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HAND-BOOK OF PHYSIOLOGY. 



plates. This capsule is the dilated extremity of the uriniferous tubule, 

 and contains within it a glomerulus of convoluted capillary blood-vessels 

 supported by connective tissue, and covered by flattened epithelial plates. 

 The glomerulus is connected with an efferent and an afferent vessel. (2) 

 The constricted neck of the capsule (Fig. 240, 2), lined in a similar man- 

 ner, connects it with (3) The Proximal convoluted tubule, which forms 

 several distinct curves and is lined with short columnar cells, which vary 

 somewhat in size. The tube next passes almost vertically downward, 

 forming (4) The Spiral tubule, which is of much the same diameter, and 



FIG. 241. From a vertical section through the kidney of a dog the capsule of which is supposed 

 to be on the right, a. The capillaries of the Malpighian corpuscle viz., the glomerulus, are arranged 

 in lobules; n, neck of capsule; c, convoluted tubes cut in various directions: 6, irregular tubule; d, e, 

 and /, are straight tubes running toward capsules forming a so-called medullary ray; d, collecting 

 tube; e, spiral tube; /, narrow section of ascending limb. X 380. (Klein and Noble Smith.) 



is lined in the same way as the convoluted portion. So far the tube has 

 been contained in the cortex of the kidney, it now passes vertically down- 

 ward through the most external part (boundary layer) of the Malpighian 

 pyramid into the more internal part (papillary layer), where it curves up 

 sharply, forming altogether the ( 5 and 6) Loop of Henle, which is a very 

 narrow tube lined with flattened nucleated cells. Passing vertically up- 

 ward just as the tube reaches the boundary layer (7) it suddenly enlarges 

 and becomes lined with polyhedral cells. (8) About midway in the boun- 

 dary layer the tube again narrows, forming the ascending spiral of 

 Henle's loop, but is still lined with polyhedral cells. At the point where 

 the tube enters the cortex (9) the ascending limb narrows, but the diame- 



