vitellochorion

vitellochorion

an intermediate stage in the development of a yolk sac type of placentation. The outer chorion of the embryo must be vascularized by an extraembryonic circulatory system in order to establish an organ of interchange between the dam and the fetus. If this is provided by the yolk sac vessels a vitellochorion is established. If the vascularization is by allantoic vessels the placentation is an allantochorion.
Mentioned in ?