Embryonic Structure
amnion Audio
am·ni·on [ am-nee-uhn ]
Subclass of:
Extraembryonic membranes
Etymology:
Greek amnion = bowl in which sacrificial blood was collected
Definitions related to amnion:
  • Extraembryonic membrane which contains the embryo and amniotic fluid.
    CRISP Thesaurus
    National Institutes of Health, 2006
  • The innermost layer of membrane that surrounds an embryo and amniotic fluid in mammals, birds, and reptiles.
    NCI
    U.S. National Cancer Institute, 2021
  • The innermost membranous sac that surrounds and protects the developing embryo which is bathed in the AMNIOTIC FLUID. Amnion cells are secretory EPITHELIAL CELLS and contribute to the amniotic fluid.
    NLM Medical Subject Headings
    U.S. National Library of Medicine, 2025
  • Amnion, in reptiles, birds, and mammals, a membrane forming a fluid-filled cavity (the amniotic sac) that encloses the embryo. The amniotic sac and the fluid it contains are sometimes referred to as the bag of waters. In development, the amnion arises by a folding of a mass of extra-embryonic...
    Encyclopedia Britannica
    Encyclopedia Britannica, Inc., 2025
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