That portion of the chorionic wall in the region of its uterine attachment, which gives rise to chorionic villi; it consists of the mesoderm that lines the chorionic vesicle and, on the maternal side, of the trophoblast that lines the intervillous spaces; in the last half of gestation, the mesodermal connective tissue is largely replaced by fibrinoid material, and the amnionic membrane is adherent to the fetal side of the plate. [ http://www.medilexicon.com/medicaldictionary.php?t=69523 ]