THORACIC AORTA. 417 



THE THORACIC AORTA. 



The THORACIC AORTA commences at the lower border of the third dorsal 

 vertebra, on the left side, and terminates at the aortic opening in the Diaphragm, 

 in front of the last dorsal vertebra. At its commencement, it is situated on the 

 left side of the spine ; it approaches the median line as it descends ; and, at its 

 termination, lies directly in front of the column. The direction of this vessel 

 being influenced by the spine, upon which it rests, it is concave forwards in the 

 dorsal region, and, as the branches given off from it are small, the diminution in 

 the size of the vessel is inconsiderable. It is contained in the back part of the 

 posterior mediastinum, being in relation, in front, from above downwards, with the 

 left pulmonary artery, the left bronchus, the pericardium, and the oesophagus ; 

 behind, with the vertebral column, and the vena azygos minor ; on the right side, 

 with the vena azygos major, and thoracic duct ; on the left side,^ with the left 

 pleura, and lung. The oesophagus, with its accompanying nerves, lies on the right 

 side of the aorta above ; in front of this vessel, in the middle of its course ; whilst, 

 at its lower part, it is on the left side, on a plane anterior to it. 



PLAN OF THE KELATIONS OF THE THORACIC AORTA. 



In front. 



Left pulmonary artery. 

 Left bronchus. 

 Pericardium. 

 (Esophagus. 



Right side. / \ Left side. 



(Esophagus (above). / Thoracic \ Pleura. 



Vena azygos major. 1 Aorta. I L e ft lung. 



Thoracic duct. V J (Esophagus (below). 



Behind. 



Vertebral column. 

 Vena azygos minor. 



Surgical Anatomy. The student should now consider the effects likely to be produced by 

 aneurism of the thoracic aorta, a disease of common occurrence. When we consider the great 

 depth of the vessel from the surface, and the number of important structures which surround it 

 on every side, it may be easily conceived what a variety of obscure symptoms may arise from dis- 

 ease of this part of the arterial system, and how they may be liable to be mistaken for those of 

 other affections. Aneurism of the thoracic aorta most usually extends backwards, along the left 

 side of the spine, producing absorption of the bodies of the vertebrae, causing extensive curva- 

 ture of the spine ; whilst the irritation or pressure on the cord will give rise to pain, either in 

 the chest, back, or loins, with radiating pain in the left upper intercostal spaces, from pressure 

 on the intercostal nerves; at the same time, the tumor may project back on each side of the 

 spine, beneath the integument, as a pulsating swelling, simulating abscess connected with dis- 

 eased bone ; or it may displace the resophagus, and compress the lung on one or the other side. 

 If the tumor extend forward, it may press upon and displace the heart, giving rise to palpitation, 

 and other symptoms of disease of that organ; or it may displace, or even compress, the oeso- 

 phagus, causing pain and difficulty of swallowing, as in stricture of that tube, and ultimately even 

 open into it by ulceration, producing fatal hemorrhage. If the disease make its way to either side, 

 it may press upon the thoracic duct; or it may burst into the pleural cavity, or into the trachea 

 or lung ; and lastly, it may open into the posterior mediastinum. 



BRANCHES OF THE THORACIC AORTA. 



Pericardiac. (Esophageal. 



Bronchial. Posterior mediastinal. 



Intercostal. 



The pericardiac are a few small vessels, irregular in their origin, distributed to 

 the pericardium. 

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