112 



THORAX 



the fibrous sac of the pericardium, and is ensheathed by 

 a covering of the serous sac which is common to it and the 

 stem of the pulmonary artery. The lumen of the ascending 

 portion of the aorta is not of uniform diameter; on the 

 contrary, it presents four dilatations, three at the commence- 



Thoracic duct 



Descending 

 aorta 



Vena hemiazygos 

 accessoria 



Internal 

 mammary 



Pericardium 



Ascending aorta 



Right phrenic 

 nerve 



Superior 

 vena cava 



Right pulmon- 

 ary artery 



Bifurcation of 

 trachea 

 Right vagus 

 nerve 

 Bronchial artery 



Vena azygos 



Intercostal 

 artery 



Sympathetic 

 trunk 



FIG. 56. Transverse section through the Mediastinum at the 

 level of the fifth thoracic vertebra. 



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

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

 ill-defined 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 

 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 



