HISTOLOGY 151 



At this stage the ovum is free in the cavity of the mature follicle, sur- 

 rounded by the cells of the cumulus oophorus. Ovulation occurs soon after 

 this condition is established. 



Parallel with the changes taking place in the ovum, changes also occur 

 in the surrounding tissues. The large blood vessels of the medulla are 

 engorged and the capillaries around the Graafian follicles show congestion. 

 The thin wall of each follicle protruding into the periovarian space consists 

 of flattened germinal epithelium, stretched tunica albuginea, the cells of 

 which seem to be loosened by the congested capillaries, and one or two rows 

 of granulosa cells. The opposite wall is considerably thicker, consisting of 

 many layers of granulosa cells, and the theca interna which in section 

 appears to project in waves into the follicle. When the thin wall ruptures, 

 the ovum with the first polar body and the second polar spindle in the 

 process of formation, surrounded by the cells of the cumulus oophorus, 

 imbedded in liquor folliculi, are expelled into the periovarian capsule which, 

 consequently, becomes distended. Several ova escape in a relatively short 

 time interval, and due to the viscosity of the liquor folliculi they have a 

 tendency to clump. They remain in the periovarian capsule only for a very 

 short time, passing almost at once into the ampulla of the oviduct, which 

 becomes distended. Fertilization takes place here and if spermatozoa enter 

 the ova, the second divisions are completed. If fertilization does not take 

 place, further development does not occur and the ova fragment and 

 degenerate. 



The ruptured follicle and the formation of the corpus leuteum. — After 

 the bulging wall of the follicle has ruptured the tension is relieved and 

 only a relatively small gap and cavity remain. The rupture does not 

 cause bleeding, and normal ovulation is seldom followed by the formation 

 of a hemorrhagic follicle. The free surface of the ruptured area contains 

 enlarged capillaries, and the rich blood supply probably facilitates the 

 rapid healing (Fig. 78). About 2 hours after ovulation the germinal epi- 

 thelium and the tunica albuginea are united and the rupture is closed. 

 From this time on the follicle is called the corpus luteum. In the young 

 corpus luteum the theca externa keeps its circular outline, w^hile the cells 

 of the theca interna, which were beginning to project into the follicle even 

 before ovulation, now penetrate still farther, carrying with them a network 

 of developing capillaries, and are thus converted into vascular, radially 

 arranged trabeculae providing support and blood supply to the granulosa 

 cells. The trabeculae extend to the small inner cavity in which they form a 

 loose network (Fig. 79). Later when the lutein cells are fully hypertrophied 



