We have encountered in our anatomical practice the first case and an extremely rare second case in which the ascending, transverse, descending, and sigmoid colons were supplied by the inferior mesenteric artery. The causes of colic artery anomalies are generally explained in conjunction with the development of the superior mesenteric artery, which is intimately related to embryonic elongation and midgut rotation. However, this embryological model was inapplicable to both cases. This difficulty motivated us to seek possible relationships with reported anomalous inferior mesenteric arteries in adults as well as their embryological causes. We consider that the aberrant right colic artery found in 2009 is an "intermesenteric artery" which anastomoses the superior (or its middle colic branch) and inferior mesenteric artery, but secondarily lost its origin from the superior mesenteric artery. The aberrant colic artery found in 2010 is a "middle-inferior mesenteric artery" in which the inferior mesenteric artery formed a common trunk with remnant middle mesenteric artery.