THE DUODENUM 255 



crosses in front of the inferior vena cava and the abdominal 

 aorta, and it is itself crossed anteriorly by the superior 

 mesenteric vessels and the root of the mesentery. 



With the patient in the dorsal decubitus the duodenum 

 may be mapped out on the surface with a tolerable amount 

 of accuracy, for, since for the most part it is retro-peritoneal, 

 its position undergoes little variation. From the pylorus 

 (p. 243), the first part passes upwards and to the right for 

 a distance of from ij to 2 inches. The second part descends 

 medial to the right lateral plane to the level of the umbilicus. 

 The third part passes to the left, below and parallel to the 

 subcostal plane (p, 233), and, on the left side of the median 

 plane, it ascends to the duodeno-jejunal flexure. The latter 

 point lies i inch below the transpyloric plane (p. 234) and 

 about i inch to the left of the median plane (Fig. 124). 



The nerves which supply the duodenum are carried on the 

 walls of its arteries. These are derived from two sources, namely, 

 the cceliac artery and the superior mesenteric, and the nerves 

 which they convey belong partly to the group of sympathetic 

 nerves which supplies the stomach and partly to the group 

 which supplies the jejunum. The centres for these nerves in 

 the spinal medulla lie in the lower thoracic region (T. 8 and 9) 

 and overlap the centres for the stomach and the jejunum. 

 On this account the referred pain which is experienced in 

 duodenal ulcer cannot be distinguished from the referred pain 

 caused by a gastric ulcer in the pyloric region, and the pain 

 initiated by violent peristaltic movements of the duodenum in 

 chronic intestinal stasis (p. 257) is in every way similar to the 

 pain experienced in violent peristalsis of the jejunum. 



Some of the terminal branches of the vagi assist the 

 sympathetic nerves to supply the duodenum. 



The Jejunum and Ileum constitute the freely movable 

 part of the small intestine, and they are attached to the 

 posterior abdominal wall by a continuous dorsal mesentery, 

 which begins above on the left side of the second lumbar 

 vertebra and, extending downwards and to the right, ends 



