<Tr> <Th> Dorlands / Elsevier </Th> <Td> s_01 / 12716695 </Td> </Tr> <Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <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> <P> Amniocentesis is a medical procedure where fluid from the sac is sampled to be used in prenatal diagnosis of chromosomal abnormalities and fetal infections . </P>

What is the function of the amniotic sac