150 VITAL FUNCTIONS 



454. Parts concerned in Respiration. The parts con 

 cerned in the respiration of Man may, therefore, be ai- 

 ranged 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 ? 



