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) 



Urachu 



----■■> , 



Mesonephric ducts 



_ Ccelom 



Primitive renal pelvis 



Rectum 



Fig. 362.— I 



302 — I rom a reconstruction of the caudal end of a human embryo 

 of n 5 mm, (4.} weeks). Keibel. 



Umbilical artery 

 Bladder 



r~ 



Symphysis pubis - " — 

 Urogenital sinus^. i 



Genital tubercle '""' 



Arms _— V-4f3 



Tail- 



1 r -> 



•\ ... 



/ 



Broad ligament 

 of uterus 



- Mullerian duct 

 -- Mesonephric duct 

 Ureter 



Recto-uterin 

 excavation 



Rectum 



Fig. 363. — From a reconstruction of the caudal end of a human embryo 



of 25 mm. (8j|-o 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- 



