402 



TEXT-BOOK OF EMBRYOLOGY. 



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 

 Ccelom 



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 si 



Genital tubercle 

 Urethra 



Ovary 



Broad ligament 

 of uterus 



- Mullerian 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- 



