162 



OUR BODIES AND HOW WE LIVE 



The windpipe is a tube about four inches long, which 

 is protected on the front and sides by stout rings of 

 cartilage. But for these rings the windpipe would close 

 with the slightest pressure and cut off our breath. 





FIG. 100. Relative Position of the Lungs, the Heart, and Some of 

 the Great Vessels belonging to the Latter. 



A, left ventricla ; B, right ventricle ; C, left auricle ; D, right auricle ; E, superior 

 vena cava ; f, pulmonary artery ; G, aorta ; //, arch of the aorta ; K, innomi- 

 nate artery ; L, right common carotid artery ; Af, right subclavian artery ; 

 N, thyroid cartilage forming upper portion of the larynx ; O, trachea. 



The top of the windpipe is protected by a trapdoor 

 known as the epiglottis. This little door, as we have learned, 

 shuts tight when food is swallowed, and keeps the food out 

 of the air passages ; otherwise the food would go the wrong 

 way, and cut short our breath (Sec. 153 and Fig, 69). 



