THE RESPIRATION 



79 



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 ngs and exp and 

 them (Exp. 19). 



FIG. 75. FRAMEWORK OF CHEST. 



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 itp. The ribs 

 are also draivn down 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 



FIG. 76. BLACKBOARD SKETCH, to waist. 



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



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



