348 PRACTICAL ANATOMY. 



applied to the wall of the chest; the inner surface is 

 flattened, slightly concave, for the accommodation of the 

 heart, and posteriorly presents the hilum, for the entrance 

 of the bronchi, vessels, and nerves. 



The right lung presents three lobes ; the left lung 

 two. The lobes are formed by deep fissures, commencing 

 at the anterior border and extending deeply upward and 

 inward. The left lung is the longer; the right the 

 broader and heavier. The two lungs weigh forty-two 



FIG. 150. HEART AND LUNGS. 



1, right ventricle ; 3, i ight auricle : 5, pulmonary artery ; 9, aorta : 10, supe ior cava ; 

 i, root of lung ; 21, 22, 23, upper, middle, and lower lobes of right lung ; 24, 25, upper and 



20, or 



lower lobes of left lung. 



ounces, have an average specific gravity of about 0.5, 

 and hence float in water ; but, if consolidated by in- 

 flammatory effusions, or if collapsed, or prior to the re- 

 spiratory act, they will sink in water. At birth, the lungs 

 are of a rose-pink in color ; but, as age advances, they 

 become darker, often mottled and bluish. On the sur- 

 face of the lungs are seen polygonal spaces, about the 

 size of a split pea, which correspond to the lobules. 



The structure of the lungs can best be understood by 



