184 Innominate Artery 



from its fellow, but the supra- and posterior scapular arteries would be 

 useless. The superior intercostal helps by its anastomosis with the 

 first aortic intercostal, but its anastomosis with the occipital could not 

 serve ; by its thoracic branches, namely, the short, the acromial, the 

 axillary, the alar, and the long ; and by the ending of the subscapular 

 on the chest, all of which anastomose with aortic branches. 



Aneurysm of the innominate artery causes a bulging to the 

 right of the manubrium, especially into the first right space. Eventually 

 it may cause absorption of the upper ribs of right side, and of the 

 manubrium, and appear as a pulsating tumour on the front of the chest. 

 It is often impossible to diagnose it from aneurysm of the ascending 

 aorta ; indeed, both of those trunks are often dilated at the same 

 time. 



The dilatation interferes with the due filling of the trunks coming 

 from the innominate, so that the carotid and radial pulse of the right 

 side are altered. The left innominate vein (p. 186), and perhaps the 

 right also, is compressed ; the trachea is pushed towards the left side, 

 the voice is feeble, and respiration may be spasmodic and difficult. 



The frequency of the occurrence of aneurysm of the innominate 

 artery may be due to the fact that the root of that vessel, together 

 with the right side of the first part of the arch, receives the shock 

 of the ventricular stroke. 



Relations of the pulmonary artery. A coronary artery comes 

 forward from the aorta on either side of its root. Springing from the 

 right ventricle, the pulmonary artery is at first in front of the aorta, but 

 as the first part of the arch ascends to the right the pulmonary artery is 

 soon found to its left side. As these two large trunks were developed 

 together, they lie in the same serous tube of pericardium. The bifur- 

 cation of the pulmonary artery is connected with the left side of the 

 concavity of the aortic arch by the ductus arteriosus.- (For Root of 

 Lung -u. p. 194.) 



The thoracic aorta continues the third part of the aortic arch from 

 the lower border of the fifth (p. 179) to the twelfth dorsal vertebra, 

 where, passing through the diaphragm, it becomes the abdominal aorta. 

 At first towards the left side of the dorsal column, it gradually inclines 

 towards the middle line ; and, lying upon the spine, it has also a curve 

 with the concavity forwards. 



Relations. It rests upon the vertebral column and the left inter- 

 costal veins, and has in front some of the root of the left lung, the peri- 

 cardium and heart, and the oesophagus. To the left are the pleura and 

 lung; and just above the diaphragm the oesophagus also is to the left. 

 To the right are the oesophagus above ; the thoracic duct and vena 

 azygos major, and the spinal column. 



Aneurysm of the thoracic aorta may extend backwards, causing 

 erosion of the vertebra? and ribs, producing spinal curvature ; irritating 

 the intercostal nerves, and causing ' pleurodynia,' or neuralgia in the 



