DEVELOPMENT OF EXTERNAL GENITALIA IN THE HUMAN EMBRYO. 87 



In female embryos of 60 to 100 mm. CR length there is shown a partial develop- 

 ment of the prepuce, although the complicated set of folds involved in its complete 

 formation is not produced at this time and only partial growth of the glandular 

 portion is completed at the close of this period. While the glandular prepuce is 

 apparently formed in much the same way as it is in the male, its growth is markedly 

 slower, and in embryos 100 mm. long the glans is not completely surrounded by it. 



In these older embryos (60 to 100 mm. CR length) there is also some increase 

 in the height of the labia majora, so that the inclosed portions are somewhat 

 submerged in the rim thus formed, although this submergence is by no means as 

 complete as it becomes in later fetal life. It should also be noted that in fetuses up 

 to 100 mm. CR the labia majora are still cranially separated and there is no indi- 

 cation that they play any part in the formation of the mons veneris. 



CONCLUSIONS. 



1 . There is a morphological sex difference in the external genitalia of the human 

 embryo practically from their first appearance, characterized by marked difference 

 in the length of the urethral groove upon the caudal slope of the genital tubercle. 

 In some embryos the distal end of the groove extends onto the glans region (males), 

 while in others it does not reach to this region (females) . 



2. This should prove to be a fairly reliable character for the recognition of sex 

 in human embryos at an earlier period than has heretofore been possible. 



3. From the first appearance of the genital tubercle, there apparently is no 

 indifferent or undifferentiated period in the development of the external genitalia 

 before they acquire their definite male or female characteristics. 



4. The caudal decurvation of the female phallus, first pointed out by Herzog, 

 is a valid diagnostic characteristic and is applicable at an earlier period than was 

 first indicated. 



5. The phallus period is definitely terminated in both sexes by the assumption 

 of approximately the adult form of the genitalia. In the male this is brought 

 about by the fusion of the urethral folds into the raphe" and the accompanying caudal 

 migration of the labio-scrotal swellings to form the scrotum. In the female it is 

 characterized by the fusion of the caudal ends of the labio-scrotal swellings to form 

 the posterior commissure. 



