THE OVARIES. 1989 



centrically disposed connective-tissue fibres, and an inner (tunica interna), composed of round 

 and spindle cells, and provided with numerous capillaries. After the follicular epithelium has 

 been formed, the ovum itself begins to grow, the expansion proceeding uniformly and affecting 

 all parts of the cell, including nucleus and nucleolus. It attains its maximum diameter com- 

 paratively early and long before the follicle has reached full growth. Through the agency of 

 the follicular epithelium, the egg becomes invested with a protecting envelope, the zona 

 pellucida, after which little or no further increase in the size of the ovum takes place (Nagel). 



At first solid, the growing follicle is converted into a vesicle containing fluid by the 

 vacuolation and breaking down of cells within the middle layers of the follicular epithelium, the 

 resulting clefts fusing into a common space. The intra-epithelial cavity so formed contains 

 accumulating fluid, the liquor folliculi, that is supplied by the continued proliferation, vacuolation, 

 and destruction of the follicle cells and by the transudation from the surrounding blood-vessels. 

 This fluid increases in amount to such an extent that it soon occupies the greater part of the 

 expanding egg-sac, now entering upon its final stage of growth. 



The maturing follicles (folliculi oophori vesiculosi) occupy the deeper parts of the cortex 

 and reach to the medulla. With their expansion and consequent requirement of space, the 

 vesicles seemingly rise, appropriating more and more of the cortex, until the entire thickness of 

 the latter, and sometimes a part of the medulla in addition, is occupied by the ripe follicle, 

 which just before its final rupture attains a diameter of from 1-2 cm. or more, and appears on the 



FIG. 1687. 



Surface epithelium ^SK^SSOf^f^^^ 



Primary follicles 



Theca of follicle V"rr 



Stratum rx 

 granulosum , , 



Discus 7* 

 proligerus 



Zona pellucida^ 



Cavity filled by liquor folliculi 

 Section of ovary, showing partially developed Graafian follicle. X 100. 



free surface of the ovary as a tense rounded elevation. After liberation of the ovum, the folli- 

 cle is converted into the conspicuous corpus luteum (page 1990). 



Seen in section, the wall of the ripe follicle, now known as the Graafian follicle, consists 

 of a well-developed capsule or theca (from .14-. 20 mm. in thickness), of which the outer layer 

 is a lamellated fibrous membrane, and the inner tunic is composed of looser connective tissue 

 containing numerous peculiar large cells which, as maturity approaches, exhibit granularity and 

 a faint yellowish color. Next the inner layer of the capsule lies a delicate membrana propria, 

 against the inner surface of which is applied the stratum gramilosum, composed of the outer 

 layers of the follicular epithelium that bound externally the fluid-space of the vesicle. At one 

 point, always opposite the place where the follicle ruptures (stigma), the stratum granulosum is 

 prolonged into a pedunculated spherical mass of epithelial cells that projects into the cavity 

 occupied by the liquor folliculi. This mass (cumulus oophorus) contains the egg and on section 

 appears as a ring (discus proligerus} that encircles the zona pellucida and the enclosed ovum 

 and consists of two or three layers of epithelial cells. Those next the zona are elongated, with 

 their ends directed towards the ovum pointed and prolonged into delicate processes that are 

 attached to or penetrate within the zona pellucida. The latter, from .007-. on mm. in thickness, 

 is the product of the surrounding follicular cells and does not form a part of the ovum proper. 

 The radial striations which the envelope sometimes exhibits (hence the name, zona radiata, 

 under which it is often described) are probably due to the processes of the epithelial cells and 

 not to the existence of minute canals (micropyles) seen in the eggs of many lower animals. 



