208 



THE UROGENITAL SYSTEM 



sinus (Figs. 217 and 218). The latter extends into the phallus of both 

 sexes and forms a greater part of the urethra (Fig. 219); its fate is described 

 on p. 226 in connection with the external genitalia. 



Ccelom 



Rectum 



Allantois 



Vesico-urethral anlage 

 Phallic portion of urogenital sinus 



'esonephric ducts 



Metanephros 



Ureter 



FIG. 218. Reconstruction of the caudal portion of an 11.5 mm. human embryo, showing the 

 differentiation of the rectum, bladder and urethra (after Keibel's model). X 25. 



Genital gland 

 M esonephric fold' 

 Anlage of bladder. 



Utero-vaginal anlage 



Phallic urethra 

 Anal membrane 



Mesonephros 

 Ureter 



Miillerian duct 



rr-M esonephric duct 



Rectum 



Spinal cord 



Anal membrane 



FIG. 219. Reconstruction of the caudal end of a 29 mm. human embryo, showing the 

 complete separation of the rectum and urogenital sinus and the relations of the urogenital ducts 

 (after Keibel's model). X 15. 



The vesico-urethral anlage enlarges and forms the bladder and a por- 

 tion of the urethra. In 7 mm. embryos the proximal ends of the meso- 

 nephric ducts are funnel shaped, and, at 10 mm., with the enlargement of 

 the bladder, these ends are taken up into its wall until the ureters and meso- 



