<unk>  are<unk>  that sprout from the chorion in order to give a maximum area of contact with the maternal blood.
Embryonic blood is carried to the<unk>  by the branches of the umbilical arteries, and after circulating through the capillaries of the<unk> , is returned to the embryo by the umbilical veins.
Thus, the<unk>  are part of the border between maternal and fetal blood during pregnancy.
Chorionic villi
Decidua
Atrophodermia Vermiculata
Serous membrane
Amniotic sac
Microtia
Yolk sac
Blastocyst