THORACIC CAVITY 23 



vena cava. A secondary ridge, formed by the phrenic nerve 

 and the accompanying blood vessels, descends along the 

 elevation caused by the superior vena cava, crosses anterior 

 to the root of the lung, runs down along the posterior part 

 of the bulging due to the heart, and the anterior border 

 of the inferior caval elevation. Arching over the root of 

 the lung is a curved ridge, due to the upper part of the 

 vena azygos, as it passes anteriorly to join the superior cava. 

 Above the vena azygos and posterior to the superior cava, the 

 right lateral surface of the trachea, or main air tube, may 

 be seen or felt in the superior mediastinal region, and, 

 descending obliquely across it, from above downwards and 

 posteriorly, the right vagus nerve can be palpated or seen. 

 Posterior to the root of the lung and to the bulging 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 

 posteriorly are the bodies of the vertebrae and the posterior 

 parts of the ribs. Crossing the bodies of the vertebrae trans- 

 versely the right intercostal vessels may be visible or they 

 may be felt, and, descending along the line of the heads 

 of the ribs, the ganglionated trunk of the sympathetic can be 

 recognised by touch, if not by sight. 



The dissectors should examine next the mediastinum and 

 the posterior wall of the thorax on the left side (see Figs. 

 8, n, and 13). 



By inspection and palpation they will easily recognise the 

 positions of the larger and more important structures. 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 

 posteriorly and to the left, over 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 latter 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- 



