430 AETERIES OF THE ABDOMEN. 



1. The ilco-colic artery, the first in order from below upwards, inclines 

 downwards and to the right side, towards the ileo-colic valve, near which 

 it divides into two branches : one of these descends to inosculate with 

 the termination of the mesenteric artery itself, and to form an arch, 

 from the convexity of which branches proceed to supply the junction of 

 the small with the large intestine, and the ca3cum and its appendix ; 

 the other division ascends and inosculates with the next mentioned 

 branch. The ileo-colic artery is not always distinct from the termina- 

 tion of the superior mesenteric. 



2. The right colic artery passes transversely towards the right side, 

 beneath the peritoneum, to the middle of the ascending colon, opposite 

 to which it divides into two branches, of which one descends to com- 

 municate with the ileo-colic artery, whilst the other ascends to join in 

 an arch with the middle colic. This artery and the ileo-colic often 

 arise by a common trunk. 



3. The miildJe colic artery passes upwards between the layers of the 

 mesocolon towards the transverse colon, and divides in a manner 

 exactly similar to that of the vessels just noticed. One of its branches 

 inclines to the right, where it inosculates with the preceding vessel ; 

 the other descends to the left side, and maintains a similar communica- 

 tion with the left colic branch, derived from the inferior mesenteric 

 artery. From the arches of inosculation thus formed, small branches 

 pass to the colon for the supply of its coats. 



Those branches of the superior mesenteric artery which supply the 

 ascending colon have a layer of peritoneum only on their anterior 

 aspect : the others lie between two strata. 



Varieties. — The number of the branches of this artery, both intestinal and 

 celic. is by no means constant. It also frequently gives off accessory branches to 

 the neighbouring viscera : of these that to the liver is the most common. It 

 may rc]ilace the gastro-duodenal or its chief branch, the right epiploic (Henle), 

 or it may give accessory pancreatic and splenic branches (Hj-iil). It has also 

 been seen to give off the left colic and superior ha^morrhoidal arteries when the 

 inferior mesenteric was absent (Fleischmann). A rare anomaly is the presence 

 of an omphalo-mesenteric artery, arising either from the main stem or from one 

 of the branches of the superior mesenteric. In one case it ran direct to the 

 umbilicus where it gave a branch to the urachus (Hallcr). In another it reached 

 the anterior waU of the abdomen rather below the umbilicus, and after giving 

 a branch to the rectus, which anastomosed with the deep eiiigastric, it ter- 

 minated by winding round the ligamentum teres, and forming a capillary net- 

 work on the suspensory ligament of the liver (Hji-tl). 



Inferior mesenteric artery. — This artery, mu-ch 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 one 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 

 JiccmorrhoicM 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. 



BRAi<rcHES. — (a) The i^ft colic a^-tery is directed to the left side 

 behind the peritoneum, and across the left kidney to reach the descend- 



