

THE THORAX. 323 



artery, and lower portion of the superior vena cava (all 

 within the pericardium) ; the phrenic nerves and their 

 accompanying arteries ; the azygos vein (termination) ; the 

 roots of the lungs and some bronchial lymphatic glands. 



The posterior mediastinum is that portion of the space 

 between the pleurae laterally, the pericardium and roots of 

 the lungs in front, and the spine (below the fourth dorsal 

 vertebra) behind. 



It contains the descending and thoracic aorta, the oeso- 

 phagus, pneumogastric nerves, azygos veins, thoracic duct, 

 and lymphatic glands, sympathetic cord, ganglia, and 

 splanchnic nerves. 



Structures which traverse the superior opening of the 

 chest : 



Muscles. Sternohyoid, sternothyroid, longus colli. 



Arteries. Innominate, left common carotid, left subcla- 

 vian, internal mammary, superior intercostal. 



Veins. Left innominate, right internal jugular and sub- 

 clavian, inferior thyroids, and superior intercostals. 



Nerves. Phrenics, pneumogastrics, cardiac, sympathetic 

 cord, recurrent laryngeal. 



Other Structures. Thymus gland, thoracic duct, trachea, 

 oesophagus, apices of lungs, pleurae, cervical fascia. 



DISSECTION. 



If the pleurae have been preserved whole, remove the presenting portion. 

 Trace the phrenic nerves and save the arterial branch (very small) that accom- 

 panies them. 



Carefully dissect away the areolar tissue in the superior and anterior medi- 

 astina, exposing the remains of the thymus gland, the great vessels, and 

 pericardium. 



The Pleurae. 



Each pleura is a closed sack containing a lung, over 

 which it is reflected, passing into the fissures. This reflec- 



