KESPIKATORY OKGANS 



313 



loaded from them. Finally, we traced the source of the 

 oxygen supply to the lungs of the body, and the wastes to 

 the kidneys. The organs which are concerned in the sup- 

 ply of oxygen to the cells and in the removal of the carbon 

 dioxide from the body are spoken of collectively as the 

 respiratory or breathing system. 



Respiratory organs. — The term respiration (re, again, 

 and spiro, I breathe) in- 

 volves two distinct actions. 

 The taking of air into the 

 body is called inspiration, 

 or inhaling. The tlirowing 

 out of the body of carbon 

 dioxide and the air which 

 has been freed of oxygen, 

 is called expiration, or ex- 

 haling. These two pro- 

 cesses of respiration are 

 performed by various kinds 

 of organs in the lower ani- 

 mals, but in man and in all 

 the other vertebrates, ex-, 

 cept the fishes, the principal 

 organs of respiration are the 

 lungs. Coimecting with the 

 lungs, which are located in 

 the thoracic cavity, are 

 several passages and tubes 

 which bear a part in the 

 process and' are to be in- 

 cluded in our term respiratory organs. The relation 

 of these parts to the lungs can be best understood 



Fig. 145 — Kelation of the buccal and 

 nasal cavities to the esophagus ; 7t, 

 brain cavity; Z,hard palate ;/, uvula; 

 g, opening of Eustachian tube to ear; 

 e, epiglottis ; h, tongue ; c, windpipe ; 

 b, esophagus. 



