Menstrual cycle anatomy. 1866 illustrations showing the internal anatomy of a human ovary containing Graafian (ovarian) follicles (Fig. 1.), Graafian follicle (Fig. II), ovulation of an egg cell (ovum, Fig. III), ovum (Fig. IV) and corpus luteum (Fig. V). The Graafian follicles are vesicles that each contain a single ovum and also secrete hormones that influence the stages of the menstrual cycle. During ovulation an ovum is released from the ovary and travels to the uterus (womb) to be fertilised). The corpus luteum develops from a Graafian follicle following the release of an ovum and is essential for establishing and maintaining pregnancy. It secretes progesterone, a hormone responsible for the development and maintenance of the lining of the uterus (endometrium).