Source:http://linkedlifedata.com/resource/umls/id/C0008503
MSH: The outermost extra-embryonic membrane surrounding the developing embryo. In REPTILES and BIRDS, it adheres to the shell and allows exchange of gases between the egg and its environment. In MAMMALS, the chorion evolves into the fetal contribution of the PLACENTA.,NCI: The outermost layer of the membranous sac enclosing the embryo in higher vertebrates.