A novel branching pattern of the superior mesenteric artery found in the bullfrog (Rana catesbeiana) amphibian.

The branching and distribution patterns of the superior mesenteric artery were studied in 10 adult bullfrogs (Rana catesbeiana) after injection of coloured latex solution into the vasculature. The abdominal digestive organs in the bullfrog were mainly supplied by the coeliac artery and the superior mesenteric artery, both of which arose as a common trunk, the coeliacomesenteric artery, from the abdominal aorta. The coeliac artery supplied the stomach, liver, gallbladder and the pancreas, whereas the first branch of the superior mesenteric artery was the splenic artery with other branches supplying the greater part of intestine. The apex of the intestinal loop was defined as the region supplied by the trunk of the superior mesenteric artery, and its intestinal branches constituted a 'nested formation' which had the following characteristics. (1) The branches of the trunk were distributed to both sides of the apex, and the distribution regions of younger branches were located more distant from the apex than those of older branches. (2) Two branches directed towards both sides of the trunk frequently made a common stem arising from the trunk. The second branch of the superior mesenteric artery constituted a secondary trunk and its distribution region could be defined as a secondary apex, since 1 of its branches also constituted a nested formation which was distributed to both sides of the primary and secondary apices. The intestinal branches of the superior mesenteric artery were divided into 4 types on the basis of their pattern of branching and course. It is suggested that the nested formation of the superior mesenteric artery in the bullfrog is a remnant of the vascular pattern of the tadpole, which possesses a double spiral mode of intestinal convolution, probably supplied by arteries with the nested formation in a latent form.