There is no such thing as an "ovarian sac".
The amnion is a membrane building the "amniotic sac" that surrounds and protects an embryo.
Ovary
The Amnion or the Amniotic Sac
the amnion
The inner cell mass (ICM) produces three embryonic membranes, the amnion, allantois, and the yolk sac.
an amnion
its amnion
Amniotic sac
Amnion
The inner most membrane is the fluid filled amniotic sac, next is the yolk sac, where the first blood cell originates. The allantois forms near the yolk sac, while the chorion surrounds all the other ones.
Amnion chorion yolksac allantois
Ovary
Ovarian follicle