The follicular antrum is the portion of an ovarian follicle filled with follicular fluid. Appearance of the follicular antrum during follicular maturation is the first sign that a follicle has reached the next stage of maturation. It has changed from a primary follicle to a secondary follicle.
- Histology at KUMC female-female07 "Graafian Follicle"
- Anatomy photo: Reproductive/mammal/ovary2/ovary2 - Comparative Organology at University of California, Davis - "Mammal, canine ovary (LM, High)"
- Description at okstate.edu