SECRETION. 



437 



The capsule surrounds a small, red, spherical body known as the 

 glomerulus, or Malpighian corpuscle, after Malpighi, its discoverer. 

 The capsule, about one one-hundredth of an inch in diameter, is con- 

 stricted at its neck to form a tube. Beyond this constriction the 

 tube pursues a very convoluted course through a considerable extent 

 of the cortical area, as the tubulus contortus, which is about one six- 

 hundredth of an inch in diameter. Soon the convolutions disap- 

 pear to give place to a more or less spiral tube as it approaches the 

 medulla: spiral tube of Schachowa. 



Fig. 165. Longitudinal Section of a Malpighian Pyramid. (LANDOIS.) 



h, Cortex, i, Boundary or marginal zone, fc, Papillary zone. PF, Pyra- 

 mids of Ferrein. RA, Branch of renal artery. RV, Lumen of renal vein 

 receiving an interlobular vein. TR, Vasa recta. PA, Apex of renal papilla. 

 6, 6, Embrace the bases of the renal lobules. 



At the boundary-line between cortex and medulla the tube 

 becomes suddenly smaller and is now perfectly straight, forming 

 the descending limb of Henle's loop, dipping down for a considerable 

 distance into the pyramid. By the sudden changing of its course 

 backward, but still parallel with its original course, there is formed 

 the loop of Henle, which, continued upward to the cortex, constitutes 

 the ascending limb of Henle's loop. Ascending into the cortex it 



