200 



THE UROGENITAL SYSTEM 



metanephros is of double origin. The ureter, pelvis, calyces, and collecting 

 tubules are outgrowths of the mesonephric duct. The secretory tubules and the 



IVolJIiiii duel 



Hind-gut 



Oilier zone 

 - [liner zone 

 Pelvis of kidney 

 Bladder 



Cloaca 



Fig. 209. — Reconstruction of the anlages of the metanephros in a human embryo of about 9 mm. 

 (after Schreiner). The layers lettered Inner and Outer zone constitute the nephrogenic tissue of the 

 metanephros. 



capsules of the renal corpuscles are differentiated from the isolated caudal end of 

 the nephrogenic cord and thus have a similar origin as the mesonephric tubules. 



Cranial 

 tubule 



Caudal 

 pole tubide 



Ureter 



Cranial 

 pole tubide 



Central 

 tubide 



Pelvis' 



Caudal 

 tubule 



Ureter' 



Cranial pole tubule 



Ventral central 

 tubule 



Secondary 



collecting 



tubules 



, Tertiary collecting 

 tubule 



Fig. 210.— Diagrams showing the development of the primitive pehis, calyces and collecting tubules 

 of the metanephros (based on reconstructions by Schreiner and Felix). 



In embryos of about 5 mm. the mesonephric duct makes a sharp bend just 

 before it joins the cloaca and it is at the angle of this bend that the ureteric evagi- 



