chorion defined in 1951 yearchorion - chorion;
chorion - (Zool.). Embryonic membrane of amniote vertebrate, consisting of outer ectodermal epithelium with layer of mesoderm beneath. In Sauropsida, the more superficial of the two layers which enclose the amniotic cavity. See also: Amnion. In mammals, the superficial layer enclosing all the embryonic structures (equivalent therefore to sauropsid chorion plus outer layer of yolk-sac); its outer epithelium is trophoblast; forms placenta. (2) Non-cellular membrane secreted around ovum by cells of ovary, e.g. the superficial envelope or 'shell' of an insect egg.
near chorion in Knolik
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