THE URINE 



3*7 



the latter is continued from the capsule, taking a course of extra- 

 ordinary complexity in order to reach the pelvis of the kidney ; 

 further, the cells found in the tubule are no longer the flat 

 polygonal cells of the capsule, but a something special to the 

 tubule, and even to different parts of it (Fig. 95). 



If the course of a uriniferous tubule is briefly followed (Fig. 96), 

 it is found that on leaving the capsule it becomes twisted in the 

 cortex forming the convoluted tube ; it then forms a spiral tube, 

 and leaving the cortex, runs straight into the medulla, forming 



Fig. 95. — From a Vertical Section of the Dog's Kidney, to show the 

 Structure of the Different Portions of the Renal Tubule (Klein). 



a, Bowman's capsule enclosing glomerulus ; n, neck of capsule ; c c, convoluted 

 tubes cut in various directions ; b, from zigzag tubule ; d, from collecting 

 tubule ; e e, from spiral tubules ;/, narrow part of Henle's loop tubule. In b, 

 c, and e, * rodded ' epithelium is seen (Stewart). 



the descending limb of Henle ; it now makes a sharp turn, the 

 loop of Henle, and travels back to the cortex, in the same way 

 that it left, by the ascending limb of Henle. The descending 

 limb is straight and narrow, the ascending limb is wavy in char- 

 acter and larger. Having reached the cortex, the ascending 

 limb becomes distinctly wider and twisted, forming the zigzag 

 or irregular tubule ; from this a tubule is continued which re- 

 sembles in its contortions the first convoluted portion ; it is 

 termed the second convoluted tubule. This now leaves the cortex 

 and enters the medulla as a straight tube, known as the collecting 



