518 THE REPRODUCTIVE SYSTEM 



ovum in the form of a hillock, the so-called cumulus oophorus. The 

 latter term is now generally used exclusively in a sense to include and 

 displace the term discus proligerus. 



The cells of the cumulus, which adjoin the zona pellucida, become 

 somewhat elongated and in this way they form a radiate investment con- 

 sisting of one or two rows of columnar cells which surround the zona 

 pellucida of the ovum and are known as the corona radiata. With the 

 increase of the liquor folliculi the cumulus with its contained ovum is 

 soon separated from its attachment to the stratum granulosum and the 

 development of the folliculi is complete. 



During this period of rapid growth and development the follicle 

 has increased in size from a diameter which scarcely exceeded that of its 

 ovum (about 300 /*) to such a size that it occupies the entire breadth of 

 the ovarian cortex. It is now ready for the final steps in the maturation 

 of its ovum and for the rupture of the follicle coincident with the ap- 

 proach of the menstrual period. 



The forces which lead to the rupture of the follicle are not fully 

 determined. They are undoubtedly varied, and, in addition to the 

 gradual attentuation of the layer of cortical stroma which covers the 

 free surface of the follicle and is known as the stigma, they include the 

 gradual accumulation of liquor folliculi under increasing tension, the 

 marked congestion of the ovary at the approach of the menstrual period, 

 which is accompanied by the determination of an undue proportion of 

 blood to the theca of the ripe follicle (Clark), and possibly the contrac- 

 tion of the smooth muscle contained in the stroma of the deeper part of 

 the cortex and adjacent portions of the medulla. In any event, as a 

 result of the independent or combined action of these, or other unknown 

 forces, the follicle ruptures in the direction of least resistance, viz., at 

 the attenuated stigma, and the liquor folliculi gushes forth, carrying 

 with it the detached ovum invested with its cumulus. The ovum is 

 now free to enter the oviduct and prepare itself for fertilization and the 

 development of the future embryo. 



The ovum finds its way from the abdominal cavity into the oviduct by 

 aid of currents established in the direction of the orifice by the cilia of 

 the cells covering the fimbriae; perhaps assisted by a direct grasping 

 activity on the part of the fimbriae. Since spermatozoa are free to wan- 

 der out of the oviduct into the abdominal cavity, and since an egg may 

 occasionally fail to reach the opening of the oviduct, the possibilities are 

 offered for an abdominal pregnancy, a result occasionally consummated. 

 Likewise an egg may fail to become expelled from its follicle and may 



