what forms the embryonic placenta
The placenta is composed of both maternal tissue and tissue derived from the embryo. The chorion is the embryonic-derived portion of the placenta. It is composed of trophoblasts, which you may remember are the cells that made up the outer cell layer of the blastocyst.he placenta is composed of both maternal tissue and tissue derived from the embryo. The chorion is the embryonic-derived portion of the placenta. It is composed of fetal blood vessels and trophoblasts which are organized into finger-like structures called chorionic villi.