I990 



HUMAN ANATOMY. 



The human ovum when about to be Uberated from the Graafian follicle pos- 

 sesses a diameter of from .16-20 mm. Its cytoplasm, or vitellus, exhibits differ- 

 entiation into a peripheral protoplasmic and a central deutoplasmic zone. According 



to Nagel, within the former are to be 



Fig. 



distinguished a narrow 

 marginal 



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1688. 



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 ^-i^"^. 





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■T^i'x- 



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2y'^ 



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ta- 



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Almost mature human ovum taken from fresh ovary. Ovum, with 

 germinal vesicle and spot, is encircled by clear zona pellucida, which is 

 surrounded by cells of the follicular epithelium. > 300. (IValdeyer.) 



slight superficial 

 layer, apparently 

 homogeneous and free from 

 yolk-particles, and a finely 

 granular zone containing mi- 

 nute and scattered deutoplas- 

 mic granules. The dark or 

 central deutoplasmic zone is 

 conspicuous on account of 

 the irregular refraction of the 

 enclosed yolk-particles that 

 represent the important nutri- 

 tive materials for the embryo 

 contained in the eggs of birds 

 and reptiles, but which in the 

 mammalian ovum, especially 

 in that of man, have been for 

 the most part lost during the 

 evolution of the higher types. 

 Beyond a slight condensation 

 of the surface, the presence 

 of a distinct cell-wall, or vi- 

 telline membrane, in the mam- 

 malian ovum is doubtful. In 

 the fresh condition the egg- 

 cytoplasm is usually closely 

 applied to the zona pellucida 

 (Ebner), the narrow inter- 

 vening cleft that is sometimes seen being the perivitelline space. Embedded within the 

 deutoplasmic zone, and always eccentrically placed, lies the spherical germiyial vesicle, 

 as the egg-nucleus is termed. The vesicle measures from .030-045 mm. in diameter, 

 is bounded by a sharply defined double-contoured nuclear membrane, and contains 

 \h& germinal spot or nucleolus (from .004-. 008 mm.) and the nuclear reticulum. 



Corpus Luteum. — The causes leading to the final rupture of the Graafian 

 follicle are still uncertainly known, although in the light of later researches the older 

 view, attributing the bursting of the ripe vesicle to mechan- 

 ical overdistention induced by accumulation of the liquor 

 foUiculi, is inadequate. According to Nagel, when the 

 follicle approaches maturity the inner layer of the theca 

 becomes the seat of great activity. The blood-vessels in- 

 crease in size and number and the cells undergo not only 

 rapid proliferation, but extraordinary growth, the enlarged 

 elements becoming filled with a peculiar yellowish sub- 

 stance and transformed into luteiii cells. 



In consequence of this activity, the formerly smooth 

 theca becomes thickened and wavy and projects into the 

 cavity of the follicle as vascular papillae and ridges. The 

 encroachment thus efTected gradually forces the contents 

 of the vesicle towards the surface and that part of the dis- 

 tended follicular wall possessing least vitality and resist- 

 ance, until, finally, rupture takes place. Coincidently with 

 the proliferation of the lutein cells, the follicular epithelium 



undergoes fatty change which results in the breaking down of the cumulus and the 

 setting free of the ovum, encircled with the cells of the discus proligerus, into the 

 cavity of the egg-sac. When rupture of the follicle occurs, the expulsion of the 

 t.'g^ and the epithelial cells immediately surrounding it is followed by hemorrhage 



Fig. 1689. 



Corpus 

 luteum 



Graafian 



follicle 



Ligament 

 of ovary 



Ovary has been laid open by 

 longitudinal incision, exposing 

 follicles and corpus luteum. 



