Amnion

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Amnion
Chicken egg with amnion surrounding the embryo
Human fetus, enclosed in the amnion.
Details
Identifiers
Latin	amniosinas
MeSH	D000650
TE	E6.0.1.2.0.0.9
FMA	80223
Anatomical terminology [edit on Wikidata]

Look up amnion in Wiktionary, the free dictionary.

The amnion (pl.: amnions or amnia) is a membrane that closely covers human and various other embryos when they first form. It fills with amniotic fluid, which causes the amnion to expand and become the amniotic sac that provides a protective environment for the developing embryo. The amnion, along with the chorion, the yolk sac and the allantois protect the embryo. In birds, reptiles and monotremes, the protective sac is enclosed in a shell. In marsupials and placental mammals, it is enclosed in a uterus.

The amnion is a feature of the vertebrate clade Amniota, which includes reptiles, birds, and mammals. Amphibians and fish lack the amnion and thus are anamniotes (non-amniotes). The amnion stems from the extra-embryonic somatic mesoderm on the outer side and the extra-embryonic ectoderm or trophoblast on the inner side.^[1]