The placenta (Greek, plakuos = flat cake) named on the basis of this organs appearance. This  is the connecting region between the functional placenta and the embryo/fetal umbilical region. The human cord varies greatly in overall length increasing to about 60 to 70 cm at term. This extra-embryonic structure contains the main placental blood vessels (one vein and two arteries), the yolk stalk (omphalomesenteric duct), and the allantois.
There are essentially 3 separate aortic/venous circulatory systems: umbilical, systemic and vitelline. In the human cord, only the left placental (umbilical) vein persists, while the right placental (umbilical) vein degenerates. The initial segment of the cord at the "umbilicus" also contains the mid-gut herniation, present during the embryonic period of development.