from The American Heritage® Dictionary of the English Language, 4th Edition
- n. Any of the membranous structures closely associated with or surrounding a developing vertebrate embryo, including the amnion, chorion, allantois, and yolk sac.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. the inner membrane of embryos in higher vertebrates (especially when covering the head at birth)
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