This page discusses embryo development in reptiles, birds, and mammals, focusing on four extraembryonic membranes: amnion, yolk sac, chorion, and allantois, which support the embryo. It categorizes ma...This page discusses embryo development in reptiles, birds, and mammals, focusing on four extraembryonic membranes: amnion, yolk sac, chorion, and allantois, which support the embryo. It categorizes mammals into monotremes, marsupials, and placental mammals, highlighting that humans belong to the placental group, where the placenta connects the embryo to the mother.