84 THORAX 



contrary it presents four dilatations, three at the commence- 

 ment, the aortic sinuses (Valsalva), and one along the right 

 border, the great sinus of the aorta. The latter is merely an 

 indefinite bulging along the right border of the vessel. 



Relations. The lower part of the ascending aorta lies 

 posterior to the upper part of the conus arteriosus and the lower 



nternal 

 mammary 

 vessels 



Pericardium 



Ascending aorta 



Right phrenic 

 nerve 



Superior 

 vena cava 



Thoracic duct 



Descending 

 aorta 



Vena hemiazygos 

 accessoria 



Right pulmon- 

 ary artery 



Bifurcation of 

 trachea 

 Right vagus 

 p \ nerve 



Bronchial artery 



Vena azygos 



Intercostal 

 artery 



Sympathetic 

 trunk 



FIG. 42. Transverse section through the Mediastinal Space at the 

 level of the fifth dorsal vertebra. 



part of the stem of the pulmonary artery ; but the upper part 

 is in direct relation with the anterior wall of the pericardium, 

 which separates it from the anterior part of the mediastinal 

 surface of the right pleura and lung. Posterior to the ascend- 

 ing aorta, from below upwards, are the left atrium, the right 

 pulmonary artery and the right bronchus. To the right are 

 the right auricle below and the superior vena cava above ; and 



