256 



STRUCTURE OF THE VERTEBRATES 



evagination arises on either side and grows anteriorly toward 

 the developing metanephros. The anterior end of each outpocket- 

 ing enlarges and branches. Due to continued division the tubes 

 become smaller and greatly multiplied until the terminal 

 branches become the collecting tubules. These grow^ into and 

 are surrounded by the nephric tissues. The tubules of the renal 

 corpuscles have been developing synchronously, each renal 



raining 

 tubule 



'Boivman's capsule 

 ■ -Loop of Henle 



A. Single Tubule 



Cortex- 

 Medulla 



Entrance 

 of Ureter 



B. Gross Anatomy of 

 Urinary Organs 



Fig. 143. Structure of the Kidney. (A) A single tubule with the branching 

 collecting tubule. (B) The gross anatomy of the kidney and bladder in long 



section. 



tubule developing from a small vesicle which invaginates at one 

 end to form a Bowman's capsule, and elongates at its other end 

 to form a kidney tubule. The tubules from the Bowman's cap- 

 sules unite with the collecting tubules, and the connection is 

 completed. 



The amniote kidney is therefore composed of an outer cortex 

 from the nephrotome, and an inner medulla which arises from 

 the branching ureter. The collecting tubules join to form larger 

 tubes, and these empty into the pelvis of the kidney. The latter 



