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the outermost fetal membrane in human embryos, the villous part of which becomes the fetal part of the placenta.
Synonym(s): chorionic vesicle
Etymology: Gk, chorion, skin, sakkos, sack
the saclike membrane that develops from the blastocyst wall to envelop the embryo.
The outer fetal membrane that encloses the developing embryo.
See also: sac