164 



Life and Health 



These divide into smaller tubes, which continue subdividing 



till the whole lung is penetrated by their minute branches. 



The walls of the larger bronchial tubes would readily 



collapse and close the passage for air, but for a wise 



FIG. 85. Relative Position of the Lungs, Heart, and its Great Vessels. 



A, left ventricle ; B, right ventricle; C, left auricle ; Z>, right auricle ; E, superior 

 vena cava ; F, pulmonary artery ; G, aorta ; //, arch of the~aorta ; fC, innomi- 

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

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



precaution. The horseshoe-shaped rings of cartilage in the 

 trachea and plates of cartilage in the bronchial tubes keep 

 these passages open. 



-! 249. The Cilia of the Air Passages. The inner surfaces 

 of the windpipe and bronchial tubes are lined with mucous 

 membrane, which serves to keep the parts moist. 



