248 THE VASCULAR SYSTEMS 



left cartilage, to the upper border of the second right cartilage. 

 Close to its origin it presents three small dilatations, the sinuses 

 of Valsalva, indicating the situation of the semilunar valves. 



Relations. In front, pulmonary artery, right appendix, thoracic 

 fascia, right pleura, pericardium, remains of the thymus gland; 

 he hind, root of the right lung, including right pulmonary ves- 

 sels, left auricle; to the right, right auricle, superior vena rava; 

 to the left, pulmonary artery. 



The transverse part of the arch passes backward and to the 

 left as far as the left side of the body of the fourth dorsal 

 vertebra. 



Relations. /// front, lungs and pleura, thymic remains, left 

 vagus, phrenic and superficial cardiac nerves, left superior 

 intercostal vein; behind, trachea, esophagus, thoracic duct, deep 

 cardiac plexus, left recurrent nerve; aborc, left innominate vein 

 and the branches of this portion of the aorta, viz., innominate, 

 left carotid, and subclavian arteries; below, left bronchus, bifur- 

 cation of the pulmonary artery, ductus arteriosus, left recurrent 

 nerve. 



The descending part of the arch descends to the lower border 

 of the fifth dorsal vertebra, ending in the thoracic aorta. 



Relations. In front, root of the left lung covered by pleura; 

 behind, left side of the body of the fifth dorsal vertebra; right 

 side, esophagus, thoracic duct; left side, left lung, covered by 

 pleura. 



The Branches of the Arch of the Aorta 



The branches of the arch are five coronary, right and left, 

 from the ascending part; and the innominate, left carotid, and 

 left subclavian, from the transverse part. The descending part 

 gives off no branches. 



The coronary arteries supply the heart and the coats of the 

 great vessels. They emerge on either side of the pulmonary 

 artery, between it and the corresponding appendix auriculae. 

 Each arises from a sinus of Valsalva, just above the free margin 

 of the corresponding semilunar valve, and is distributed to the 

 muscular substance of the heart, its valves and septa, running 

 along the grooves on its surfaces, and anastomosing freely with 

 the other, and, by means of twigs to the aorta and pulmonary 

 artery, with the pericardiac and bronchial vessels. Each 



