Mesenteric artery that supplies the large intestine from the left colic (or splenic) flexure to the upper part of the rectum, which includes the descending colon, the sigmoid colon, and part of the rectum. Proximally, its territory of distribution overlaps (forms a watershed) with the middle colic artery, and therefore the superior mesenteric artery. The SMA and IMA anastomose via the marginal artery (artery of Drummond). The territory of distribution of the IMA is more or less equivalent to the embryonic hindgut. [WP,unvetted].