The superior mesenteric and inferior mesenteric arteries communicate with each other via several anastomoses. One of them is formed between the middle colic artery and the left colic artery. However, it can also be created directly between the proximal superior mesenteric artery and the proximal inferior mesenteric artery. It is an inconstant anastomosis called the arc of Riolan or the central anastomotic mesenteric artery (also, the intercolic anastomotic artery).