THE THORACIC AORTA 



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hiatus in the diaphragm. At its commencement, it is situated on the left of the 

 vertebral column; it approaches the median line as it descends; and, at its termina- 

 tion, lies directly in front of the column. The vessel describes a curve which is 

 concave forward, and as the branches given off from it are small, its diminution 

 in size is inconsiderable. 



Highest intercostal artery 



Highest intercostal vein 



Rami communicantes 

 Lig. arteriosum 





FIG. 530. The thoracic aorta, viewed from the left side. 



Relations. It is in relation, anteriorly, from above downward, with the root of the left lung, 

 the pericardium, the esophagus, and the diaphragm; posteriorly, with the vertebral column 

 and the hemiazygos veins; on the right side, with the azygos vein and thoracic duct; on the lejt 

 side, with the left pleura and lung. The esophagus, with its accompanying plexus of nerves, 

 lies on the right side of the aorta above; but at the lower part of the thorax it is placed in front 

 of the aorta, and, close to the diaphragm, is situated on its left side. 



Peculiarities. The aorta is occasionally found to be obliterated at the junction of the arch 

 with the thoracic aorta, just below the ductus arteriosus. Whether this is the result of disease, 

 or of congenital malformation, is immaterial to our present purpose; it affords an interesting 

 opportunity of observing the resources of the collateral circulation. The course of the anastomos- 



