350 



A YEAR IN SCIENCE 



U 



Fig. 164. Experiment 

 to illustrate the effect 

 upon the lungs of the 

 movements of the dia- 

 phragm. The belljar cor- 

 responds to the walls of 

 the thorax ; the rubber 

 balloon to the lungs ; the 

 glass tube to the trachea ; 

 and the sheet of rubber 

 tied over the bottom of 

 the belljar to the dia- 

 phragm. As the dia- 

 phragm is lowered air 

 flows down the tube and 

 inflates jthe balloon. 



together with the elasticity of 

 their walls, is sufficient to force 

 out about one pint of air. 



The chest is enlarged by the 

 movements of the diaphragm 

 and of the ribs. Muscles in the 

 diaphragm cause it to lower. 

 As a result, what happens to 

 the abdomen f Muscles between 

 the ribs, and between the ribs 

 and shoulders, pull the ribs up 

 and this movement pushes the 

 breast bone forward. These 

 movements are controlled by 

 nerves. With effort we can 

 increase their extent and so 

 inhale more air, and W3 can 



B B 



nr 



Fig. 165. Experiment showing movements of ribs in breathing; 

 AB, vertebral column ; CD, and EF, ribs ; DF } breast bone ; a, b, 

 external and internal intercostal muscles ; c, neck muscles. If 

 these muscles contract, the ribs and breast bone are drawn upward. 

 This movement widens the thorax from front to back and from 

 side to side. . 



also forcibly exhale more than the usual amount of air. 

 It is impossible, however, to empty the lungs. The 



