Fig. 3.

Vascular pattern in a normal versus sirenomelia fetus. (A) Schematic drawing of the fetal umbilical cord vasculature in a normal and a sirenomelia fetus. Note the abnormally high origin of the SUA in sirenomelia and the hypoplasia of the aorta caudal to its origin. (B) Left two panels: schematic of transverse sections at the caudal level of an early normal and sirenomelia embryo. Below each section, the corresponding vascular pattern is shown in red. Ao, dorsal aorta; rpAo, recurved distal portions of aorta; UA, umbilical arteries; UV, umbilical vein; SUA, single umbilical artery; VA, vitelline artery. Right panel: a schematic lateral view of an embryo in which the great caudal vessels are shown in red and the hindgut in yellow. The broken red line indicates the level of the sections shown in the two panels to the left.