156 SURGICAL APPLIED ANATOMY. [Chap. x. 



inches above the lower margin of the thorax. Thus 

 it will be seen that the pleura and diaphragm may 

 be wounded in many places without the lungs being 

 involved. 



In penetrating wounds involving the pleura, air 

 may enter the pleural cavity, producing pneumo- 

 thorax, and this air may be subsequently pressed by 

 the respiratory movements into the subcutaneous 

 tissues through the wound in the parietal pleura, and 

 lead to surgical emphysema. The two layers of the 

 pleura are so intimately in contact with one another 

 in the normal thorax that it is questionable whether 

 the parietal pleura can be wounded without injury to 

 the visceral layer. In wounds of the lung without 

 external wound, as when that organ is torn by a 

 fractured rib, the air escapes from the lung into the 

 pleura, and may thence pass into the subcutaneous 

 tissues through the pleural wound, thus producing both 

 pneumo-thorax and emphysema. 



It is well to note that emphysema may occur 

 about certain non-penetrating wounds of the thorax 

 when they are of a valvular nature. In such cases 

 the air is drawn into the subcutaneous tissues during 

 one respiratory movement, and is forced by another 

 into the cellular tissue, the valvular nature of the 

 wound preventing its escape externally. When the 

 pleural " cavity " is opened, the lungs become more 

 or less collapsed ; yet a few cases have been recorded 

 where the lung has protruded at the time of the acci- 

 dent through the wound in the parietes. In such in- 

 stances the glottis must have been closed, and the lung 

 fully distended at the time of the injury ; and it must 

 be further assumed that the viscus was practically pro- 

 truded before air could enter the pleural space. It is 

 noticeable that these recent hernise are most common 

 at the anterior part of the chest where the lungs are 

 the most movable, and the injuries that bring them 



