CHAPTER V. 



THE RELATION OF CYEMIC TO CHORIONIC SIZE. 



The occurrence of hydramnios indicates that in some specimens the relation 

 of cyemic to chorionic size must vary considerably for this reason alone. This 

 could fail to be the case only if hydramnios could be recognized in its beginning, 

 so that such specimens could be excluded. Moreover, since we are as yet 

 unable to recognize the earliest regressive changes in the cyema, this fact too would 

 increase the range of variation in specimens which might be regarded as normal, 

 at present. If we consider specimens classed as pathologic in the Carnegie Col- 

 lection, the disproportion between cyemic and chorionic size would of course be 

 very much greater. This variation, in fact, is over 800 per cent. Since the cyema 

 may be extremely abortive and evidently also disappear entirely, disproportion 

 between cyemic and chorionic dimensions might be extremely great in these speci- 

 mens also. But even aside from these considerations, the relation between chori- 

 onic and cyemic size can not be constant throughout gestation unless the shape of 

 the conceptus were invariable. But we know that such is not the case, for the 

 greater growth in length of the fetus, placental development, the formation of 

 the chorion lave, and other matters, all tend to change the form of the conceptus. 

 It is true that regression of the villi in the region of the chorion Iseve would be 

 compensated for to some extent by placental formation on the other side of the 

 vesicle, but in such large specimens the extrauterine change in form will be con- 

 siderable and thus increase the fluctuation in the measurements. However, it is 

 very probable that the closest correlation exists between cyemic and chorionic 

 size, during the early stages of development, when the conceptus probably is still 

 more nearly spherical. During this time the conceptus also undergoes but little 

 change in form during measurement under proper extrauterine conditions; but 

 even at this time the villi always will be a decidedly variable factor in all external 

 measurements of the chorionic vesicle. Hence it would seem that satisfactory 

 results for a comparison of chorionic and cyemic dimensions probably can not be 

 obtained without taking those of the chorionic vesicle regardless of the villi. Such 

 measurements, however, can not be made accurately without bisecting the vesicle. 



I do not know whether the increase in amniotic fluid is very constant or not, 

 but if its volume changes disproportionately, even if not independently of the 

 length of the cyema, this fact would introduce another variable and so further 

 obscure the real correlation in size between the cyema and its chorionic vesicle. 

 In addition to all these things, there are, of course, the normal variations in growth 

 and the changes in form effected during parturition and fixation, for very few 

 abortuses are obtained and measured when fresh. Besides, the vesicle and the 

 cyema no doubt vary independently of each other in growth, so that a very broad 

 basis becomes necessary before a reliable comparison between the two can be 

 made. For all these reasons, then, it would seem that the volume, or, better still, 



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