THE ARCH OF THE AORTA. 



543 



ed<ie of the left posterior semilunar valve, a little higher than the right; it' passes 

 forward between the pulmonary artery and theJlelt^uTicjilar_appiidix, and divides 

 into two branches. OTTfieseT "ou^tfansverse) passes transversely outward in the 

 left auriculo-ventricular groove, and winds around the left border of the heart 

 into its posterior surface, where it anastomoses with the transverse branch of the 

 right coronary ; the other (descending) descends along the anterior interventricu- 

 lar groove to the apex of the heart, where it anastomoses with the descending 

 branches of the right coronary % The left coronary supplies the left auricle and 

 its appendix, both ventricles, and numerous small branches to the pulmonary 

 artery, and commencement of the aorta. 1 



Peculiarities. These vessels occasionally arise by a common trunk, or their number may 

 be increased to three, the additional branch being of small size. More rarely, there are two 

 additional branches. 



THE ARCH OF THE AORTA. 



The arch, or transverse aorta, commences at the upper border of the second 

 chondro-sternal articulation of the right side, and passes from right to left, and 

 from before backward, to the left side of the lower border of the fourth dorsal 

 vertebra behind. Its upper border is usually about an inch below the upper mar- 

 gin of the sternum. 



Relations. Its anterior surface is covered by the pleurae and lungs and the 

 remains of the thymus gland, and crossed toward the left side by the left pneumo- 

 gastric and phrenic nerves and superior cardiac branches of the left sympathetic, 

 and by the left superior intercostal vein. Its posterior surface lies on the trachea, 

 just above its bifurcation, on the great, or deep, cardiac plexus, the oesophagus, 

 thoracic duct, and left recurrent laryngeal nerve. Its upper border is in relation 

 with the left innominate vein, and from its upper part are given off the innom- 

 inate, left common carotia, and left subclavian arteries. Its loicer border is in 

 relation with the bifurcation of the pulmonary artery, the remains of the ductus 

 arteriosus. which is connected with the left division of that vessel, and the super- 

 ficial cardiac plexus : the left recurrent laryngeal nerve winds round it from 

 before backward, whilst the left bronchus passes below it. 



PLAN OF THE RELATIONS OF THE ARCH OF THE AORTA. 



Above. 



Left innominate vein. 

 Innominate artery. 

 Left carotid. 

 J.ieft subclavian. 

 In From. 

 Pleurae and lungs. 

 Remains of thymus gland. 

 Left pneumogastric nerve. 

 Left phrenic nerve. 

 Left superior cardiac ner 

 Left superior intercostal vein. 



Below. 



Bifurcation of pulmonary artery. 

 Remains of ductus arteriosus. 

 Superficial cardiac plexus. 

 Left recurrent nerve. 

 Left bronchus. 



Peculiarities. The height to which the aorta rises in the chest is usually about an inch 

 below the upper border of the sternum : but it may ascend nearly to the top of that bone. 

 Occasionally it is found an inch and a half, more rarely two or even three inches, below this 

 point. 



1 According to Dr. Samuel West, there is a very free and complete anastomosis between the two 

 coronary arteries < Lancet, June '2. 1<S3. p. 945 . This, however, is not the view generally held by 

 anatomist., for, with the exception of the anastomosis mentioned above in the auriculo-ventricular and 

 interventricular grooves, it is believed that the two arteries only communicate by very small vessels 

 : n the substance of the heart. 



Behind. 

 Trachea. 



Deep cardiac plexus. 

 (Esophagus. 

 Thoracic duct. 

 Left recurrent nerve. 





