Antrum is found in:
Antrum is a fluid filled cavity found in the tertiary follicle.
Follicles are formed inside the ovary. The various follicles formed inside the ovary include: primary follicle, secondary follicle, tertiary follicle and Graafian follicle (mature follicle).
Primary follicle consists of a primary oocyte enclosed by a layer of granulosa cells.
The primary follicle transforms into a secondary follicle which is surrounded by many layers of granulosa cells and a new theca layer.
The secondary follicle transforms into tertiary follicle in which a cavity develops called antrum. The theca gets differentiated into an outer theca externa and an inner theca interna. Inside the tertiary follicle, the primary oocyte completes meiosis I and forms into the secondary oocyte.
The tertiary follicle transforms into a mature Graafian follicle that gets ruptured to release the secondary oocyte.