340 ABDOMEN 



considered in association with the dissection of the pelvis 

 minor. 



Dissection. Place two ligatures round the descending colon, 

 below the left colic flexure, and two more ligatures round the 

 junction of the iliac with the pelvic colon ; divide the bowel 

 between each pair of ligatures and remove the descending and the 

 iliac portions of the colon. Take the detached bowel 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 yilli and of plicae circulares. After the separated 

 parts of the intestine have been examined, clean the posterior 

 wall of the abdomen in the regions from which they were removed 

 and thus expose the structures which form their posterior rela- 

 tions. The structures behind the descending colon are the 

 same as those behind the ascending colon (see p. 333), with the 

 exception of the iliacus muscle, because the descending colon 

 ends at the level of the crest of the ilium. Behind the iliac colon 

 are the left iliacus muscle ; the lateral cutaneous nerve of the thigh 

 in front of the iliacus muscle ; the left psoas major muscle ; the 

 femoral nerve in the angle between the iliacus and the psoas 

 major ; the spermatic vessels and the genito-femoral nerve in 

 front of the psoas major ; and the external iliac vessels at the 

 inlet of the pelvis minor. After the structures mentioned 

 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. 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 examina- 

 tion of the stomach, had it not been that a complete examina- 

 tion 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 25 to 30 cm. (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 duodeno-jejunal flexure, which is 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 termina- 

 tion the duodenum describes a C-shaped curve, the concavity 

 of the curve, which embraces the head of the pancreas, being 

 directed upwards and to the left (Fig. 156). 



For convenience of description the duodenum is divided into 

 three parts (i) superior, (2) descending, (3) inferior, and the 



