THE RESPIRATION 



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 pusJi air through 

 tJie windpipe into tfie 

 lu tigs a n d exp and 

 tli cm (Ex p. 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 ?//. The ribs 

 are also drawn 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 itpper 

 chest. Effects of confining the 

 waist. 



i . There are two pairs of - 



FIG. 76. BLACKBOARD SKETCH, to 

 show how the chest is expanded when 

 the ribs move upward and outward. 



ribs below, while there are none 



