412 



LIFE ON THE EARTH 



ing from the heart -through the arteries and capillaries into 

 the veins and back to the heart. 



As a rule the arteries are below the surface of the body, 

 where they are protected, but if the finger is placed on 



the wrist or the side of 

 the face near the ear, 

 an artery can be felt 

 through which the blood 

 is pulsing. The veins 

 can be seen in the back 

 of the hand and a pin 

 piercing the body any- 

 where will break open 

 some of the capillaries 

 and cause blood to ooze 

 out. The capillaries 

 spread throughout the 

 entire tissue of the body 

 and supply with food 

 and oxygen the different 

 living cells of which the 

 body is composed. 



The heart is a muscu- 

 lar force pump composed 

 of four chambers, two 

 auricles and two ven- 

 tricles. It is shaped 

 somewhat like a pear and is situated almost directly be- 

 hind the breastbone. The blood coming back from the 

 veins flows into the right auricle, a chamber with rather 

 flabby walls. From here, it passes through a valve into 

 the right ventricle, which is a chamber with verv thick 



THE CIRCULATORY SYSTEM 



Notice the veins (white) are nearer the 

 surface than the arteries (black) . 



