606 THE LUNGS. 



The form of the lungs is conical, the apex being above, 

 rounded, and seen to rise from one to two inches above 

 the level of the first rib ; the base below, and concave, to 

 correspond to the convex surface of the diaphragm. The 

 base of the lung presents, from before, obliquely downward 

 and backward, precisely in the direction of the diaphragm, 

 and consequently makes the vertical extent of the lungs 

 behind, which reach from the first to the last rib, much 

 greater than in front, where the extent is only from the 

 first rib to the lower end of the second bone of the sternum. 



FIG. 196. 



l-L 



The size of the lungs is in a direct ratio with the capac- 

 ity of the thorax. The average volume of air they are 

 capable of containing, after an ordinary inspiration, is esti- 

 mated at 140 cubic inches; and after expiration, at 110 

 cubic inches. From thirty to forty cubic inches is the 

 average estimate of air inhaled at each inspiration. 



The specific gravity and density of the lungs are less than 



FIG. 196 represents the Lungs, their anterior surface, with the Heart. 1 The 

 heart right ventricle. 2 Pulmonary artery. 3 Left bronchus. 4 Vena in- 

 nominata its junction. 8 Right auricle. 9 Pulmonary vein. 11 Superior 

 lobe of right lung. 12 Middle lobe. 13 Inferior lobe. 14 Superior lobe of 

 left lung. 15 Inferior lobe. 



