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THE ANIMALS AND MAN 



either side of the partition. The trachea (fig. 175, 3) divides 

 within the membranes into two branches or bronchi (fig. 

 175, 4) which pass through the membrane into the lungs. 

 The bronchi divide, in the lungs, into smaller and smaller 



FIG. 175. Bronchi and lungs, posterior view, showing position of heart. 

 1, 1, summit of lungs; 2, 2, base of lungs; 3, trachea; 4, right bronchus; 

 5, branch to upper lobe of lung; 6, branch to lower lobe; 7, left bronchus; 

 8, branch to upper lobe; 9, branch 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 auricle of heart; 19, right ventricle. (After 

 Sappey.) 



branches, each culminating in a minute vessel or bronchiole 

 (fig. 176) which ends in a small air sac or alveolus. The 

 lungs are in reality masses of these tiny air sacs surrounded 

 by connective tissue. It is through the thin walls of the 



