154 VITAL FUNCTIONS. 



Parts concerned in Respiration. The parts concern- 

 ed in the respiration of Man may therefore be arranged 

 into three divisions : First, the bones which form the 

 respiratory cavity ; second, the muscles by which these 

 bones are moved; and third, the respiratory organs 

 themselves. 



Belonging to the first division, there are one sternum, 

 twelve pieces of the spine, called the dorsal vertebra, 

 and twenty-four ribs. 



The second division consists of the diaphragm, and 

 several pairs of muscles. 



The third division contains the trachea, bronchia, and 

 lungs. 



There is no necessity of describing the skeleton of 

 the trunk, having already done so for another purpose, 

 under figures 63, 64, and 65. 



The muscles concerned in respiration are the dia- 

 phragm, and the intercostal muscles, together with several 



What is the principal organ concerned in respiration 1 



