754 FEMALE ORGANS OF GENERATION. 



a network of bloodvessels ; and an internal coat, named the ovi-capsule, which ig 

 lined by a layer of nucleated cells, called the membrana granulosa. The fluid 

 contained in the interior of the vesicles is transparent and albuminous, and in it 

 is suspended the ovum. 



The Ovum is a small spherical body, situated, in immature vesicles, near their 

 centre ; but, in the mature ones, in contact with the membrana granulosa, at that 

 part of the vesicle which projects just beneath the surface of the ovary. Accu- 

 mulated round the ovum, in greater number than at any other point, are the cells 

 of the membrana granulosa, forming a kind of granular zone, the discus proli- 

 gerus. 



The human ovum is extremely minute, measuring from 5 | 7 to yj^ of an inch 

 in diameter. It consists, externally, of a transparent envelop, the zona pellucida 

 or vitelline membrane ; within this, and in close contact with it, is the yelk or 

 vitellus ; imbedded in the substance of the yelk, is a small vesicular body, the 

 germinal vesicle, which contains the germinal spot. 



The zona pellucida or vitelline membrane is a thick, colorless, transparent 



membrane, which appears under the mi- 

 Fig. 379. Ovum of the Sow. croscope as a bright ring, bounded ex- 

 ternally and internally by a dark outline. 

 It corresponds to the chorion of the im- 

 pregnated ovum. 



The ydk consists of g raimles and g ] - 

 bules of various sizes, imbedded in a more 



or less viscid fluid. The smaller gra- 

 nules resemble pigment ; the larger gra- 

 nules, which are in greatest number at 

 the periphery of the yelk, resemble fat- 

 globules. In the human ovum, the number of granules is comparatively small. 



The germinal vesicle consists of a fine, transparent, structureless membrane, 

 containing a watery fluid, in which are occasionally found a few granules. It is 

 about fj\^ f an inch in diameter, and, in immature ova, lies nearly in the centre 

 of the yelk ; but, as the ovum becomes developed, it approaches the surface, and 

 enlarges much less rapidly than the yelk. 



The germinal spot occupies that part of the periphery of the germinal vesicle 

 which is nearest to the periphery of the yelk. It is opaque, of a yellow color, 

 and finely-granular in structure, measuring from -jg 1 ^ to s^Vs- of an inch. 



The formation, development, and maturation of the Graafian vesicles and ova 

 continue uninterruptedly from infancy to the end of the fruitful period of 

 woman's life. Before puberty, the ovaries are small, the Graafian vesicles con- 

 tained in them minute, and few in number ; and few, probably, ever attain full 

 development, but shrink and disappear, their ova being incapable of impregnation. 

 At puberty, the ovaries enlarge, are more vascular, the Graafian vesicles are 

 developed in greater abundance, and their ova capable of fecundation. 



Discharge of the Ovum,. The Graafian vesicles, after gradually approaching the 

 surface of the ovary, burst; the ovum and fluid contents of the vesicles are 

 liberated, and escape on the exterior of the ovary, passing from thence into the 

 Fallopian tube, the fimbriated processes of which are supposed to grasp the ovary, 

 the aperture of the tube being applied to the part corresponding to the matured 

 and bursting vesicle. In the human subject, and most mammalia, the maturation 

 and discharge of ova occur at regular periods only, and are indicated, in the mam- 

 malia, by the phenomena of heat or rut ; and, in the human female, by menstruation. 

 Sexual desire is more intense in females at this period, and, if the union of the 

 sexes takes place, the ovum may be fecundated. 



Corpus Luteum. Immediately after the rupture of a Graafian vesicle, and the 

 escape of its ovum, the vesicle is filled with blood-tinged fluid ; and in a short 

 time the circumference of the vesicle is occupied by a firm, yellow substance, 

 which is probably formed from plasma exuded from its walls. Dr. Lee believes 



