890 



DEVELOPMENT OF THE EXTERNAL GENITALS. 



perineum, between the uraehus (now become the urinary bladder) (fig. 682, 5, b) and the 



lT*e M ale, the genital eminence enlarges, its groove deepens from the opening of the 

 bladder onwaixls to the apex of the elevation at the 10th week. The two edges unite to enclose 



Fig. 684. 



Development of the external genitals. /. and //.Genital eminence ; r, genital groove ; s, 

 coccyx ; w, cutaneous elevations. IV.-P, penis ; E, raphe penis ; S, scrotum. ///.- 

 r, clitoris ; /, labia minora ; /, labia majora ; a, anus. V. and VI Descent of the 

 testicle ; /, testis ; m, mesorchium ; pv, processus vaginalis of the peritoneum ; M, ab- 

 dominal wall ; S, scrotum. 



the groove which becomes the urethra. When this does not take place, hypospadias occurs. 



At the 4th month the glans, and at the 6th the prepuce, are formed. The large cutaneous 



folds meet in the middle line or raphe to form the scrotum. 



In the female, the undifferentiated condition remains to a certain extent permanent, lhe 



small genital eminence remains as the clitoris, the margins of its furrow become the nymphae, 



the cutaneous elevations remain separate to form the labia majora. The uro-gemtal sinus 



Fig. 685. Fig. 686. Fig. 687. Fig. 688. 



Fig. 685. R, rectum continuous with the allantoi3 (ALL bladder) ; M, duct of Miiller 

 (vagina) ; A, depression of skin below genital eminence, growing inwards to form the 

 vulva. Fig. 686. The depression has become continuous with the rectum and allantois 

 to form the cloaca (CL). Fig. 687. The cloaca is becoming divided into uro-genital 

 sinus (SU) and anus by the downward growth of the perineal septum. The ducts of Miiller 

 are united to form the vagina (V). Fig. 688. Perineum completely formed. 



remains short as the vestibule of the vagina, while in man, by the closing of the genital groove, 

 it has a long additional tube, the urethra. [The accompanying illustrations, after Schroeder, 

 show the changes of the external organs of generation in the female. In the early period (6th 

 week), the hind-gut (fig. 685, R), allantois (ALL), and the Miillerian ducts (M) communicate, 

 but not with the exterior. About the 10th week a depression or inflection of the skin takes 

 place, genital cleft, until it meets the hind-gut and allantois, whereby the cloaca (fig. 686, CL) 

 is formed. The cloaca is then divided into an anterior part, the uro-genital sinus, into which 

 the Miillerian ducts open, and a posterior part, the anus. There is a downward growth of the 

 tissue between the hind-gut and the allantois to form the perineum (fig. 687). The uro-genital 

 sinus then contracts at its upper part to form the short urethra, its lower part remaining as the 

 vestibule (fig. 688, SV), while the vagina has been formed by the union of the lower parts of 

 the two Miillerian ducts. The bladder (B) is the expanded lower end of the stalk of the 

 allantois.] 



The causes of the difference of sex are by no means well known. From a statistical analysis 

 of 80,000 cases, the influence of the age of the parents has been shown by Hofacker and 



