CLOACA, BLADDER, URETHRA AND UROGENITAL SINUS 



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

 7 mm. 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 



Allantois 



Rectum 



Mesonephric duch 



Vesico-urethral 

 anlage 



Phallic portion 

 of uroyenifal sinus 



.Metanephros 



Ureter 



'mwrnaBa***^'* *^*&* 



FIG. 211. Reconstruction of the caudal portion of an 11.5 mm. embryo showing the differentiation of 

 the rectum, bladder and urethra (Keibel). 



Genital gland 

 Mesonephric fold 

 /Inlaqe. of bladde, 



(Jte.ro-vag'ina[ anlage 



Phallic urethra. 

 Cloacal membrane 



Mesonephrvs 

 Mesonephric duet 



Urekr 

 Muellerian duct 



-Mff.fi 



-Mesonephric due}" 

 ftecfum 



Spinal card 



Rectum 



FlG. 212. Reconstruction of the caudal end of a 25 mm. embryo showing the complete separation of the 

 rectum and urogenital sinus and the relations of the urogenital ducts (after Keibel's model). 



its wall until the ureters and mesonephric ducts acquire separate openings. [The 

 ureters, having previously shifted their openings into the mesonephric ducts from 

 a dorsal to lateral position, now open into the vesico-urethral anlage lateral to 

 the mesonephric ducts. The lateral walls of the bladder anlage grow more rap- 



