324 ABDOMEN 



in front of the lower part of the left kidney, to the trans 

 verse meso-colon, where it inosculates with the middle colic 

 artery. The other descends, behind the peritoneum of the 

 posterior wall of the abdomen, to unite with the superior 

 sigmoid artery. From the arches thus formed twigs are 

 supplied to the transverse colon, the left flexure of the colon, 

 and the descending colon. The point of division into upper 

 and lower branches is very variable. 



Arterise Sigmoidese. The sigmoid arteries, one to three 

 in number, are distributed to the lower part of the descending 

 colon, the iliac colon, and the pelvic colon. The highest 

 branch enters the left iliac fossa, behind the parietal peri- 

 toneum. It sends a branch upwards to form an arch with 

 the descending branch of the left colic, and another down- 

 wards, which ultimately enters the pelvic meso-colon and 

 joins the other sigmoid branches. The lower sigmoid 

 arteries pass into the pelvic meso-colon, and there form a 

 series of arcades, varying in number according to the length 

 of that mesentery; from those arcades the twigs for the 

 supply of the pelvic colon are given off. 



The superior hczmorrhoidal artery will be followed out in 

 the dissection of the pelvis minor. 



Vena Mesenterica Inferior. The inferior mesenteric vein 

 receives- tributaries corresponding with the branches of the 

 inferior mesenteric artery. It passes upwards, upon the psoas 

 major muscle, under cover of the peritoneum, to the left of, 

 and at some distance from, the artery, and, after disappear- 

 ing behind the pancreas, it ends in the splenic vein. 



Plexus Mesentericus Inferior. The inferior mesenteric 

 plexus of nerve fibres is an offshoot from the left side of the 

 aortic plexus. It closely surrounds the artery, and sends twigs 

 along the branches of the vessel to supply the left half of 

 the large intestine. 



Plexus Aorticus Abdominalis. The abdominal aortic 

 nerve plexus is placed upon the aorta, between the origins 

 of the two mesenteric arteries. It is more strongly marked 

 upon the sides of the artery than in front of it. Its con- 

 tinuity, above, with the cceliac and renal plexuses, will be 

 demonstrated at a later stage of the dissection. From its 

 lower extremity several large branches descend, in front of 

 the common iliac arteries, to join the hypogastric plexus 

 a plexus which is situated in front of the fifth lumbar 



