Which of the following is not a constituent of umbilical cord:

The constituents of the umbilical cord when fully developed are covering epithelium, whaon's jelly, blood vessels, remnant of the umbilical vesicle (yolk sac) and its vitelline duct, allantois and obliterated extraembryonic coelom Umbilical cord: The umbilical cord develops from and contains remnants of the yolk sac and allantois. It forms by the fifth week of fetal development, replacing the yolk sac as the source of nutrients for the fetus. The length of the umbilical cord is approximately equal to the crown-rump length of the fetus throughout pregnancy. The umbilical cord in a full term neonate is usually about 50 centimeters (20 in) long and about 2 centimeters (0.75 in) in diameter. The blood flow through the umbilical cord is approximately 35 ml / min at 20 weeks, and 240 ml / min at 40 weeks of gestation. Adapted to the weight of the fetus, this corresponds to 115 ml / min / kg at 20 weeks and 64 ml / min / kg at 40 weeks. Cloacal duct It is a small communication between the 2 poions of the hindgut. Down growth of the urorectal septum is believed to close this duct by 7 weeks' gestation.