INFERIOR MESENTERIC. 425 



The ileo-colic artery is the lowest branch given off from the concavity of the 

 superior mesenteric artery. It descends between the layers of the mesentery to 

 the right iliac fossa, where it divides into two branches. Of these the inferior 

 one inosculates with the lowest branches of the vasa intestini tenuis, from the 

 convexity of which branches proceed to supply the termination of the ileum, the 

 ccecum and appendix coeci, and the ileo-ccecal and ileo-colic valves. The superior 

 division inosculates with the colica dextra, and supplies the commencement of 

 the colon. 



The colica dextra arises from about the middle of the concavity of the superior 

 mesenteric artery, and, passing beneath the peritoneum to the middle of the ascend- 

 ing colon, divides into two branches ; a descending branch, which inosculates with 

 the ileo-colic, and an ascending branch which anastomoses with the colica media. 

 These branches form arches, from the convexity of which vessels are distributed 

 to the ascending colon. The branches of this vessel are covered with peritoneum 

 only on their anterior aspect. 



The colica media arises from the upper part of the concavity of the superior 

 mesenteric, and, passing forwards between the layers of the transverse mesocolon, 

 divides into two branches ; the one on the right side inosculating with the colica 

 dextra, that on the left side with the colica sinistra, a branch of the inferior 

 mesenteric. From the arches formed by their inosculation, branches are dis- 

 tributed to the transverse colon. The branches of this vessel lie between two 

 layers of peritoneum. 



INFERIOR MESENTERIC ARTERY. 



In order to expose this vessel, draw the small intestines and mesentery over to the right side 

 of the abdomen, raise the transverse colon towards the thorax, and divide the peritoneum cover- 

 ing the left side of the aorta. 



The Inferior Mesenteric Artery (fig. 226) supplies the descending and sig- 

 moid flexure of the colon, and greater part of the rectum. It is smaller than the 

 superior mesenteric, and arises from the left side of the aorta, between one and 

 two inches above its division into the common iliacs. It passes downwards to the 

 left iliac fossa, and then descends, between the layers of the mesorectum, into the 

 pelvis, under the name of the superior hemorrhoidal artery. It lies at first in close 

 relation with the left side of the aorta, and then passes in front of the left common 

 iliac artery. Its branches are the 



Colica sinistra. Sigmoid. 



Superior hemorrhoidal. 



The colica sinistra passes behind the peritoneum, in front of the left kidney, 

 to reach the descending colon, and divides into two branches ; an ascending branch, 

 which inosculates with the colica media, and a descending branch, which anasto- 

 moses with the sigmoid artery. From the arches formed by these inosculations, 

 branches are distributed to the descending colon. 



The sigmoid artery runs obliquely downwards across the Psoas muscle to the 

 sigmoid flexure of the colon, and divides into branches which supply that part of 

 the intestine ; anastomosing above, with the colica sinistra, and, below, with the 

 superior hemorrhoidal artery. This vessel is sometimes replaced by three or four 

 small branches. 



The superior hemorrhoidal artery, the continuation of the inferior mesen- 

 teric, descends into the pelvis between the layers of the mesorectum, crossing, in 

 its course, the ureter, and left common iliac vessels. Opposite the middle 

 of the sacrum it divides into two branches, which descend one on each side of the 

 rectum, where they divide into several small branches, which are distributed 

 between the mucous and muscular coats of that tube, to near its lower end ; anas- 

 tomosing with each other, with the middle hemorrhoidal arteries, branches of the 

 internal iliac, and with the inferior hemorrhoidal, branches of the internal pudic. 



The student should especially remark, that the trunk of the vessel descends 



