When the allantois develops its arteries are in fact end-branches of the two primitive aortae. After their fusion and after the formation of the single aorta this vessel is continued beyond the umbilical arteries as a small trunk, the caudal artery or rudiment of the adult sacralis media. Consequently the umbilical arteries are really lateral branches of a median vessel, viz., aorta abdominalis and arteria sacralis media. But as the umbilical vessels are very large and the caudal aorta very small, the former, even under these conditions, appear as the real terminal branches of the abdominal aorta. The arteries supplying the yolk-sac and subsequently the intestinal canal are the vitelline or omphalo-mesenteric. At first they are branches derived from the two primitive aortae, and after the fusion of these vessels they arise from the resulting single abdominal aorta. The omphalo-mesenteric arteries are at first multiple and later are reduced to two. When the primitive intestine loses its original close contact with the vertebral column and the common dorsal mesentery develops, the two omphalo-mesenteric arteries unite to form a single vessel, running between the layers of the mesentery. After a short course this artery divides again into two branches, passing one on each side, around the intestinal tube, which has in the meanwhile become closed. Ventrad of the intestine these branches reunite so that the gut is surrounded by a vascular circle. The left half of this loop becomes obliterated and the trunk of the omphalo-mesenteric artery now passes on the right side of the intestine to the umbilicus. The peripheral segment of the omphalo-mesenteric artery disappears with the cessation of the vitelline circulation. The proximal portion, situated between the layers of the mesentery, gives numerous anastomosing branches to the intestine and is converted into the main trunk of the superior mesenteric artery. The derivation of the superior mesenteric as the fully developed proximal segment of the embryonic omphalo-mesenteric artery passing to the yolk-sac is responsible for the rare anomaly in the adult of a branch of the superior mesenteric artery continuing beyond the intestine to the umbilicus. I have encountered one instance of this persistence of the intra-abdominal portion of the omphalo-mesenteric artery in a male subject 54 years of age. A connective strand, containing a small artery derived from the superior mesenteric vessels, extended between the right layer of the mesentery, some distance from its attached border, and the ventral abdominal wall at the umbilicus. The vessel which was pervious throughout, was the size of one of the digital arteries.