1) Biological tissues 2) Coverings 1) Septa 
The sac or 'bag of waters' filled with amniotic fluid in which the developing baby grows. The 'membranes' which make up the sac may occasionally rupture naturally as labour begins, but usually remain intact until the end of the first stage of labour. The membranes may also be broken by a midwife or doctor to speed up labour.
Thin layers of tissue which cover parts of the body, separate adjacent cavities, or connect adjacent structures. ... (12 Dec 1998) ... 
The sac that surrounds the baby in the uterus
The amnion and chorion, which make up the amniotic sac
The sac that surrounds the baby in the uterus and contains amniotic fluid in which the baby floats. Also called the bag of waters or amniotic sac, the membranes will rupture naturally or be ruptured artificially during labor.