THORACIC CAVITY 31 



due to the heart, the oesophagus may be recognised in the 

 posterior mediastinal area, either by touch or sight, or both. 

 Somewhat posterior to the oesophagus the margin of the 

 ascending portion of the vena azygos may be noted, and 

 still further back are the bodies of the vertebrae and 

 the posterior parts of the ribs. Crossing the bodies of the 

 vertebrae horizontally, the right intercostal vessels may be 

 visible or they may be felt, and, descending along the line 

 of the heads of the ribs, the sympathetic trunk and the roots 

 of the greater splanchnic nerve can be recognised by touch, 

 if not by sight. 



Examine next the mediastinum and the posterior wall of 

 the thorax on the left side (see Figs. 9, 12, and 14). 



By inspection and palpation the positions of the larger 

 and more important structures are easily recognisable. Below 

 and anterior to the root of the lung the mediastinal pleura is 

 bulged much more laterally on the left than on the right 

 side by the heart covered by the pericardium. Arching 

 backwards and to the left, above the root of the lung, in the 

 superior mediastinal area, is the arch of the aorta, and from 

 its posterior end the descending aorta runs downwards, in the 

 posterior mediastinal area, first posterior to the root of the 

 lung, and then posterior to the heart, but separated, in part, 

 from the heart by the oesophagus, which diverges towards the 

 left side in the lower part of the thorax. Above the arch of 

 the aorta the left common carotid and subclavian arteries 

 and the oesophagus can be distinguished, in the above order 

 antero - posteriorly. A long, slender secondary ridge, pro- 

 duced by the left phrenic nerve and the accompanying vessels 

 descends along the line of the common carotid artery, crosses 

 the arch of the aorta, and then continues along the side 

 of the pericardium. Above the aortic arch, and posterior to 

 the ridge caused by the phrenic nerve, the left vagus nerve 

 can be seen or felt, as it runs downwards along the anterior 

 border of the left subclavian artery, and then downwards and 

 backwards across the arch of the aorta, to disappear behind 

 the root of the lung. Posterior to the descending aorta the 

 sympathetic trunk of the left side can be seen or palpated as 

 it descends along the line of the heads of the ribs. 



Anterior to the pericardium and the aortic arch and its 

 branches, the mediastinal pleura passes forwards to the back of 

 the sternum, in contact with the pleura of the opposite side. 



