PATHOLOGY OF THE BLADDER AND URETER, 383 



excellent and the only one possible for the knowledge of the 

 time then. 



Another explanation is that of Durand, based on Tourneux's 

 work. It is discussed by Ballantyne in his paper on so-called 

 epispadias in women, and seems to me inadequate. A similar 

 theory is advanced by Shattock. 



The best explanation of extroversion is afforded by the facts 

 now known as to bladder development and the cloacal mem- 

 brane. The bladder in the human female is not developed from 

 allantois except at its apex, but is derived along with the 

 urinogenital sinus from the anterior division of the entodermal 

 cloaca. This cloaca has the cloacal membrane as its anterior 

 boundary, and as this boundary has no mesoderm at one period, 

 it may yield or cleave. This yielding, if complete, necessarily 

 exposes all that is derived from the anterior primitive gut 

 division — viz., bladder, urinogenital sinus, lower third of vagina 

 as in Champneys' case. Less degrees of fissure in linear extent 

 or depth, give the other lesions. These are therefore explained, 

 as Keibel has so well shown, by the actual development of 

 the parts plus some bursting or dilating cause which, if it does 

 occur (and of that we have as yet no proof), must do so at an 

 early period of embryonic life. 



We might also regard extroversion as a persistent blastopore, 

 and for this view a good deal can be said both for and against. 



My own special points have been (1) the identification of the 

 posterior end of the cloacal membrane in the embryo with a 

 point in front of the anus in the adult, and (2) the proof that 

 in certain cases (Champneys' and Opitz') the lesion is formed 

 prior to the complete formation of the vagina, and we thus see 

 its component parts — viz., upper two-thirds Miillerian, and lower 

 third, urinogenital sinus with Wolffian ducts. In adult cases 

 this differentiation is not seen, as the vagina is usually 

 developed normally. 



II. On Apparent Low Implantation of the Ureteric 



Opening. 



A few remarkable cases have been recorded where incontin- 

 ence of urine in the human female has been due to what 



