The chorion is a vital membrane that surrounds the developing embryo in mammals, including humans. It plays a crucial role in the formation of the placenta, which provides nutrients and oxygen to the growing fetus while removing waste products. The chorion is composed of trophoblast cells that facilitate the attachment to the uterine wall. In addition to its role in placental development, the chorion also contributes to the formation of the amniotic sac, which protects the embryo by providing a cushioning environment. Together with other membranes, the chorion helps ensure a safe and supportive environment for fetal development throughout pregnancy.