THE AORTA. 235 



into an arch, the thoracic portion and the abdominal por- 

 tion. The arch of the aorta is horseshoe-shaped. It begins 

 at the left ventricle of the heart (about the level of the 

 fourth dorsal vertebra), curves upward, forward, and to 

 the right on a level with the second right costal cartilage, 

 forming the ascending portion of the arch. It then curves 

 transversely backward and to the left to the lower border 

 of the second dorsal vertebra, forming the transverse 

 portion; then descends to the left of the vertebral column 

 to the fifth dorsal vertebra, whence it is continued down 

 the spine under the name of the thoracic aorta. The arch 

 of the aorta sends off five branches. 



From the ascending part of the arch are the right and 

 left coronary : 



Right Coronary. Branch from the aorta immediately 

 above its origin ; lies in right auriculo-ventricular groove ; 

 sends a branch down posterior interventricular groove. 



Left Coronary. Branch from the aorta immediately 

 above its origin ; lies in the anterior interventricular 

 groove and anastomoses with the descending branch of 

 the right coronary. 



From the transverse part of the arch are the innomi- 

 nate, left carotid, and left subclavian : 



Innominate. From superior part of right side of arch. 

 The largest branch of the arch passes upward to the right 

 sterno-clavicular joint, where it divides into the right sub- 

 clavian and right common carotid. 



Left Carotid. Passes upward behind the manubrian 

 and terminates in the neck on a level with the thyroid 

 cartilage, where it divides into the external and internal 

 carotids. The common carotid give off no branches. 



Left Subclavian. The last vessel from the arch of the 

 aorta curves into the root of the neck and terminates at 

 the lower border of the first rib. 



