chorion membrane http://upload.wikimedia.org/wikipedia/commons/5/51/Gray24.png NCIT:C34124 NCIT:C34122 CALOHA:TS-0144 The chorion of placentals is bilaminar as in reptiles and birds, but forms from the trophoblast and includes the ajdacent mesodermal layer [ISBN:0073040584] Extra-embryonic ectoderm EV:0100121 The outermost extraembryonic membrane of amniotes. uberon chorion frondosum fetal chorion The outer membrane enclosing the embryo in reptiles, birds, and mammals. [TFD][VHOG] uterine chorion EMAPA:16112 MESH:A16.254.403.473 chorion (vertebrates) EHDAA2:0000245 EHDAA:150 chorionic VHOG:0000200 Structures homologous to the four extraembryonic membranes of reptiles and birds appear in mammals: amnion, chorion, yolk sac, and allantois.[well established][VHOG] embryonic chorion UMLS:C0008503 EFO:0002780 UMLS:C1516505 UBERON:0003124 chorion GAID:1299 The outer membrane of the two membranes enclosing the embryo in reptiles, birds, and mammals. In placental mammals it contributes to the development of the placenta[BTO:0000252]. chorionic sac BTO:0000252 This term refers to the amniote structure. It is distinct from the concept of chorion in insects FMA:80224 mesoderm-derived structure extraembryonic membrane