72 



DEVELOPMENT OF EXTERNAL GENITALIA IN THE HUMAN EMBRYO. 



which show the shorter urethral groove that I have found to be characteristic of 

 female embryos, no special description is given ot these structures. In fact, he 

 realized that for the investigation of the development of the external genitalia a 

 large series of embryos was necessary, and this portion of his paper is for the most 

 part devoted to a plea to his colleagues for more specimens. 



While I realize that I have been more fortunate than any of my predecessors 

 in having at my disposal a larger and more complete series of embryos, I still would 

 reiterate Keibel's plea for more material; because it seems that the more specimens 

 one has at his disposal, the more one realizes the need of additional material in order 

 to study some of the points concerning which there is still a conflict of opinion. 



In 1904 Herzog pointed out that the direction of the phallus made it possible 

 to recognize the sex of an embryro at about the beginning of the third month, in- 

 stead of towards its close. This difference in direction he showed to consist in a 

 greater caudal decurvation of the female phallus, while that of the male remained 

 more nearly at right angles to the axis of the body. His series consisted of 16 

 embryos, varying in length from 20 to 190 mm. Of these, he figures the external 

 genitalia of only 9, none of which bring out very clearly his point of directional dif- 

 ference of the phallus. Some excellent figures of the external genitalia are given by 

 Otis (1906), although the discussion of the genitalia does not form a logical part of 

 his paper. 



CLANS AREA 

 EPITHELIAL TAG 

 LATERAL BUTTRESS 



ANAL PIT 

 ANAL TUBERCLES 



CLUTEAL FOLD 



TEXT-FIGURE 1. Drawing of external genitalia of an embryo 16.8 mm. long (Specimen No. 492), 

 illustrating the genital-tubercle period. X 25. 



From 1890 to 1907 a number of valuable contributions upon the development 

 of the urogenital system in mammalia, especially the domesticated forms, made 

 their appearance. While a number of these (notably the series of investigations 

 carried out by Fleischmann and his pupils) pertained more or less to the develop- 

 ment of the external genitalia, they have proved of but little use in the present 

 investigation, since these papers failed to bring out any early sex differences in the 

 forms studied. 



Felix (1912) gave an exhaustive summary of the accumulated observations 

 upon the development of the human urogenital system, although his discussion of 



