The fluid-filled cavity in an ovarian follicle is termed

As the ovarian follicle develops, a fluid-filled cavity known as the antrum forms within the follicle. This antrum contains follicular fluid and surrounds the developing oocyte. The amnion is a membrane that surrounds the developing foetus during pregnancy. The term ventricle refers to a fluid-filled cavity within the brain. It can also refer to a lower chamber of the heart. The term lacuna refers to a small space within the matrix of bone (or cartilage) that encloses one osteocyte (or one to four chondrocytes).