THE DEVELOPMENT OF THE UROGENITAL SYSTEM. 



405 



The narrow part of the sinus is gradually taken up into the wider, resulting in 

 the formation of a sort of vestibule. In both sexes the urethra opens into the 

 deeper end of the vestibule. In the male the mesonephric (seminiferous) 



Cloaca 

 (undivided portion) 



Cloacal membrane ~ 



Tail 



Mesonephric ducts 



_ Coelom 



Primitive renal pelvis 



Rectum 



FIG. 362. From a reconstruction of the caudal end of a human embryo 

 of 11.5 mm. (4^ weeks). Keibel. 



Umbilical artery 

 Bladder 



Symphysis pubis 



Urogenital sinus 



Genital tubercle 

 Urethra 



/-> 

 Ovary 



. Broad ligament 

 of uterus 



Miillerian duct 



Mesonephric duct 

 Ureter 



Recto-uterine 

 excavation 



Rectum 



Tail 



FIG. 363. From a reconstruction of the caudal end of a human embryo 



of 25 mm. (8^-9 weeks). Keibel. 

 The asterisk (*) indicates the urorectal fold. 



ducts open near the external orifice. In the female the opening of the develop- 

 ing vagina is situated on the dorsal side near the external orifice. 



The epithelium of the prostate gland is derived by evagination from the proxi- 



