Amnion: Introduction
Amnion is the term for t he innermost fetal membrane; a thin, transparent sac that holds the fetus suspended in the liquor amnii , or amniotic fluid. The amnion grows rapidly at the expense of the extraembryonic coelom, and by the end of the third month , it fuses with the chorion, forming the amniochorionic sac. It is commonly known as “the bag of waters”.