Normal Anatomy Umbilical arteries right and left umbilical arteries branching from internal iliac arteries return deoxygenated blood from the fetus single umbilical artery is associated with increased likelihood of congenital abnormalities Umbilical vein single umbilical vein returns oxygenated blood from placenta to fetus Allantois forms the umbilical arteries and vein Abnormalities Urachal duct a duct extending from yolk sac to apex of the bladder yolk sac forms allantois which becomes urachus during development, the lumen of the uraches closes adult remnant is median umbilical ligament if urachus fails to close patent urachus urine leaks from umbilicus vesicourachal diverticulum bladder protrudes from umbilicus Vitelline duct (omphalomesenteric duct) connects yolk sac to midgut, closes during week 7 if vitelline duct lumen fails to close then vitelline fistula meconium discharge from umbilicus Meckel's diverticulum (see "Meckel's Diverticulitis") failure of lumen to close on side opening to ileum can have ectopic gastric mucosa leading to melena and RLQ pain