THE EXTERNAL GENITAL ORGANS. 597 



same in all embryos, but from about the tenth week differences 

 become apparent between the two sexes. 



In the male, the genital tubercle elongates, and forms the 

 penis. The lips of the groove, along the posterior surface of the 

 tubercle, meet and fuse to form the canal of the penis, or penial 

 urethra ; and, by a similar fusion of the lips of the urino-genital 

 opening, the penial urethra and urino-genital passage become 

 directly continuous with each other. The glans penis is at first 

 solid, but towards the end of the third month the groove extends 

 forwards along it, and, gradually closing from behind forwards, 

 carries the opening of the urethral canal to the apex of the 

 glans. The prepuce appears, towards the end of the third 



FIG. 252. The external genitalia of a male Human Embryo towards the end 

 of the third month. (From Kolliker, after Ecker.) 



a, anus, f, penis. /, raphe formed by union of lips of genital groove, hi, scrotum. 

 r, vaphe formed by union of the two halves of the scrotum, s, coccyx. 



FIG. 253. The external genitalia of a female Human Embryo towards the 

 end of the third month. (From Kolliker, after Ecker.) 



a, anus. >, clitoris. /, genital groove, ug, urino-genital aperture. M, labia majora. 

 n, labia minora. or inner genital folds, s, coccygeal region. 



month, as a fold of skin round the base of the glans, and is at 

 first interrupted ventrally by the urethral groove. 



The scrotum is formed from a pair of folds of skin, the labio- 

 scrotal or outer genital folds, which arise at the sides of the 

 urino-genital opening, and ultimately unite with each other in 

 the median plane behind the penis (Fig. 252, hi). 



In the female the genital tubercle remains small and becomes 

 the clitoris (Fig. 253, e) ; and the genital groove remains open. 

 The inner genital folds (Fig. 253, w), at the sides of the urino- 

 genital opening, become the labia minora or nymphas ; while the 

 outer genital, or labio-scrotal folds, lit, become the labia majora, 

 and, in front, the mons Veneris. 



