Definition of amnion in English:

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Pronunciation: /ˈamnēän/
Pronunciation: /ˈamnēən/

noun (plural - or amnionia /-nēə/)

The innermost membrane that encloses the embryo of a mammal, bird, or reptile.
Example sentences
  • Inside the egg are a series of fluid-filled membranes which permit the embryo to survive: the amnion, allantois, yolk sac, and chorion.
  • The middle part of the streak gives rise mainly to lateral plate mesoderm, while the posterior part of the streak provides the extra-embryonic mesoderm of the amnion, visceral yolk sac, and allantois.
  • We're talking about things like the amnion, the chorion, the allantoic sac, the placenta, the umbilical cord, if those words sound familiar to you.


Mid 17th century: from Greek, 'caul', diminutive of amnos 'lamb'.

For editors and proofreaders

Syllabification: am·ni·on

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