CHAPTER XVIII. 



RESPIRATION. 





1. BY Respiration, is meant/the process of taking air into 

 the lungs and throwing it out again. Inspiration is the act 

 of drawing the air in ; expiration, that of forcing it out. 

 Respiration is essential to all animal existence. It is in the 

 lungs that the last change is produced in the assimilation of 

 the food, by which it is converted into that vital fluid, which 

 carries life, and strength, and nourishment to every fibre in 

 the animal system. 



2. The parts concerned in respiration may be arranged 

 into three divisions, viz., 1, the bones which form the respir- 

 atory cavity ; 2, the muscles by which these bones are moved, 



Thorax, or chest; a, the sternum ; b, b, the spine ; c, c, the ribs, 



