The chorion.
trophoblast
chorion
chorion
The placenta is completely formed by 10 weeks, by the joining of the decidua basalis (maternal side) and chorionic villi (fetal side). The chorion and amnion are the placental membranes. The Chorion is the membrane furthest from the embryo, and the amnion in the inner layer that is closest to the embryo.
The allantois membrane and the chorion form the placenta in mammals. The chorion is the outermost fetal membrane that encases the embryo and later fuses with the maternal tissue to form the placenta.
The chorion develops into the fetal portion of the placenta. It plays a crucial role in nutrient and gas exchange between the mother and the fetus during pregnancy.
from the chorion frondosum of the fetus and the decidua basalis of the mother
Allantois, amnion, and chorion
The chorion is the outermost membrane surrounding the embryo, while the trophoblast is the outer layer of cells of the blastocyst responsible for implantation and placenta formation in early pregnancy. Specifically, the trophoblast gives rise to the chorion during embryonic development.
The allantois, yolk sac and part of chorion.
The allantois, yolk sac and part of chorion.