CLOACA, BLADDER, URETHRA AND UROGENITAL SINUS 



207 



is connected by the constricted portion with (2) the phallic portion of the uro- 

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



Cwlom Rectum 



cphric ducts 



Vesico-urethral anlagi 

 Phallic portion of urogenital stniis 



il etanephros 



Ureter 



Fig. 218. — Reconstruction of the caudal portion of an 11.5 mm. human embryo showing the differen- 

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



sexes and forms a greater part of the urethra (Fig. 219). The vesico-urethral 

 anlage enlarges and forms the bladder and a portion of the urethra. In 7 mm. 



Genital gland 

 Mesonephric fold' 

 Anlage of bladder 



Utero-vaginal anlage. 



Mesonephros 



ff - ■ ' I ' — Ureter 

 // / Miillerian duct 



Mesonephric duct 



Rectum 



Spinal cord 



Anal membrane 



Fig. 219. — Reconstruction of the caudal end of a 29 mm. human embryo showing the complete 

 separation of therectum and urogenital sinus and the relations of the urogenital ducts (after Keibel's 

 model). X 15. 



embryos the proximal ends of the mesonephric ducts are funnel shaped, and 

 at 10 mm., with the enlargement of the bladder, these ends are taken up into 



