THORACIC CAVITY 25 



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 subclavian artery, and then downwards and 

 posteriorly across the arch of the aorta, to disappear posterior 

 to 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. 



When the inspection and palpation of the structures 

 lying in relation with the mediastinal and posterior parts of 

 the costal pleura is satisfactorily completed, the greater part 

 of the pleura should be removed on both sides. 



Dissection. Make a longitudinal incision through the mediastinal pleura 

 immediately anterior to the phrenic nerve and a similar incision posterior 

 to the nerve. 



From the anterior longitudinal incision an incision should be carried 

 anteriorly, at the level of the middle of the root of the lung, and from 

 the posterior longitudinal incision another cut should be carried posteriorly 

 to the front of the root of the lung and then along its anterior 

 surface. Then the root of the lung should be turned anteriorly and 

 an incision should be made on its posterior surface parallel with that 

 already made on the anterior surface. This incision should be carried 

 posteriorly from the root of the lung across the posterior part of the wall 

 of the mediastinum, and then laterally, across the posterior wall of the 

 thorax. When the incisions are completed four flaps will be marked out, 

 two anterior and two posterior. 



The upper anterior flap on the right side must be turned anteriorly to the 

 level of the anterior border of the superior vena cava, where it may be 

 cut away, the portion of the pleura extending from the superior vena cava 

 to the sternum being left in situ. The upper anterior flap on the left 

 side should be turned anteriorly to the anterior part of the arch of the aorta 

 and the anterior surface of the upper part of the pericardium where it 

 should be cut away, the part extending further forwards to the sternum 

 being left in position. The lower anterior flap on each side must also be 

 turned anteriorly till the anterior part of the pericardium is reached. There 

 it may be cut away, but the portion of pleura extending from the peri- 

 cardium to the sternum should not be interfered with at present. 



The posterior flaps on each side should be completely removed, care 

 being taken to avoid injury to any of the structures which they cover. 



When the pleura has been removed, both dissectors should study care- 

 fully the structures exposed on each side, commencing with the right 

 side. 



