THE MEDIASTINUM. 113 



portant branches of the ascending aorta are the coronary arteries, which arise from the right and 

 left aortic sinuses (sinuses of Valsalva). The right coronary artery runs backward in the right 

 coronary groove (between the auricle and ventricle), and then downward in the posterior inter- 

 ventricular groove to the cardiac apex. The left coronary artery immediately divides into an 

 anterior branch, which passes downward in the anterior interventricular groove, and a transverse 

 branch which runs in the left coronary groove. 



The Arch of the Aorta. The arch of the aorta commences at the origin of the innominate 

 artery and extends to the left side of the body of the third or fourth dorsal vertebra, where it be- 

 comes the descending aorta. It runs over the root of the left lung in an approximately sagittal 

 direction (Fig. 53) and, in contrast to the ascending aorta, continually becomes more distant 

 from the anterior thoracic wall. The left innominate vein lies in front of the upper convex mar- 

 gin of the aortic arch and passes obliquely downward and to the right in front of the origins of 

 the three main branches of the aorta, the innominate, the left common carotid, and the left 

 subclavian arteries. The aortic arch does not extend upward beyond the sternal attachment 

 of the first rib ; its highest point is situated at about the level of the center of the manubrium. 

 From the course of the aortic arch it follows that the innominate artery is nearest to the anterior 

 thoracic wall, the left common carotid is further removed, and the left subclavian is the most 

 distant of the three vessels. The left subclavian artery projects into the upper portion of 'the 

 dome of the pleura and produces the subclavian groove upon the apex of the left lung (see page 

 102 and Fig. 48). The left inferior laryngeal nerve, a branch of the left pneumogastric, passes 

 backward and upward around the aortic arch (see page 68 and Plate 10). It is the motor nerve 

 of the larynx, and is often compressed by aortic aneurysms, producing one of the first symptoms 

 of this affection a paralysis of the left vocal cord. Aneurysms of the aortic arch may produce: 

 venous stasis of the head, of the neck, and of the left upper extremity by pressing upon the left 

 innominate vein or its tributaries (Plate 9) ; deficient ventilation of the lungs (dyspnea) by pres- 

 sure upon the trachea, or only of the left lung by pressure upon the left bronchus and the left 

 pulmonary artery; paralysis of the left vocal cord by pressure upon the left inferior laryngeal 

 nerve, the motor nerve of the muscles of the interior of the larynx; and dysphagia, from pressure 

 upon the left pneumogastric nerve and upon the esophagus. Such aneurysms may rupture (Plate 

 7) into the trachea and left bronchus (hemoptysis) or, if the aneurysm is situated posteriorly, 

 into the esophagus (hematemesis). The comprehension of all the preceding possibilities will 

 be facilitated by a careful study of Plate 10. 



The Thoracic Descending Aorta. The thoracic descending aorta extends from the left 

 side of the body of the third or fourth dorsal vertebra to the aortic opening in the diaphragm, in 

 which situation it has usually reached the median line. After the removal or displacement 

 of the left lung the aorta may consequently be seen through the mediastinal pleura at the left 

 side of the vertebral column (Plates 8, a, and 17). The esophagus is at first upon the right s 

 and then in front of the vessel (Fig. 54) with which it is united by loose connective t 

 intercostal arteries arise from the posterior surface of the aorta (see page 96); there are nine 

 pairs for the lower nine intercostal spaces and one pair for the lower border of the twelfth r 

 In addition to these vessels, there are many small visceral branches which are not part: 



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