Last revised by Grace Carpenter on 29 Jan 2022

The chorion is one of the embryonic membranous structures that encloses the fetus and the amnion. The chorion begins to form chorionic villi towards its outer surface, which initially serves to provide nutrition to the developing embryo. 

Part of the chorionic villi arborize more extensively and forms the chorionic frondosum, which in turn gives rise to the placenta. 

History and etymology

The word chorion derives from the Greek word χόριο meaning skin. Galen was the first to apply the term to the fetus.

Related pathology

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