BRANCHES OF THE THORACIC AORTA. 547 



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 easily be 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 backward along the left 

 side of the spine, producing absorption of the bodies of the vertebrae, with curvature 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 backward on each side of the spine, beneath the 

 integument, as a pulsating swelling, simulating abscess connected with diseased bone, or it may 

 displace the oesophagus 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 oesophagus, causing pain and 

 difficulty of swallowing, as in stricture of that tube ; and ultimately even open into it oy ulcera- 

 tion, producing fatal haemorrhage. If the disease extends to the right 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. CEsophageal. 



Bronchial. Posterior Mediastinal. 



Intercostal. 



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

 the pericardium. 



The bronchial arteries are the nutrient vessels of the lungs, and vary in num- 

 ber, size, and origin. That of the right side arises from the first aortic intercostal, 

 or by a common trunk with the left bronchial from the front of the thoracic aorta. 

 Those of the left side, usually two in number, arise from the thoracic aorta, one a 

 little lower than the other. Each vessel is directed to the back part of the corre- 

 sponding bronchus along which it runs, dividing and subdividing along the bron- 

 chial tube, supplying them, the cellular tissue of the lungs, the bronchial glands, 

 and the oesophagus. 



The oesophageal arteries, usually four or five in number, arise from the front 

 of the aorta, and pass obliquely downward to the oesophagus, forming a chain of 

 anastomoses along that tube, anastomosing with the oesophageal branches of the 

 inferior thyroid arteries above, and with ascending branches from the phrenic and 

 gastric arteries below. 



The posterior mediastinal arteries are numerous small vessels which supply the 

 glands and loose areolar tissue in the mediastinum. 



The Intercostal arteries arise from the back of the aorta. They are usually 

 nine in number on each side, the two superior intercostal spaces being supplied 

 by the superior intercostal, a branch of the subclavian. The second space usually 

 receives a considerable bi'anch from the first aortic intercostal, which joins with 

 the branch from the superior intercostal of the subclavian. The branch which 

 runs along the lower border of the last rib is named the subcostal artery. The 

 right intercostals are longer than the left, on account of the position of the aorta 

 on the left side of the spine : they pass outward, across the bodies of the vertebrae, 

 to the intercostal spaces, being covered by the pleura, the oesophagus, thoracic 

 duct, sympathetic nerve, and the vena azygos major ; the left, passing outward, 

 are crossed by the sympathetic ; the upper two are also crossed by the superior 

 intercostal vein, the lower by the azygos minor veins. In each intercostal space 

 the artery passes outward, at first lying upon the External intercostal muscle, 

 covered in front by the pleura and a thin fascia. It then passes between the two 

 layers of Intercostal muscles, and, having ascended obliquely to the lower border 

 of the rib above it, is continued forward in the groove on its lower border and 

 anastomoses with the anterior intercostal branches of the internal mammary. 

 The first aortic intercostal anastomoses with the superior intercostal, and the last 

 three pass between the abdominal muscles, inosculating with the epigastric in front 



