160 



STRUCTURE OF THE LUNGS. 



cricoid cartilage ; c, the left bronchus ; d, the right bronchus ; e,f, g, its 

 ramifications in the right lung, j j ; A, i, ramifications of the left bron- 

 chus in the left lung, k L 



Fig. 77. Fig. 78. 



Human air-tubes. 



The heart and lungs. 



Fig. 78, arrangement of the heart and lungs, the latter in part section. 

 1, left auricle of the heart ; 2, right auricle ; 3, left ventricle ; 4, right 

 ventricle ; 5, pulmonary artery ; 6, aorta ; 7, superior vena cava ; 8, in- 

 nominata; 9, left primitive carotid; 10, left subclavian, ; 11, 12, upper 

 rings of trachea and cartilages of the larynx ; 13, upper lobe of right 

 lung; 14, upper lobe of left lung; 15, right pulmonary artery; 16, 16, 

 lower lobes of lungs. 



Fig. 79 illustrates the manner of 

 distribution of blood-vessels on the 

 air-cells of the lungs. 



As the blood to be arterialized 

 passes through the pulmonary capil- 

 laries, its discs can only move in sin- 

 gle files, and even then probably un- 

 dergo a compression which changes 

 their form. As soon, however, as 

 they escape into the larger vessels, 

 their elasticity enables them to recov- 



Distribution of capillaries on air-cells of the lungs. er their or igmal shape. 



By the aid of this elaborately constructed mechanism the air is brought 

 Three stages in to tne blood. There are three distinct stages through which 

 the introluc- Jt has to pass. The first is the filling of the trachea and 

 larger ramifications of the bronchial tubes : this is accom- 

 plished by atmospheric pressure, brought into play by muscular contrac- 



