The outer membrane (chorion) and trophoblast layer of the placenta are derived from the trophoectoderm of the blastocyst cells. Other extra-embryonic tissues, including the amnion (inner membrane ...

The inner of these membranes, the amnion, encloses the amniotic cavity, containing the amniotic fluid and the embryo. The outer membrane, the chorion, contains the amnion and is part of the placenta.