In the embryo, a pair of veins bringing oxygenated blood to the developing heart from the placenta. During development, the right umbilical vein disappears. The left umbilical vein then carries all the oxygenated blood from the placenta via the umbilical cord to the fetus. As the embryonic liver develops, the umbilical vein persists alongside it as a bypass (the ductus venosus) for blood going directly into the inferior vena cava. After birth, the umbilical vein closes and becomes a fibrotic cord, the ligamentum teres, running in the falciform ligament along the ventral wall of the abdomen from the umbilicus to the liver. The ductus venosus also closes and remains as the ligamentum venosum of the liver.