80 DEVELOPMENT OF EXTERNAL GENITALIA IN THE HUMAN EMBRYO. 



tion of an open coronary sulcus demarks the terminal, knob-like glans from the 

 remainder of the phallus. The most significant changes, however, are those in- 

 volved in the separation oi the urogenital opening and anus. These modifications, 

 more extensive in the male than in the female, are brought about by the trans- 

 formation of the open, gutter-like urogenital sinus into the tubular urethra, due to 

 the almost complete fusion of the urethral folds to form the raphe". At the same 

 time the labio-scrotal swellings migrate from their primitive lateral position to 

 a new one caudal to the penis, forming the scrotum. 



An early stage in this series of modifications is shown in figure 24. The 

 ridge-like raphe now separates the anal opening from the proximal end of the 

 lenticular urogenital opening, the distal end of which continues to the tip of the 

 glans as a narrowing slit. Coincident with this fusion of the urethral folds to form 

 the raphe, the labio-scrotal swellings shift slightly, so that their greatest tumidity 

 now lies caudal to the penis instead of lateral to it, as heretofore. 



Regarding the formation of the scrotum, Felix (1912) makes such conflicting 

 statements that it is not at all clear just what his conclusions are. In his prelimi- 

 nary account (p. 953) he states: 



"The basal growth of the pars pelvina must produce a new area, interposed between 

 the base of the penis and the anal opening, and the best name for this is the unpaired 

 scrotal area (fig. 642)." 



The figure referred to by him, according to my interpretation, is that of a 

 female specimen, and the area he labels as the unpaired scrotal area I should de- 

 signate as the posterior commissure. He continues: 



"In embryos of 60 mm. head-foot length this (unpaired scrotal area) becomes raised 

 up in toto and forms the unpaired scrotal swelling, into which the two genital swellings, 

 which we may now term the scrotal swellings, extend from above .... As soon as 

 the descensus is complete this unpaired scrotal area alone forms the scrotal sack, the paired 

 scrotal swellings to the right and left of the penis fading out into the surrounding areas." 



Later, in referring to the development of the labia majora in the female, he 



says (p. 955) : 



"The two genital swellings on this account are not prolonged anally to form an un- 

 paired scrotal tubercle, and consequently they do not fade out as in the male but persist 

 as the labia majora." 



Finally, in his resume* of the development of the external genitalia he con- 

 cludes (p. 958) : 



"In the male the tuberculum genitale fades out in all its parts and in its place there is 

 formed at the anal periphery of the phallus, from the unpaired scrotal area, a new swelling, 

 the unpaired scrotal sack." 



An analysis of the above shows that he has made two statements implying 

 that the labio-scrotal swellings are transformed into the scrotum (in toto or in part), 

 and two other equally emphatic statements implying that they play no part in its 

 formation. Furthermore, if we accept his first statement, it is still doubtful 



