972 



THE ORGANS OF VOICE AND RESPIRATION. 



The anterior mediastinum is bounded in front by the sternum, on each side by 

 the pleura, and behind by the pericardium. It is narrow above, but widens out 

 a little below, and, owing to the oblique course taken by the left pleura, it is 

 directed from above obliquely downward and to the left. Its anterior wall is 

 formed by the left Triangularis sterni muscle and the fifth, sixth, and seventh left 



FIG. 536. The posterior mediastinum. 



costal cartilages. It contains a quantity of loose areolar tissue, some lymphatic 

 vessels which ascend from the convex surface of the liver, two or three lymphatic 

 glands (anterior mediastinal glands), and the small mediastinal branches of the in- 

 ternal mammary artery. 



The middle mediastinum is the broadest part of the interpleural space. It con- 

 tains the heart enclosed in the pericardium, the ascending aorta, the lower half of 



