Tags: Anatomical Structure.
For the chorion in vertebrate eggs see Chorion (egg).For the entertainment company see Chorion (company).In humans and most mammals the chorion is one of the membranes that exist during pregnancy between the developing fetus and mother. It is formed by extraembryonic mesoderm and the two layers of trophoblast and surrounds the embryo and other membranes. The chorionic villi emerge from the chorion invade the endometrium and allow transfer of nutrients from maternal blood to fetal blood.
