TOPOGRAPHY OF THE LUNGS 



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proportions. Thus the general colour is red in the foetus, pink, in the infant, and grey mottled 

 with black in the adult. The dark colour is traceable to the carbonaceous matter carried into 

 the lungs from the atmosphere. 



In consistence the lung is soft and spongy, and when compressed between the fingers, 

 emits a crackling sound. Arnong the physical properties the elasticity of the lung is quite 

 remarkable. Under ordinary conditions the pressure of the air in the lung keeps the alveoli 

 and the organ as a whole distended, but when the pleura has been opened and the air pressure 

 equaUsed without and within, the lung collapses. 



Topography.^The apices of the lungs extend upward as high as the first thoracic vertebra- 

 a level considerably higher than the superior margin of the sternum (figs. 997, 998). The sub, 

 clavian vein and artery and the brachial plexus, together with the anterior scalene muscle, 

 control to a certain degree the height reached. There seems to be no constant difference be- 

 tween the levels attained by the apices of the two lungs. The extent to which the apex rises 

 above the clavicle is rarely more than 3.5 cm. (Merkel), and will, of course, vary with individual 

 differences in the position and form of this bone. The average is not over 2.5 cm. (1 in.). 



The base of the lung, resting on the diaphragm, is separated by that thin partition from the 

 underlying abdominal viscera: thus beneath the base of the right lung is the right lobe of the 

 liver, while under the left lung are the left lobe of the hver, the fundus of the stomach, and the 

 spleen. The position of the apex changes very little in respiration, and the same holds true for 



Fig. 997. — Position of the Lungs from Before. (Merkel.) 

 The parietal pleura is shaded and outlined in black. 



the hinder bulky part of the lung. The latter rests against the side of the vertebral column in 

 the deep hollow of the angles of the ribs, and reaches below to the level of the eleventh costo- 

 vertebral joint (fig. 998). The anterior margins (fig. 997) descend in curves from behind the 

 sterno-clavicular joints, and run near together a little to the left of the median line. At the 

 level of the sixth costo-sternal junction the anterior margin of the right lung turns lateral- 

 ward to follow the sixth costal cartilage. The anterior margin of the left lung turns lateralward 

 along the fourth costal cartilage as far as the para-sternal line, descending in a curve to the 

 lingula and thus forming the cardiac incisure. The positions of the inferior margins (figs. 

 997, 998) of the two lungs are practically ahke in their positions. Each extends in a curve cov- 

 vex downward, behind the sixth costal cartilage in its entire length, crosses the costo-chondral 

 junction of the sixth rib to the superior margin of the eighth rib in the axillary line, and so to 

 the ninth or tenth rib in the scapular line, whence they run horizontally medialward to the 

 eleventh costo-vertebral joint.* 



* These relations are the mean between the conditions observed in the cadaver and as found 

 by physical examination of the living. In old age the inferior margins of the lungs reach a 

 level one or two intercostal spaces lower than is the case in adult hfe (Mehnert). 

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