A continuous anastomotic channel along the mesenteric border of the colon
Expansion
The marginal artery of Drummond runs along the mesenteric border of the colon, from the ileocaecal junction to the rectosigmoid, formed by anastomosing branches of the ileocolic, right colic, middle colic, left colic and sigmoid arteries. Short vasa recta pass from it to the bowel wall.
A second, more central and variable collateral, the arc of Riolan (meandering mesenteric artery), connects the middle colic and left colic arteries closer to the aorta. A prominent arc on imaging is a clue to significant proximal stenosis.
Together these allow the colon to survive ligation of a major mesenteric trunk, which is what makes colonic resection feasible.
The collateral is weakest at the splenic flexure and at the rectosigmoid junction, so these are the sites of ischaemic colitis.