DEVELOPMENT OF EXTERNAL GENITALIA IN THE HUMAN EMBRYO. 83 



the final corroboration of this will have to be left for future investigation. For 

 this reason, it seems inadvisable at this time to enter into any comparison of the 

 various explanations that have been made to account for its origin. 



After the separation of the phallus into shaft and glans by the formation of a 

 coronary sulcus, the glans remains as a naked, knob-like termination of the shaft 

 (in both sexes) until the embryo reaches a length of about 65 mm. CR. In males 

 of this size the first traces of the prepuce may be noted. The skin of the shaft 

 becomes elevated into a pair of conspicuous rolls on either side of the urethral 

 opening (fig. 41). Gradually these rolls join on the dorsal side of the shaft (fig. 42) 

 to form a flat ridge whose distal margin has grown out to cover the proximal edge 

 (corona) of the glans (embryos 75 mm. CR). The continued outgrowth of this 

 fold results in the gradual inclosure of the glans (figs. 47 to 50) until (embryos 98 to 

 100 mm. CR) the glans is completely covered by the prepuce. 



Accompanying the development of the prepuce, there is a gradual shifting of 

 the urethral opening until (in embryos 85 to 90 mm. CR) it occupies a subterminal 

 position in the frenular notch of the glans. With the completion of the prepuce 

 this primary opening is entirely closed. Some time later a new (the secondary or 

 definitive) terminal urethral opening is formed near the tip of the glans. 



But few important changes take place in the female genitalia in this later period 

 (50 to 100 mm. CR length), these being mainly concerned with the continued 

 growth of the labia majora and the beginnings of prepuce formation. The labia 

 majora increase somewhat in height, so that the inclosed structures become more 

 submerged in the rim which they form, although this submergence is by no 

 means completed at this period. 



The formation of the prepuce is considerably more involved than in the male 

 and all of the folds included in its complete development do not make their appear- 

 ance until some time after the close of the period under consideration. The only 

 observations made are concerned with the glandular portion. This fold apparently 

 develops in much the same way as it does in the male, although it has not been 

 studied as closely and is not as well shown in the figures. Its growth is by no means 

 as rapid as in the male, with the result that the glans of the clitoris is not completely 

 covered by it at the close of this period (100 mm. CR). As has already been noted, 

 the complete separation between the clitoris proper and the labia minora does not 

 take place until considerably later. 



