328 CLINICAL APPLIED ANATOMY. 



this way, but the firm cohesion of the pleural layers renders it 

 possible for a small penetrating wound to damage both pleura 

 and lung without the necessary access of air to the pleural sac. 

 The same applies to compound fractures of the ribs. 



Air is sometimes aspirated into the pleural sac by respiratory 

 efforts during the careless performance of paracentesis. 



The apical portion of the parietal pleura projects into the neck, 

 and consequently air may enter the sac as the result of wounds 

 inflicted on it during a difficult tracheotomy, or operations at the 

 root of the neck, such as ligature of the subclavian artery. This 

 part of the sac may also be wounded by the splinters of a 

 fractured clavicle. 



The mediastinal portion of the parietal pleura may be per- 

 forated by abscesses of the mediastinum, and if these communicate 

 with the air or food passages, the pleura may become inflated. 

 Malignant disease of the oesophagus may produce a similar 

 result. 



The diaphragmatic portion of the left parietal pleura is im- 

 mediately above that portion of the diaphragm, which forms the 

 roof of the stomach chamber, and is sometimes perforated by 

 malignant disease of the stomach or transverse colon. When 

 this occurs, the gas from these organs may invade the pleura. 

 Abscesses of the liver or other sub-diaphragmatic collections 

 which already communicate with the exterior of the body may 

 effect a further communication with the pleural sac, and thus 

 afford a channel for the access of air to the latter. 



The lower part of the pleural sinus may be wounded during 

 operations on the kidney, and air may also enter the pleura of 

 the right side as the result of operations in the right sub- 

 diaphragmatic region. 



Any opening in the pleura must also involve the sub-pleural 

 planes of connective tissue, and so pneumothorax may be ac- 

 companied by emphysema of the connective tissue spaces 

 beneath the parietal pleura, or of the connective tissue of the 

 mediastinum. 



When air has free access to the pleural sac the pleural tension, 



