194 THE CIRCULATORY APPARATUS 



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. 



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. 



The descending part of the arch descends to the 

 lower border of the fifth dorsal vertebra, ending in 

 the thoracic aorta. 



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. 



The innominate (brachiocephalic) artery is the largest 

 branch. It arises in front of the left carotid, and runs 

 obliquely to the right sternoclavicular joint, where 

 it divides into the right common carotid and right 

 subclavian. 



The common carotid arteries are identical in course, 

 branches, and relations in the neck, but differ in 

 their origin. Thus, the right is a branch of bifurca- 

 tion of the innominate, while the left is a primary 

 branch of the transverse aorta. 



The external carotid artery runs from the bifurcation 

 of the common carotid to the space between the 

 neck of the condyle of the mandible and the audi- 

 tory meatus, and there divides into the superficial 

 temporal and internal maxillary. 



The internal carotid artery is a very tortuous vessel, 

 and at its origin is farther from the median line than 

 the external carotid, deriving the name "internal" 

 from its distribution. For description it is divided 

 into four parts: the first, or cervical; the second, or 

 petrous, is in the carotid canal; the third, or cavernous 



