82 DEVELOPMENT OF EXTERNAL GENITALIA IN THE HUMAN EMBRYO. 



For this reason, the strict usage of these terms would require the continued use of 

 the inclusive term phallus until the separation is culminated. 



The phallus period is thus terminated by the formation of the raph.6 and the 

 scrotum in the male, and the posterior commissure of the labia majora in the 

 female. Thus the definitive characteristics of the external genitalia are organized 

 and the recognition of the sex of the embryos is correspondingly simplified. These 

 observations, in the strict sense, diverge from the statement made by Felix (1912, 

 p. 949) : 



" The beginning of the sexual differentiation can hardly be assigned to a definite period, 

 since it takes place quite gradually and even in advanced stages presents difficulties to 

 diagnosis. We base our diagnosis on the position of the ostium urogenitale relative to 

 the coronary sulcus on the one hand and the anal opening on the other. Male embryos 

 are distinguished by the distal (distal here has reference to the base of the phallus) 

 circumference of the ostium urogenitale always lying in the coronary sulcus, while the 

 proximal circumference becomes more and more distant from the anal opening. Female 

 embryos may be recognized by the urogenital opening retreating away from the coronary 

 sulcus by the gradual closure of its distal part, while its proximal part always lies close 

 to the anal opening; the differentiating moment is, accordingly, both positive and nega- 

 tive in each sex." 



While this statement, if it be interpreted broadly, may to a certain extent be 

 considered as containing the germ of the diagnostic point which I have found to be 

 of value in the early recognition of sex in the human embryo, it plainly does not 

 agree with my own observations, in that Felix limits it to the final period when I 

 find definitive changes taking place in the external genitalia, and at which time the 

 modifications are so characteristic that examination of the external genitalia almost 

 at once enables one to definitely say that one embryo is male and another is female. 

 It must be emphasized, however, that it is still necessary to make careful examina- 

 tion of the genitalia to obtain a correct diagnosis, because from this time throughout 

 the rest of the fetal period individual variations are more pronounced than in the 

 preceding embryonic period. In many of the females, for example, the clitoris 

 attains considerable size, and if this alone is considered, or if only a cursory examina- 

 tion is made, such an embryo might easily be mistaken for a male. (A comparison 

 of figs. 33 and 34, males, with figs. 37 and 46, females, will illustrate this point.) 

 In fact, in the majority of males between the lengths of 50 and 100 mm. CR, 

 the exposed penis seems to be comparatively shorter than the clitoris in females of 

 the same size, an effect which is largely produced by the varying development 

 of the penial-scrotal frenulum. 



So few pronounced morphological changes take place in the developing geni- 

 talia during the rest of the period covered in this study that it will not be necessary 

 to divide them into successive stages. 



Although I have not yet been able to make a complete study of the develop- 

 ment of the prepuce, my observations upon its formation from the external ex- 

 amination of older embryos may be of value and are therefore included in the 

 present account as suggesting the apparent formation of this structure, although 



