The age-old debate of whether the chicken or the egg came first is explored through historical and evolutionary contexts.

In placental mammals, the chorion and the allantois together form the fetal side of the mature placenta. This is a chorioallantoic placenta. Chorion forms part of fetal tissue, allantois becomes ...

The fetal membranes consist of the chorion, amnion, yolk sac, and allantois. The chorion has three layers: cytotrophoblastic, chorionic connective tissue, and basement membrane. The chorion lies ...