THE INFERIOR MESENTERIC ARTERY. 555 



intestine. From the terminal arches numerous small straight vessels arise which 

 encircle the intestine, upon which they are distributed, ramifying between its 

 coats. Throughout their course small branches are given off to the glands and 

 other structures between the layers of the mesentery. 



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 

 division inosculates with the termination of the superior mesenteric artery, forming 

 with it an arch, from the convexity of which branches proceed to supply the termi- 

 nation of the ileum, the csecum and appendix cseci, and the ileo-caecal valve. The 

 superior division inosculates with the colica dextra and supplies the commence- 

 ment of the colon. 



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

 mesenteric artery, and, passing behind the peritoneum to the middle of the 

 ascending colon, divides into two branches a descending branch, which inoscu- 

 lates with the ileo-colic ; and the 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 forward between the layers of the transverse meso-colon, 

 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 distrib- 

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

 of the transverse meso-colon. 



The Inferior Mesenteric Artery (Fig. 311). 



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

 side of the abdomen, raise the transverse colon toward the thorax, and divide the peritoneum 

 covering the front side of the aorta. 



The Inferior Mesenteric Artery supplies the descending and sigmoid flexure of 

 the colon and the 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 downward to the left 

 iliac fossa, and then descends, between the layers of the meso-rectum, into the 

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

 relation with the left side of the aorta, and then passes as the superior haemor- 

 rhoidal in front of the left common iliac artery. Its branches are the 



Colica Sinistra. Sigmoid. 



Superior Haemorrhoidal. 



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 

 anastomoses with the sigmoid artery. From the arches formed by these inoscu- 

 lations branches are distributed to the descending colon. 



The sigmoid artery runs obliquely downward 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 haeinorrhoidal artery. This vessel is sometimes replaced by three or four 

 small branches. 



The superior haemorrhoidal artery, the continuation of the inferior mesenteric, 

 descends into the pelvis between the layers of the meso-rectum, crossing, in its 

 course, the ureter and left common iliac vessels. It divides into two branches, 

 which descend one on each side of the rectum, and about five inches from the anus 

 break up into several small branches, which pierce the muscular coat of the bowel 



