The Development of the ITj^Tien 



99 



it. It is here very well developed and is composed entirely of vaginal 

 elements. 



The explanation that suggests itself from the study of my sections 

 is similar to Dohrn's ('75). It points to the hymen as of vaginal 

 origin, independent of the place at which the vagina breaks into the 

 urogenital sinus.^ This spot is already clearly to be seen in the 14 cm. 

 fetus as shown in Nagel's illustration (Fig. 9). Within arises a fold 

 of vaginal tissue, the true hymen, stretching almost completely across 

 the vaginal canal. At the point where the vaginal bulbus breaks through, 



Fig. 6. Sagittal section a little to left of median line (Embryo 5). Section 

 No. 191. F., fold; H., hymen; R., ventral wall of rectum; S., sphincter ani 

 muscle ; U., lu-ethra ; Y., vagina. Magnified 5 X. 



the so-called j\Iuellerian eminence, a more or less well marked fold of 

 tissue is left. As the fetus develops this fold becomes obliterated. In 

 cases of arrested development we may have the fold persisting almost to 

 birth, thus giving the picture of a bilamellate or double hymen. 



'In this and subsequent arguments I have assumed that the vagina is 

 entirely formed by the coalesced Muellerian ducts and not to any extent by 

 the sinus urogenitalis. Practically the only testimony that v^^ould speak 

 against this view is the occasional presence of epithelial areas that appear 

 to come from the urogenital sinus. The interpretation of such epithelial 

 areas is, however, a matter of great uncertainty, as has recently been pointed 

 out by Meyer ('07) in a discussion on the remnants of the WolfHan ducts. 



