On both left and right sides at the venous end of the developing heart, the omphalomesenteric vein and the umbilical vein come together to form the sinual horns. The omphalomesenteric vein is located medially, the umbilical vein laterally. At S11, the common cardinal vein joins the venous end laterally. The sinual horns merge to form a common sinus venosus. These alignments result in blood flowing in sequence through the following parts: the right and the left atrium, the atrio-ventricular canal (AV canal), the left and the right ventricle, and finally the outflow tract (conus cordis and truncus arteriosus). At the arterial end, the heart connects to the first paired aortic arches through the aortic sac.