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 ...

Other extra-embryonic folds expand up over the embryo to form the amniotic folds. The amnion and chorion develop together as upwardly projecting amniotic folds, eventually closing over the dorsal ...