Amnion

[æmniәn]

(noun.) thin innermost membranous sac enclosing the developing embryo of higher vertebrates (reptiles, birds and mammals).

Inputed by Glenda--From WordNet

(n.) A thin membrane surrounding the embryos of mammals, birds, and reptiles.

Inputed by Heinrich

n. the innermost membrane enveloping the embryo of reptiles birds and mammals.

Checker: Paulette