242 



THE RESPIRATORY APPARATUS 



middle, and posterior portions, bounded above by the 

 root of the neck, below by the diaphragm. Each 

 lung presents for examination an apex, a base, dia- 

 phragmatic, costal, mediastinal surfaces, and anterior, 

 posterior, and inferior borders. It is suspended within 

 the cavity by the root and the ligamentum pulmonale. 



FIG. 93 



Front view of the heart and lungs. (Gray.) 



During respiration the lung, covered by the visceral 

 pleura, is pressed against the walls of the thorax, 

 interlined by the parietal pleura, and friction is pre- 

 vented by a small amount of fluid, within the pleural 

 cavity, which continually bathes the approximating 

 surfaces. 



