chorion frondosum

Thus the placenta develops from the chorion frondosum and the decidua basalis.

The decidual plate is tightly attached to the chorion frondosum and goes on to form the actual placenta.

Chorionic villi (from the embryo) on the embryonic pole grow, forming chorion frondosum.

The endometrium (from the mother) over the chorion frondosum (this part of the endometrium is called the decidua basalis) forms the decidual plate.

On the other hand, the villi at the embryonic pole, which is in contact with the decidua basalis, increase greatly in size and complexity, and hence this part is named the chorion frondosum.

The placenta functions as a fetomaternal organ with two components: the fetal placenta (Chorion frondosum), which develops from the same blastocyst that form the fetus, and the maternal placenta (Decidua basalis), which develops from the maternal uterine tissue.