CLOACA, BLADDER, URETHRA AND UROGENITAL SINUS 



207 



Hind-gut 



Hind-gut 

 Mesonephric 

 duct 



Cloacal membrane 



Hind-gut Mesonephric 

 AUantois 



Metanephros 



loacal membrane 



Cloaca 



Tail-gut 



* Cloaca] 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,&i 7 mm. 



Mesonephric duct 

 Metanephros 



Intestine 



Allantois 



A nlage of bladder 



loacal membrane 



FIG. 217. Reconstruction from a 12 mm. human embryo, showing the partial subdivision of 

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



