3i8 ABDOMEN 



left ureter, which passes downwards, behind the internal sper- 

 matic vessels and the left colic and sigmoid arteries, to the 

 lower end of the left common iliac artery. Running down- 

 wards and laterally behind the left ureter, on the front of the 

 left psoas major muscle, is the left genito-femoral nerve, and 

 beyond the lateral border of the left psoas is the fascia on the 

 front of the medial part of the left quadratus lumborum. Along 

 the anterior border of the psoas, at the left of the aorta, is the 

 left sympathetic trunk. The right sympathetic trunk is con- 

 cealed by the inferior vena cava. 



When the dissector has found and defined all the structures 

 mentioned, he should commence the study of the superior and 

 the inferior mesenteric arteries and their branches. He will 

 find that the superior mesenteric supplies the terminal portions 

 of the duodenum, the whole of the jejunum and the ileum, the 

 caecum, the ascending colon and the greater part of the trans- 

 verse colon ; that the inferior mesenteric supplies the left part 

 of the transverse colon, the left flexure of the colon, the descend- 

 ing colon, the iliac colon, and the pelvic colon, and that it 

 furnishes also the greater part of the blood supply of the rectum, 

 by means of its continuation the superior hasmorrhoidal 

 artery. He will find also that there is a very free anastomosis 

 between the left colic branch of the inferior mesenteric artery 

 and the middle colic branch of the superior mesenteric artery. 

 At a later period he will find that an inferior pancreatico-duo- 

 denal branch of the superior mesenteric artery anastomoses with 

 the superior pancreatico-duodenal branch of the gastro-duodenal 

 artery, and when he recalls to mind the fact that the gastro- 

 duodenal artery is a branch of the hepatic, and that it furnishes 

 the right gastro-epiploic, which passes to the stomach and 

 anastomoses on its surfaces with the other arteries which supply 

 that viscus, he will recognise that a complete chain of arterial 

 anastomoses runs along the wall of the abdominal part of the 

 alimentary canal, providing for the continuance of the blood 

 supply to the wall of the gut in the event of one or more of the 

 bigger trunks being temporarily or permanently occluded. 



Arteria Mesenterica Superior. The superior mesenteric 

 artery springs from the front of the abdominal aorta about 

 6.5 mm. (quarter of an inch) below the coeliac artery. At its 

 origin it is covered by the neck of the pancreas, and it is 

 crossed by the splenic vein. After it emerges from under 

 cover of the neck of the pancreas, it proceeds downwards, 

 in front of the lower portion of the head of the pancreas ; then 

 it crosses the inferior part of the duodenum, to the right of the 

 duodeno-jejunal flexure, and enters the root of the mesentery 

 proper, along which it proceeds to the right iliac fossa, where 

 it ends by anastomosing with one of its own branches. 

 Between its extremities it is slightly curved, the convexity of 

 the curve being directed to the left. It is accompanied by 

 the superior mesenteric vein, which lies upon its right side, 



