The umbilical cord is covered by simple squamous amniotic epithelium. It contains the ______1_____, __2__, _____3_____ and __4__. The two arteries are spirally twisted around each other. The right __5__ later completely disappears. The __4__ remains open until just before birth but the __2__ closes at about day 70. The umbilical cord can be as long as _6_ cm and is, relatively, the longest of all domestic mammals.