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The Endowment for Human Development
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Amniotic Fluid


4 weeks, 4 days

From The Biology of Prenatal Development.Buy Now

Script: By 4 weeks the clear amnion surrounds the embryo in a fluid-filled sac. This sterile liquid, called amniotic fluid, provides the embryo with protection from injury.

All ages referenced to fertilization, not last menstrual period.
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Sections of the Brain
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Body Cavity Formation
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