THE THORAX 



941 



The middle mediastinum lies behind the anterior, and below the 

 superior, mediastinum, and is the \\-idest part of the interpleural 

 space. 



Contents. — These are as foUows: (i) the heart, enclosed in the 

 pericardium; (2) the ascending aorta; (3) the trunk of the pul- 

 monary artery; (4) the lower half, or intrapericardial portion, of the 

 superior vena cava; (5) the phrenic nerves and the superior phrenic 



Parietal Pleura 

 Pknral Interval 



Internal Mammary Vessels 



Pulmonarj- 

 Pleura 



Left Vagu 

 Nerve 



Right Vagus Nerve 



Thoracic Duct 



Right Azygos Vein 



Fig. 384. — Transverse Section of the Thorax through the Second 

 Sternebra in Front and the Body of the Ninth Thoracic Ver- 

 tebra Behind, showing the Reflections of the Pleura and the 

 Position of the Viscera. 



S. Sternum 

 A.M. Anterior Mediastinum 

 A. A. Ascending Aorta 

 P.A. Pulmonarj- Artery 

 R.A.A. Right Auricular Appendix 

 R.A. Right Auricle 

 M.M. Middle Mediastinum 

 L..A. Left Auricle 



P.M. Posterior Mediastinum 



O. CE^phagus 

 D.A. Descending Thoracic Aorta . 

 T.V. Thoracic Vertebra 



M. Middle Lobe of Right Lung 

 R.U. Right Upper Lobe 

 R.L. Right Lower Lobe 

 L.U. Left Upper Lobe 

 L.L. Left Lower Lobe 



vessels; (6) the bifurcation of the trachea; and (7) the roots of the 

 lungs. 



The posterior mediastinum is situated behind the pericardium, 

 and below the posterior part of the superior mediastinum, with 

 which latter it is continuous. Its boundaries are as foUows: in 

 front, the pericardium, and below this the posterior part of the 

 diaphragm; behind, the bodies of the thoracic vertebrae below the 

 level of the lower border of the body of the fourth; and laterally, 

 the mediastinal pleura of each side as it extends from the back of 

 the root of the lung to the side of the vertebraj colmmi. 



