AMONG THE RARER CONDITIONS which are encountered in surgery those which precipitate practical problems are especially worthy of consideration. Persistent omphalomesenteric, or vitelline, artery falls into this category. Its presence is one of the infrequent causes of intestinal obstruction. The literature contains only i6 cases in which a persistent omphalomesenteric artery caused symptoms, and, of this number, evidence of intestinal obstruction was found at operation or autopsy in ii cases (69 per cent). In addition, six asymptomatic cases have been reported, making a total of 22 cases of persistent omphalomesenteric artery in the literature.Of these 22 cases, a Meckel's diverticulum of the ileum was present in I3(59 per cent). Of the ii cases presenting evidence of intestinal obstruction at operation or autopsy, IO (9I per cent) had a coexistent Meckel's diverticulum. This association is not surprising if we consider the origins and fates of these structures in the embryo.EMBRYOLOGY 1,2,4,13,18,26,26 The yolk sac is demonstrable at the second week of intra-uterine life. The yolk sac and the primitive gut are connected to each other by the yolk-stalk, or vitelline (omphalomesenteric) duct. The part of the gut to which the omphalomesenteric duct is attached is the midgut; from it are derived the small intestine (except the first part of the duodenum), the cecum, the ascending colon and the transverse colon.During the first weeks of embryonal development, the aorta is a paired structure (Fig. i). From each portion a prominent vessel courses ventrally to the primitive gut and thence out along the yolk-stalk to reach the yolk sac. With the merging of the paired aorta into a single aorta the two main ventral branches merge and the resultant vessel comes to be the superior mesenteric artery (Figs. 2 and 3

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