The vitelline duct and the communication between endo- and exocoelom close early; the ____ ____, however, persists as a thin-walled passage, which remains open until birth. The cord's intervening mucous connective tissue (____ ____) soon becomes fibrous. A funnel-shaped extension of hairy skin from the abdominal wall of the fetus is seen to cover a short portion of the umbilical cord before it abruptly goes over into the smooth, thin-walled _____.