 inches. It does not possess a mesentery, but is covered with 

 peritoneum anteriorly and along its sides. Posteriorly it is 

 separated by the extra-peritoneal fat from the iliacus, the 

 psoas magnus, the femoral nerve (O.T. anterior crural) which 

 lies in the groove between the two muscles, and its termina- 

 tion is in front of the left external iliac artery. 



The remaining portions of the large intestine will be 

 considered in association with the dissection of the pelvis. 



Dissection, Place two ligatures round the descending colon, below the 

 splenic flexure, and two more ligatures round the junction of the iliac with 

 the pelvic colon ; divide the intestine between each pair of ligatures and 

 remove the descending and the iliac portions of the colon. Take the 

 detached intestine to the sink, wash it thoroughly, open it, and note that, 

 as in the other parts of the large intestine previously examined, the mucous 

 membrane is devoid of villi and of plicae circulares. After the separated 

 part of the intestine has been examined, clean the posterior wall of the 

 abdomen in the regions from which it was removed and then expose the 

 structures which form its posterior relations. After these have been 

 displayed clear away the remains of the transverse meso-colon from the 

 front of the pancreas and proceed to the examination of the duodenum. 



Duodenum (The Duodenum). It has already been noted 

 that the duodenum is the first part of the small intestine, and 

 it would have been examined, in proper sequence, immediately 

 after the examination of the stomach, had it not been that a 

 complete examination of it at that time would have interfered 

 too much with the relations of other portions of the intestine 

 which have now been removed. The duodenum is from ten to 

 twelve inches in length, it is the widest and the most fixed 

 of the three parts of the small intestine, and its walls are 

 thicker than those of the other two parts. It extends from 

 the pylorus, which lies in the transpyloric plane half an inch 

 to the right of the median plane, to the duodenal flexure, 

 situated at the left side of the second lumbar vertebra slightly 

 below the transpyloric plane and about an inch to the left of 

 the median plane. Whilst passing from its commencement 

 to its termination the duodenum describes a U-shaped curve, 

 the concavity of the curve, which embraces the head of the 

 pancreas, being directed upwards and to the left. For con- 



