part_of part of part of develops_from develops from develops from organ female reproductive system uterus placenta allantoic placenta eutherian placenta organ of metabolic interchange between fetus and mother, partly of embryonic origin and partly of maternal origin[GO]. The fetal portion of the placenta is known as the villous chorion. The maternal portion is known as the decidua basalis. The two portions are held together by anchoring villi that are anchored to the decidua basalis by the cytotrophoblastic shell. chorion membrane mesoderm-derived structure allantois reproductive structure entire extraembryonic component