io 4 



THORAX 



cesophageal branches, and some small and irregular media- 

 stinal and pericardial branches. The posterior branches are 

 nine pairs of aortic intercostal arteries and one pair of sub- 

 costal arteries. 



Relations. Anterior to the thoracic part of the descending 

 aorta, from above downwards, are the root of the left lung ; 

 the upper part of the posterior wall of the pericardium, 

 separating the aorta from the left atrium ; the oesophagus, 

 separating the aorta from the lower part of the posterior wall 

 of the pericardium ; and the crura of the diaphragm, which 

 separate the lower portion of the thoracic aorta from the 



- Pericardium 



Diaphragm 



-Diaphragm 

 CEsophagus 



Thoracic aorta 

 Left pleura 



Thoracic duct 

 ~"~ Right pleura 

 ~Vena azygos 



FIG. 51. Tracing of a section through the lower part of the Posterior 

 Mediastinum, where its anterior wall is formed by the diaphragm. 



omental bursa of the peritoneum and from the posterior 

 surface of the caudate lobe (O.T. Spigelian) of the liver. 

 Posteriorly are the vertebral column, its own intercostal and 

 subcostal branches, the hemiazygos and accessory hemiazygos 

 veins ; and it is overlapped posteriorly in the upper part of its 

 extent by the left pleura and lung. Along its right side^ in its 

 whole length, are the thoracic duct and the vena azygos, and 

 anterior to them, from the fifth to the lower part of the 

 seventh thoracic vertebra, lies the oesophagus. At a lower 

 level a mass of areolar tissue separates the aorta from the 

 right pleura and lung. On its left side it is in relation with 

 the left pleura and lung. 



Dissection. Turn the remains of the lower part of the oesophagus down- 

 wards towards the diaphragm. Clean the thoracic duct, the right aortic 

 intercostal arteries, and the hemiazygos and accessory hemiazygos veins, 

 which lie posterior to the oesophagus. Then trace the thoracic duct in the 



