THE PLAOENTATION OF PERAMELES. 429 



raeles led to a re-investigatioiij by means of serial sections of 

 the structure of the female genital organs, especially with 

 reference to the question of the existence or otherwise of such 

 a median pseudo-vaginal passage in virginal and non-gravid 

 genital organs. The results of this investigation will be set 

 forth in detail elsewhere. Suffice it here to state that in the 

 virginal genital organs the two uteri do not open into each 

 other posteriorly, and there is no trace of a median vaginal 

 passage or of any epithelial or other track, which might indicate 

 the site of a future passage of any kind whatever. 



In the non-gravid organs of animals with large pouch-young, 

 on the other hand, the median pseudo-vaginal cleft is found to 

 exist, but it neither stands in open communication with the 

 common uterine canal nor does it open into the cloaca. As in 

 the post-partura stage, the passage is wholly destitute of 

 any epithelial lining or any other specialised wall. 



As to the mode of formation of this median passage in the 

 first instance I am unable to come to any definite conclusion. 

 It has just been stated that in the virgin the uteri do not com- 

 municate with each other posteriorly, and no median passage 

 exists. The latter is, then, evidently formed either just before 

 or at the first act of parturition. That the embryo should in its 

 passage out literally bore its way through the connective tissue 

 seems to me improbable, but at least it would seem as if the 

 hindrance to the exit of the foetus offered by the narrow openiuo- 

 of the uterus into the lateral vaginal canals was actually 

 greater than the resistent power of the tissue between the 

 posterior ends of the uteri, and that rupture of the latter must 

 occur. That some such rupture does occur is evidenced not 

 only by the appearance of the false passage, but also by the 

 pretty extensive extravasations of blood found both in and 

 surrounding the track followed by the foetus during its eo-ress 

 i. e. the median pseudo-vaginal passage. 



It is evident that the detailed character of the phenomena 

 of parturition, and above all the nature of the causes producing 

 the extraordinary condition above described, can only be 

 definitely ascertained by the examination of the genital organs 



