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decidua (di-sid-yoo-ă) n. the modified mucous membrane that lines the wall of the uterus during pregnancy and is shed with the afterbirth at parturition (see endometrium). d. basalis the region of the decidua where the embryo is attached. d. capsularis the thin layer of the decidua that covers the embryo. d. parietalis the region of the decidua that is not in contact with the embryo.
decidual adj.