Explanation:
Antrum is a cavity that is found in the Graafian follicle. The Graafian follicle is a structure in the ovary that develops and matures during the menstrual cycle. It is responsible for producing and releasing a mature egg during ovulation.

Graafian Follicle:
- The Graafian follicle is the most mature follicle in the ovary.
- It is named after Regnier de Graaf, a Dutch physician who first described it in the 17th century.
- It develops from a primordial follicle, which is a small, immature follicle.
- The development of the Graafian follicle is regulated by hormones such as follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
- As the follicle grows, it secretes estrogen, which prepares the uterus for possible implantation of a fertilized egg.

Antrum:
- As the Graafian follicle matures, it develops a fluid-filled cavity called the antrum.
- The antrum is formed as a result of the accumulation of follicular fluid secreted by the cells surrounding the oocyte (egg).
- It appears as a large, fluid-filled space within the follicle.
- The antrum provides a supportive environment for the oocyte and helps in its maturation.
- It also plays a role in the release of the oocyte during ovulation.

Function of Antrum:
- The antrum provides a protective and nourishing environment for the oocyte.
- It helps in the maturation of the oocyte by supplying necessary nutrients and hormones.
- The antrum also plays a crucial role in the release of the oocyte during ovulation.
- During ovulation, the antrum expands and ruptures, allowing the mature oocyte to be released into the fallopian tube.

Conclusion:
In conclusion, the antrum is a cavity that is found within the Graafian follicle. It plays a crucial role in the maturation and release of the oocyte during ovulation.