Umbilical artery

In the fetus, the internal iliac artery is twice as large as the external iliac, and is the direct continuation of the common iliac artery. It ascends along the side of the bladder, and runs upward on the back of the anterior wall of the abdomen to the umbilicus, converging toward its fellow of the opposite side. Having passed through the umbilical opening, the two arteries, now termed umbilical arteries, enter the umbilical cord, where they are coiled around the umbilical vein, and ultimately ramify in the placenta.

At birth, when the placental circulation ceases, the pelvic portion only of the artery remains patent (patent part of umbilical artery) and constitutes the internal iliac artery and the first part of the superior vesical artery of the adult; the remainder of the vessel is converted into a solid fibrous cord, the medial umbilical ligament (Occluded part of umbilical artery - Pars occlusa arteriae umbilicalis) which extends from the pelvis to the umbilicus.