242 MICROSCOPIC ANATOMY OF THE 



ing the follicle, and partly to a liquefaction of certain of the 

 follicular cells. In consequence of the increase in this fluid the 

 ovum is pushed to one side (Fig. 185), and the whole Granji<ui 

 follicle (folliculus oophorus vesiculosus) becomes as large as 

 5 mm. in diameter, and is seen bulging from the surface of the 

 ovary. 



The follicular epithelium lining the interior of the follicle 

 in many layers is known as the stratum granulosum (membra n a 

 granulosa). At one place it forms a hill-like mass, which con- 

 tains the ovum (Fig. 185), and is known as the cumulus 

 oophorus or discus proligerus. At this period the membrana 

 pellucida surrounding the ovum becomes thicker and shows a 

 radial striation, which was at first thought to be due to a system 

 of pores running through the membrane. Later investigators 

 (Paladino and Retzius) claim that the striation is caused by the 

 passage of fine processes of the follicular cells through the zona 

 pellucida, after the manner of protoplasmic bridges. In this 

 way there is established a close connection between the ovum 

 and the follicular cells, which is of importance in the nourish- 

 ment of the egg cell. 



Between the ovum and the zona pellucida there is a small 

 space, known as the periviieUine space. Thus the ovum may 

 turn inside the zona pellucida. Sabotta has described the zona 

 pellucida in the mouse as a quite homogeneous membrane with- 

 out any striation whatever, and disputes also the existence of a 

 perivitelline space. 



Outside the zona pellucida there is a layer of cylindrical fol- 

 licular cells arranged radially. These form the so-called corona 

 radiata. The whole Graafian follicle is surrounded by a con- 

 nective-tissue capsule, the theca folliculi. Between this and 

 the follicular epithelium there is a structureless basal membrane 

 (membrana propria folliculi, Glashaut). In the theca folliculi 

 there are to be distinguished two layers: the tunica interna, 

 consisting of round or spindle-shaped cells ; and the tunica 

 externa, which is made up of circularly disposed connective- 

 tissue fibres. 



The formation of the Graafian follicle begins before puberty, 



