OVARY (FUNCTIONS). 



parturition is accomplished by other means. 

 The process by which this is effected has 

 been compared by Blumenbach to the spon- 

 taneous bursting of an abscess. Here the 

 process consists in an increasing accumulation 

 of fluid within, conjoined with a gradual 

 attenuation of some particular part of the 

 containing walls. So many points of simi- 

 larity, indeed, may be traced between these 

 two processes, that the term " inflammation " 

 is employed by some authors in describing 

 the preparatory changes in the Graafian fol- 

 licle. 



The resistance which the ovum and other 

 contents of the vesicle require to overcome 

 before any portion of these can escape con- 

 sists, it must be remembered, in the combined 

 opposition of no less than four membranes, 

 in addition to any portion of the proper 

 ovarian stroma which may intervene. These 

 are, first, the ovisac ; then its capsule, united 

 to the former, and with it constituting the 

 Graafian follicle; thirdly, the tunica albuginea ; 

 and fourthly, the peritoneal covering of the 

 ovary. These four, shortly previous to the 

 rupture, become so intimately united together 

 that it is no longer possible to separate, nor 

 is it easy always to distinguish them from 

 each other, with the exception, however, of 

 the innermost layer, which can generally be 

 more easily traced than any of the rest, on 

 account of its peculiar yellow colour. 



Upon the surface of the most salient por- 

 tion of the projecting follicle (jig. 380. a) the 

 peritoneum, as already stated, may be wanting; 

 the tunica albuginea also beneath has become 

 greatly attenuated, and is sometimes found 

 completely eroded, whilst internally the yellow 

 coat of the follicle is also observed to be 

 thinnest about this spot. Every preparation, 

 therefore, is made for the laceration of the 

 follicle at a given point, the seat of which can 

 also be further determined by the observation 

 that in this place the conjoined membranes, 

 previously highly vascular, have become more 

 transparent, "whilst their vessels, having be- 

 come atrophied by compression, now carry 

 little or no blood. 



A very slight force is now sufficient to 

 produce the rupture of the follicle in this 

 precise spot, and such a force is supplied by 

 the gradual accumulation of fluid, whether 

 albuminous or sanguineous, or both, within 

 the cavity. 



It is believed by Coste that when the ovi- 

 sacs have reached this point, which is the 

 full term of their growth, they may remain 

 stationary until a state of excitement arises, 

 produced partly by the maturity of the ovum, 

 and partly by the approach of the sexes, and 

 that it is under the influence of such an ex- 

 citement that the rupture of the follicle most 

 commonly takes place. What probability 

 there is for such a supposition will be here- 

 after more fully considered. Whether in- 

 fluenced by any external stimulus, or whether 

 occurring spontaneously, and from causes 

 existing within the follicle, the increase of its 

 fluid contents becomes at length so great that 



559 



the cavity is distended beyond measure, and 

 its walls can no longer resist the pressure, 

 but give way at the thinnest and most pro- 

 jecting part. But it is probable that another 

 power comes also into operation to aid this 

 process. The wavy outline which has been 

 already noticed (fig. 381. c) as presented in a 

 slight degree by the still unbroken ovisac, to- 

 gether with a certain amount of thickening of 

 this coat, indicates a growth of this more 

 rapid in proportion than that of the outer 

 layer or tunic of the ovisac. This, therefore, 

 will in some degree add to the pressure, be- 

 cause the outer layer of the follicle not being 

 distensible beyond a certain limit, any in- 

 crease of the contents, whether fluid or solid, 

 will alike contribute to augment the force 

 which is brought to bear upon the weakest 

 point of the walls. 



As soon as the rupture has taken place, 

 and the opening in the coats of the follicle 

 and in the corresponding portion of the ova- 

 rian coverings is sufficiently large to admit of 

 the passage of the ovum, the latter escapes, 

 together with portions of the membrana gra- 

 nulosa. 



On one occasion Pouchet was so fortunate 

 as to meet with an opportunity of observing 

 the ovum as it was in the act of escaping 

 from the ovisac, and was lying between the 

 margins of the lacerated opening. 



Of the five coats which together compose 

 the ovarian and follicular walls, four only, it 

 will be observed, can offer any obstacle to the 

 escape of the ovum; because the membrana 

 granulosa, which is the innermost of all, con- 

 tains rather than covers the ovum, whose 

 escape cannot be impeded, but will be rather 

 assisted by that membrane. Barry explains 

 the mode in which this probably occurs as 

 follows: The ovum, imbedded in the cu; 

 mulus and granular disc which form the centre 

 of the membrana granulosa, at the moment 

 when the laceration occurs, experiences the 

 vis a tergo occasioned by the pressure forward 

 of the fluid, endeavouring to escape from 

 within the follicle. This pressure is increased 

 by the thickening of the inner wall of the 

 follicle, amounting in some instances to an 

 exuberant growth, which will act upon the 

 ovum through the medium of this fluid. The 

 obstacle to the escape of the ovum w hich had 

 up to this moment existed, being removed by 

 the laceration and absorption of the ovarian 

 and follicular walls, that portion of the mem- 

 brana granulosa which lies immediately behind 

 the lacerated coats, where the ovum is im- 

 bedded, presents a surface for the operation 

 of the vis a tergo more or less considerable, 

 according to the extent of the rupture. 



And now the elasticity of the coats of the 

 follicle, together with some pressure from the 

 weight of the parts surrounding its base, 

 come in aid of this force, and complete the 

 expulsion of the ovum, which escapes together 

 with a portion of the membrana granulosa, 

 and passes into the infundibular end of the 

 oviduct. 



Fig. 383. shows the mode in which this pro- 



