Tags: Anatomical Structure, Embryology.
The amniotic sac (also bag of waters) is the sac in which the fetus develops in amniotes. It is a thin but tough transparent pair of membranes which hold a developing embryo (and later fetus) until shortly before birth. The inner membrane the amnion contains the amniotic fluid and the fetus. The outer membrane the chorion contains the amnion and is part of the placenta. Its wall is the amnion the inner of the two fetal membranes. It encloses the amniotic cavity and the embryo.
