<P> The amniotic sac , commonly called the bag of waters , sometimes the membranes , is the sac in which the fetus develops in amniotes . It is a thin but tough transparent pair of membranes that hold a developing embryo ( and later fetus ) until shortly before birth . The inner of these fetal membranes , the amnion , encloses the amniotic cavity , containing the amniotic fluid and the fetus . The outer membrane , the chorion , contains the amnion and is part of the placenta . On the outer side , the amniotic sac is connected to the yolk sac , the allantois and , via the umbilical cord , to the placenta . </P>
what is the function of the amniotic sac
the sac in which the fetus develops in amniotes