340 



THE URINARY SYSTEM 



uniting with their fellows and receiving other arched tubules along 

 their entire course. They then cross the boundary zone of the 

 medulla, and finally, in the papillary zone, form the large terminal 

 tubules, ducts of Bellini, which pour the urinary secretion into 

 the renal calyces. 



Each uriniferous tubule may thus be subdivided into several 

 portions which differ from each other, not only in their location, 



but also in the character 

 of their lining epithelium. 

 The successive portions 

 which compose a single uri- 

 niferous tubule may be enu- 

 merated as follows : 



1. Capsule of the Mal- 

 pighian body. 



2. Neck of the tubule. 



3. Proximal convoluted 

 portion. 



4. Descending limb of 

 Henle's loop. 



5. Loop of Henle. 



6. Ascending limb of 

 Henle's loop. 



7. Distal convoluted 

 portion. 



8. Arched collecting 

 tubule. 



9. Straight collecting 

 tubule. 



10. Duct of Bellini. 



It should be borne in 

 mind that all of these sev- 

 eral portions form only 

 successive parts of a single 

 uriniferous tubule. Those 

 portions of the urine which 

 are secreted into the cap- 

 sule of the Malpighian body 

 must therefore find their 

 way through each of these successive portions before it can reach 

 the excretory passages of the renal calyces, pelvis, and ureter. 



FIG. 280. RECONSTRUCTION OF A URINIFEROUS 



TUBULE OF AN INFANT. 



a, glomeruli ; J, Henle's tubules ; c, distal con- 

 voluted; d, junctional; 0, collecting tubule. 

 (After Stoerk.) 



