540 MANUAL OF HISTOLOGY. 



and partly around the latter, enveloping them in a manner which reminds 

 one of the mode of formation of the walls of vessels already described 

 (211), (His). 



The Graafian follicle is distended by that fluid, the commencement of 

 whose formation we have already alluded to above. It is transparent, 

 alkaline in reaction, and contains albumen. It is known as the liquor 

 folliculi. The round nucleated cells covering the internal surface of the 

 cavity, in ill-defined layers, are known, taken as a whole, as the formatio 

 or membrana granulosa : the elements measure individually about from 

 0*0074 to O'OllS mm. The breaking down or solution of the latter may 

 account for the presence of albumen in the fluid. The point at which 

 this stratum attains its greatest depth, in order completely to surround the 

 egg (cumulus proligerus of embryologists, cumulus ovigerus of Koelliker), 

 was formerly supposed to be at that aspect of the follicle nearest to the 

 periphery of the organ. More accurate and recent observation has, how- 

 ever, shown this view to be erroneous, and that the ovule is attached 

 to that side of the follicular cavity, as a rule, which is most remote from 

 the surface of the ovary (Schron., His). It may, however, be found in th.e 

 first position ( Waldeyer). 



The mature ovum (fig. 533, 1, 2) is still of great minuteness^ and 

 therefore not easy to find. In order the better to investigate its nature 

 we are obliged, in the first instance, to free it from the elongated cells of 

 the membrana granulosa, fixed upon it in a radiating manner (2, c). It 

 is then found to be a spherical structure from 0'28 to 0*1379 mm. in 

 diameter, or, in other words, a beautifully developed cell with a thickened 

 capsule. All these different parts have received names from the anato- 

 mists of former times. 



The capsule, in the first place, is known as the zona peRucida or cliorion. 

 It presents itself as a soft, transparent, semi-solid substance, homogeneous 

 in appearance, in all probability pierced, nevertheless, by minute pores 

 (fig. 73, p. 83). It is now about 0-0090-0-0113 mm. in thickness. Its 

 origin is at present unknown. It may either be formed by the ovum 

 itself, or deposited upon the latter from without. The latter, in our 

 opinion, is the most plausible hypothesis. 



Chemically it is a substance difficult of solution in alkalies, resembling 

 elastin in a great measure. 



The cell body (&), possessing a hardened cortical layer, appears in man 

 and the mammalia as a more or less opaque mass, containing in a viscid 

 substratum molecules of coagulated albuminous matters, as well as granules 

 and globules of fatty substances. It is known as the vitellus. 



The nucleus (1, c), generally known under the name of the vesicula 

 germinativa, or germinal vesicle of Purkinje, is situated in the mature 

 ovum excentrically. It is a very delicate and perfectly spherical vesicle 

 of 0'037-0'0451 mm. in diameter, quite transparent, and presents a 

 round and highly refracting nucleolus (d), from 0*0046 to 0*0068 mm. in 

 diameter. The latter has received the name of the macula germinativa, 

 or germinal spot of Wagner. 



Let us now turn to the blood and lymphatic vessels of the ovary. 



We have already been obliged to refer to the blood-vessels in the fore- 

 going description. They arrive at the hilus in the form of large arterial 

 and venous twigs, the former taking a very tortuous spiral course on 

 their way thither. Arrived in the stroma they break up into numerous 

 branches, so that the medullary substance of the latter is, in reality, a 



