412 ABDOMINAL AORTA. 



ing colon have a layer of peritoneum only on their anterior aspect : the 

 others lie between two strata. 



The superior mesenteric artery is occasionally connected at its origin with the 

 cceliac artery. Not unfrequently it furnishes the hepatic artery. 



III. INFERIOR MESENTERIC ARTERY. 



This artery, much smaller than the superior mesenteric, supplies the lower 

 half of the colon, and the greater part of the rectum. It arises from the 

 aorta, between an inch and two inches above the bifurcation of that trunk. 



The inferior mesenteric artery inclines to the left side in the direction of 

 the left iliac fossa, from which point it descends between the layers of the 

 mesorectum into the pelvis, and, under the name of " superior hsernor- 

 rhoidal " artery, runs down behind the rectum. It lies at first close to the 

 aorta, on its left side, and then crosses over the left common iliac artery. 



BRANCHES. (a). The left colic artery is directed to the left side behind 

 the peritoneum, and across the left kidney to reach the descending colon. 

 Jt divides into two branches, and forms a series of arches in the same way 

 as the colic vessels of the opposite side. One of these two branches passes 

 upwards along the colon, and inosculates with the descending branch of 

 the middle colic ; whilst the other descends towards the sigmoid flexure, 

 and anastomoses with the sigmoid artery. 



(6) The sigmoid artery runs obliquely downwards to the sigmoid flexure 

 of the colon, where it divides into branches ; some of which incline upwards 

 and form arches with the preceding vessel, while others turn downwards to 

 the rectum and anastomose with the following branch. Instead of a single 

 sigmoid artery, two or three branches are sometimes present. 



(c) The superior hcemorrhoidal artery, the continuation of the inferior 

 mesenteric, passes^ into the pelvis behind the rectum, at first in the meso- 

 rectum, and then divides into two branches which extend one on each side 

 of the intestine towards the lower end. About five inches from the anus 

 these subdivide into branches, about a line in diameter, which pierce the 

 muscular coat two inches lower down, in the intestine, these arteries, about 

 seven in number, and placed at regular distances from each other, descend 

 between the mucous and muscular coats to the end of the gut, where they 

 communicate in loops opposite the internal sphincter, and end below by 

 anastomosing with the middle and inferior haemorrhoidal arteries. 



ANASTOMOSES ON THE INTESTINAL TUBE. The arteries distributed to the 

 alimentary canal communicate freely with each other over the whole length 

 of that tube. The arteries of the great intestine derived from the two 

 mesenteric arteries, form a range of vascular arches along the colon and 

 rectum, at the lower end of which they anastomose with the middle and 

 inferior hsemorrhoidal arteries, given from the internal iliac and pudic 

 arteries. The branches from the left side of the superior mesenteric form 

 another series of arches along the small intestine, which is connected with 

 the former by the ileo-colic artery. Farther, a branch of the superior 

 mesenteric joins upon the duodenum with the pancreatico-duodenal artery. 

 The latter, at its commencement, is in a manner continuous with the pyloric 

 artery ; and so likewise, through the coronary artery of the stomach and 

 its ascending branches, a similar connection is formed with the cesophageal 

 arteries, even up to the pharynx. 



