Embryonic Structure
chorion Audio
cho·ri·on [ kawr-ee-on, kohr- ]
Subclass of:
Extraembryonic membranes
Etymology:
Greek chorion = membrane
A term first used for the outer layer of the fetal membranes by Galen.
Definitions related to chorion:
  • 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.
    NLM Medical Subject Headings
    U.S. National Library of Medicine, 2021
  • The outermost layer of the membranous sac enclosing the embryo in higher vertebrates.
    NCI Thesaurus
    U.S. National Cancer Institute, 2021
  • (egg chorion) A protective, noncellular membrane that surrounds the eggs of various animals including insects and fish.
    Gene Ontology Dictionary
    Gene Ontology Consortium, 2021
  • Chorion, in reptiles, birds, and mammals, the outermost membrane around the embryo. It develops from an outer fold on the surface of the yolk sac. In insects the chorion is the outer shell of the insect egg. In vertebrates, the chorion is covered with ectoderm lined with mesoderm (both are germ l...
    Encyclopedia Britannica
    Encyclopedia Britannica, Inc., 2020
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