318 



DISSECTION OF THE ABDOMEN. 



Sigmoid 

 branch 

 tosigmoid 

 flexure. 



Branch to 

 rectum. 



Inferior 

 mesenteric 

 vein : 



origin, 

 course, and 



termination. 



No valves 

 in veins. 



Lymphatic 

 glands . 



Plexuses of 

 the sympa- 

 thetic to the 



Dissection 

 of 



aortic 

 plexus, and 



hypogastric 

 plexus. 



Superior 



mesenteric 



plexus 



is on artery 

 of same 

 name: 



secondary 

 plexuses. 



supply of the descending colon : by the ascending offset it anasto- 

 moses with the middle colic branch of the superior mesenteric. 



b. The sigmoid artery (or commonly arteries) (d) is distributed to 

 the iliac and pelvic colon (sigmoid flexure), and divides into offsets 

 which anastomose above with the preceding colic, and below with the 

 ha3inorrhoidal branch. Here, as in the rest of the intestinal tube, 

 arches are formed by the arteries before they reach the intestine. 



c. The superior hcemorrhoidal artery (e) crosses over the left 

 common iliac vessels, and enters between the layers of the pelvic 

 meso-colon, to be distributed to the lower end of the large intestine, 

 its branches reaching in the mucous membrane of the rectum as far 

 as the anus : it will be described in the dissection of the pelvis. 



The inferior mesenteric vein (tig. 125, d, p. 334) begins in the part of 

 the large intestine to which its companion artery is distributed, and 

 ascends over the psoas muscle higher than the origin of the artery. 

 Passing beneath the pancreas, the vein inclines to the right, and 

 opens into the superior mesenteric trunk at its junction with the 

 splenic, or sometimes into the splenic vein. 



Both mesenteric veins are without valves, and may be injected 

 from the trunk to the branches, like an artery. 



Lymphatic glands are ranged along the descending colon and the 

 sigmoid flexure. The absorbents of the intestine, after passing 

 through these glands, enter the left lumbar lymphatic glands. 



SYMPATHETIC NERVE. The following plexuses of the sympathetic 

 on the vessels, viz., superior mesenteric, aortic, spermatic, and in- 

 ferior mesenteric, are derived from the solar plexus beneath the 

 stomach, and can now be exposed. The remaining portion of the 

 sympathetic nerve in the abdomen will be subsequently referred 

 to (pp. 336 et seq.). 



Dissection* On the two mesenteric arteries the dissector will have 

 already made out the plexuses of nerves distributed to the intes- 

 tinal tube beyond the duodenum. 



He has now to trace on the aorta the connecting nerves between 

 the mesenteric plexuses, by taking away the peritoneum from the 

 front of the aorta below the pancreas. From the upper part of the 

 aortic plexus an offset is to be followed along the spermatic artery ; this 

 may be done on the left side, where that vessel is partly laid bare. 



By detaching the peritoneum below the bifurcation of the aorta, 

 and following downwards over the iliac arteries the nerves from the 

 aortic plexus and the lumbar ganglia, the dissector will arrive at the 

 hypogastric plexus, above the promontory of the sacrum. 



The superior mesenteric plexus is a large bundle of nerves, and is 

 distributed to the same extent of the intestinal tube as the mesenteric 

 artery. The nerves surround closely the trunk and larger branches 

 of the artery ; but near tlu intestine some of them leave the vessels, 

 and divide and communicate before entering the gut. The offsets 

 of the main plexus are named after the arteries which they accom- 

 pany, viz., intestinal nerves to the small intestine, and ileo-colic, 

 right colic, and middle colic plexuses to the large intestine. 



