Chorion
The chorion is one of the fetal membranes that forms between the developing fetus and mother during pregnancy. Both chorion and endometrium form the placenta, which is the embryo’s principal organ of respiration, nutrition, and excretion.Chorion is covered with ectoderm, lined with mesoderm and is separated from other embryonic membranes by the coelom. Chorion develops a rich supply of blood vessels and forms an intimate association with the endometrium (lining) of the mother’s uterus.