Chorion Frondosum

The chorion frondosum is the embryonic portion of the placenta. It consists of finger-like projections, or villi, of the chorion's surface. The chorion frondosum extends to meet the maternal portion of the placenta, which is composed of the intervillous pool of maternal blood from material arteries and veins; this allows for diffusion of oxygen and of waste gases (such as carbon dioxide) between the membranous layers through a supply of arterial and venous blood from the maternal vessels.