2IO 



UROGENITAL SYSTEM 



ing tubules, on the other hand, extend out into the cortex as the cortical rays 

 or pars radiata of the cortex. In these rays and in the medulla of the kidney 

 the collecting tubules run parallel and converge to the papillae. 



DIFFERENTIATION OF THE NEPHROGENIC TISSUE 

 In stages from 13 to 19 mm. the nephrogenic tissue about the ends of the 

 collecting tubules condenses into spherical masses which lie in the angles between 

 the buds of new collecting tubules and their parent stems (Fig. 205). One such 



Fig. 205. — Semidiagrammatic figures of the anlage and differentiation of renal vesicles and early 

 developmental stages of uriniferous tubules of mammals, i and 2, anlage and successive stages in the 

 differentiation of renal vesicles, as seen in sagittal sections; 3, section and outer form of tubular anlage 

 before union with collecting tubule at the beginning of S-shaped stage; 4 and 5, successive stages in the 

 development of the tubules, Bowman's capsule and glomerulus beginning with a tubular anlage showing 

 a well developed S-shape (Huber). 



metanephric sphere is formed for each new tubule. The spheres are converted 

 into vesicles with eccentrically placed lumina. The vesicle elongates, its thicker 

 outer wall forming an S-shaped tubule which unites with a collecting tubule, 



