THE RESPIRATION 



79 





Fig. 75. — Framework of Chest. 



atmosphere has a 



height of many miles, 



and the air above is 



pressing on that be- 

 low. When the chest 



walls are raised there 



would be an empty 



space or vacuum be- 

 tween these walls and 



the lungs, did not the 



pressure of the outside 



air push air through 



the windpipe into the 



lu 11 gs and exp a n d 



them (Exp. 19). 



Expiration. — In very active breathing the abdominal 



walls actively contract so 

 that they press strongly 

 upon the digestive organs, 

 which in turn press the 

 diaphragm up. The ribs 

 are also drawn dozen and 

 in. Thus the chest be- 

 comes smaller and forces 

 the air to flow out through 

 the windpipe (Exps. 20 

 and 21). 



Thought Questions. — Why 

 breathing with the waist is easier 

 than breathing with the upper 

 chest. Effects of confining the 



EIg. 76. — Blackboard Sketch, to waist. 



show how the chest is expanded when I . There are two pairs ot 



the ribs move upward and outward. ribs below, while there are none 



