obsolete_chorion true http://purl.obolibrary.org/obo/UBERON_0003124 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. James Malone 2.38 The chorion is one of the membranes that exists during pregnancy between the developing fetus and mother. It is formed by extraembryonic mesoderm and the two layers of trophoblast and surrounds the embryo and other membranes. true BTO:0000252 Use http://purl.obolibrary.org/obo/UBERON_0003124 label: chorion