DISEASES OF THE RESPIRATORY ORGANS. 211 



ing with the essential lung membrane {air-cells, alveoli). 

 The tubes constitute a tree-like framework, upon which the 

 lung tissue proper is supported. The mass of this is elastic 

 tissue. The atmospheric air rushes into the respiratory 

 tract when the chest is enlarged by the muscles attached to 



Fig. 13.— Bronchial Tubes and Lungs, Posterior View (Sappey). 

 1, 1, summit of luugs ; 2, 2, base of lungs ; 3, trachea ; 4, right bronchus ; 5, divis- 

 ion to upper lobe of limg ; 6, division to lower lobe ; 7, left bronchus ; 8, divis- 

 ion to upper lobe ; 9, division to lower lobe ; 10, left branch of pulmonary 

 artery : 11, right branch ; 12, left auricle of heart ; 13, left superior pulmonary 

 vein ; 14, left inferior pulmonary vein ; 15, right superior pulmonary vein ; 16^ 

 right inferior pulmonary vein ; 17, inferior vena cava ; 18, left ventricle of 

 heart ; 19, right ventricle. 



it, because the lungs everywhere fit its walls closely ; and 

 air is expelled when the muscles are relaxed, the whole to 

 be explained on physical principles ; but the action of the 

 muscles is due to commands or nervous impulses originated 



