HOW WE BREATHE 



In tranquil breathing the inspiration of air is effected chiefly 

 by the diaphragm in men, while in forced inspiration the inter- 

 costals play a very important part. In 

 women the diaphragm does not play 

 so important a part as the ribs. 



As the ribs are raised during inspi- 

 ration, the sternum will of course rise 

 with them. This movement may be 

 noticed by laying the hand on the 

 front of the chest while taking a deep 

 inspiration. Again, when the dia- 

 phragm moves, the organs of the abdo- 

 men must follow its movements, and 

 this causes a visible motion of the 

 walls of the abdomen. Hence respi- 

 ration which is effected chiefly by 

 the diaphragm is often termed abdo- 

 minal respiration, while that pro- 

 duced chiefly by movements of the 



Fig. 137. 



side walls of the chest is called costal respiration. 



After the lungs have been inflated by the inspired air they 

 are stretched considerably, and their elasticity is sufficient in 



Fig. 138. Illustrating the 

 Action of the Internal Inter- 

 costals. 



Fig- 139- Illustrating the 

 Action of the External Inter- 

 cost als. 



quiet breathing to expel the air without the aid of any muscles. 

 But in a forced expiration the internal intercostals are brought 



