666 THE VASCULAR SYSTEMS 



The inferior mesenteric artery (a. mesenterica inferior} (Figs. 467 and 472) 

 supplies the descending colon, the sigmoid flexure of the colon, and the greater 

 part of the rectum. It is smaller than the superior mesenteric, and arises from 

 the front and toward the left side of the aorta, between one and two inches above 

 the division of that vessel into the common iliacs. It passes downward 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 as the superior hemor- 

 rhoidal in front of the left common iliac artery. 



Fir.. 471. The superior mesenteric artery and its branches. 



Dissection. In order to expose the inferior mesenteric artery 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 of the aorta. 



Branches. Its branches are: 



Left colic. Sigmoid. 



Superior hemorrhoidal. 



The left colic artery (a. colica sinistra) passes behind the peritoneum, in front 

 of the left kidney, to reach the descending colon; it divides into an ascending 



