<P> The chorion is the outermost fetal membrane around the embryo in mammals , birds and reptiles . It develops from an outer fold on the surface of the yolk sac , which lies outside the zona pellucida ( in mammals ) , known as the vitelline membrane in other animals . In insects it is developed by the follicle cells while the egg is in the ovary . The main function of the chorion is to protect and nurture the embryo . </P>
<P> The chorion is the outermost fetal membrane around the embryo in mammals , birds and reptiles . It develops from an outer fold on the surface of the yolk sac , which lies outside the zona pellucida ( in mammals ) , known as the vitelline membrane in other animals . In insects it is developed by the follicle cells while the egg is in the ovary . The main function of the chorion is to protect and nurture the embryo . </P>
the extraembryonic membrane that helps in the formation of the placenta is the
the extraembryonic membrane that helps in the formation of the placenta is the
chorion
chorion