164 



STRUCTURE OF THE KIDNEY. 



Cavity of 

 Kidney 



capillaries to the tube is peculiar. The inner end of the tube 

 is enlarged into a ball ; this ball is deeply depressed opposite 

 the point where the tube leaves it. Into this depression is 

 fitted a globular tuft of capillaries. The arrangement may be 

 illustrated by the common toy known as the " cup and ball." 

 The handle of the cup should be hollow to represent the tube ; 



the cup should be double- 

 walled, the space between 

 the inner and outer layers 

 continuous with the hollow 

 of the handle. Instead of 

 a solid ball held by one 

 string, there should be a 

 yarn ball with two large 

 strings attached to one 

 side, one representing the 

 artery, the other the 

 vein j the yarn ball 

 represents the dense 

 cluster of capilla- 

 ries. A still better 

 illustration of the urinary 

 tube and capsule may be 

 made thus : Take a thistle tube (used in the chemical labora- 

 tory), let down into the bulb a rubber balloon or bag of sheet- 

 rubber or cloth, fastening the margin around the rim of the 

 bulb; put a little ball of red yarn in the depression ' of the 

 bag hanging in the bulb ; have two ends of the yarn project- 

 ing to represent the artery entering and the vein leaving the 

 capsule. The vein, soon after it emerges, breaks up into 

 another set of capillaries which extend around the tube. A 

 number of these primary tubes unite, and many of the com- 

 mon ducts open at the apex of each of the urinary pyramids, 



Ureter 

 Fig. 53. Cross Section of Kidney. 



