THE LUNGS. 607 



that of any other organ. This depends on the presence of 

 the air. Their absolute weight is less in the foetus than 

 after birth. In the former the proportion to the body is 

 as one to sixty ; in the latter, as one to thirty. 



The elasticity of the lungs is very considerable, and it is 

 by this property they are aided in the act of expiration. 

 This property is demonstrated by the collapsing of the 

 lungs on opening the chest. Before the chest is opened, 

 the organs are not collapsed, as the air they contain, 

 by the pressure from within, keeps them constantly dis- 

 tended; but when the chest is opened, the atmospheric 

 pressure from without balances that within, and then the 

 elasticity has the opportunity of exerting its influence, 

 and produces the state of collapse. 



The color of the lungs varies according to the age. In 

 the foetus it is found to be of a reddish brown, after 

 birth of a light rose or pinkish hue ; in the adult it is 

 grayish, interspersed with black, which presents the form 

 either of lines, patches, or points, and in old age these 

 black deposits increase. 



The surfaces of the lungs are external and internal. The 

 external is convex and corresponds to the concavity of the 

 rjbs, presenting a variety of different shaped figures sep- 

 arated by intermediate dark lines. The internal is con- 

 cave for receiving the pericardium and heart. The lungs 

 are divided into two lobes by a deep fissure commencing 

 behind and below the apex, and descending obliquely 

 downward and forward to the front of the base. Upon the 

 right lung there is another fissure, which is short, and 

 leads from the middle of the great one forward to the an- 

 terior margin, thus making another lobe for the right 

 lung, which is in the middle, to the other two. The rela- 

 tive position of the two lobes is, the one superior and 

 anterior, the other inferior and posterior. Sometimes the 

 left lung is found with three lobes, and the right with 

 four or more. 



The anterior edge is short, thin, and oblique. The 

 posterior edge is long, thick, round, and vertical. 



