THE ABDOMINAL AORTA 



667 



branch which anastomoses with the middle_colic, and a descending branch which 

 anastomoses with the upper sigmoid artery. From the arches formed by these 

 anastomoses, branches are distributed tc the descending colon. 



The sigmoid arteries (aa. sigmoideae) run obliquely downward and outward 

 behind the peritoneum across the Psoas muscle to the sigmoid flexure of the colon. 

 They divide into branches which supply the lower part of the descending colon and 

 the sigmoid flexure, anastomosing above with the left colic, and below with the 

 superior hemorrhoidal artery. 



Middle hemorrhoidal 

 Inferior hemorrhoidal. 



FIG. 472. The inferior mesenteric and its branches. 



The superior hemorrhoidal artery (a. haemorrhoidalis superior) (Figs. 472 and 

 473), the continuation of the inferior mesenteric, descends into the pelvis between 

 the layers of the mesorectum, crossing, in its course, the left ureter and left common 

 iliac vessels. Opposite the middle of the sacrum it divides into two branches, 

 which descend one on either side of the rectum, and about five inches from t-he 

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

 bowel and run downward, as straight vessels, placed at regular intervals from 

 each other in the wall of the intestine between its muscular and mucous coat, to the 

 level of the Internal sphincter; here they form a series of loops around the lower 

 end of the rectum, and communicate with the middle hemorrhoidal arteries, which 

 are branches of the internal iliac, and with the inferior hemorrhoidal branches of 

 the internal pudic. 



