ANIMALS. 137 



smaller, until they become a multitude of minute tubes, 

 called capillaries, passing through every part of the body. 

 At length these again gradually unite in veins (v, ^', v), 

 through which the blood is returned to the heart. It is 



Arteries, Capillaries, and Veins. 



then sent out through another set of tubes, which con- 

 duct it through the lungs, where it is brought in con- 

 tact with the air taken into the luno-s in breathins:, 

 becomes purified, returns to the heart, and starts again 

 on its orij»;inal course. 



