EXCRETION 



197 



a single tubule are therefore the problems of the kidney as a 

 whole. These structures are all exactly alike. The descrip- 



FIG. 9. THE UPPER END OF THE LEFT KIDNEY, VERTICALLY DIVIDED, AND MAGNIFIED. 



It is invested by a capsule with which, at the hilus, the dilated end of the ureter blends. A 

 portion of a papilla (the end of a pyramid) is shown projecting into one of the calices into 

 which the ureter dilates. The peripheral portion of the kidney containing glomeruli and 

 contorted tubes is termed its cortex, the central portion medulla. At A is shown a single 

 urinary tubule. Commencing at the third glomerulus, it winds in the cortex, descends 

 into the medulla, turns in a loop of Henle, again winds in the cortex, and ends in a collecting 

 tube, which joins a duct. The arrangement of the bloodvessels is shown at B. A straight 

 artery and a straight vein lie side by side. The artery gives branches to the glomeruli. 

 The venules from the glomeruli again divide into capillaries, which supply the contorted 

 tubes and loops of Henle. The ducts are supplied by long arterial capillaries. C shows 

 the structure (magnified) of a glomerular tuft of capillary vessels, invested by a capsule 

 which closes into a contorted tube, at ; dH, a descending limb ; aH, an ascending limb 

 of a loop of Henle ; d, a duct. 



tion of any one of them applies to all. Each begins as a 

 capsule containing a glomerulus. The wall of the bulb which 



