2o6 



THE UROGENITAL SYSTEM 



Hind-gut 



Htnd-gut 



Mesonephric 

 dud 



•AUanlois 

 'Cloaca 



Cloacal membrane 



AUantois 



Mesonephric duct-^ 

 Metanephros- 



Cloaca- 



Hind-gut Mesonephric 

 duct 

 AUantois 



Metanephros 



Cloacal membrane 



Cloaca 



Tail^gut 



Cloacal membrane 

 Tail-gut 



Fig. 216. — Four stages showing the differentiation of the cloaca into the rectum, urethra and 

 bladder (after reconstructions by Pohlman). X about 50. A, from a human embryo of 3.5 mm.; 

 B, at about 4 mm.; C, at 5 mm.; D, at 7 mm. 



Mesonephric duct 

 Metaneph 



Intestine 



AUantois 



Anlage of bladder 



Cloacal mernbrane 



Ureter' 

 Urogenital sinus' 

 Rectum' 



Fig. 217. — Reconstructions from a 12 mm. human embryo showing the partial subdivision of the cloaca 

 into rectum and urogenital sinus (after Pohlman). X 65, 



