(A) Primitive umbilical cord with midgut herniation, umbilical vein (in blue), umbilical artery (in red), and the urachus (in yellow). (B) When the urachus remains patent, an allantoic cyst (ac) develops in the center of the umbilical vessels. (C) The expanding allantoic cyst (ac) will push the vessels to the periphery.
