THE INNOMINA TE A R TER } r 585 



plving the left side, and the carotid and subclavian (which arise separately) the right side. In 

 other eases, where the aorta takes its usual course, the two carotids may be joined in a common 

 trunk, and the subclavians arise separately from the arch, the right subclavian generally arising 

 from the left end of the arch. 



In some instances other arteries are found to arise from the arch of the aorta. Of these the 

 most common are the bronchial, one or both, and the thyroidea ima; also the internal mammary 

 and the inferior thyroid have been seen to arise from this part of the vessel. 



The Innominate Artery (A. Anonyma) (Figs. 432 and 433). 



The innominate or brachiocephalic artery is the largest branch given off from 

 the arch of the aorta. It arises, on a level with the upper border of the second 

 right costal cartilage, from the commencement of the arch of the aorta in front 

 of the left carotid, and, ascending obliquely to the upper border of the right sterno- 

 clavicular articulation, divides into the right common carotid and right subclavian 

 arteries. This vessel varies from an inch and a half to two inches in length. 



Relations. In front, it is separated from the first piece of the sternum by the Sternohyoid 

 and Sternothyroid muscles, the remains of the thymus gland, the left innominate and right 

 inferior thyroid veins which cross its root, and sometimes the inferior cervical cardiac branch 

 of the right vagus. Behind, it lies upon the trachea, which it crosses obliquely, and continuing 

 upward it lies in the right pleura. On the right side is the right innominate vein, right vagus 

 nerve, and the pleura; and on the left side, the remains of the thymus gland, the origin of the 

 left carotid artery, the left inferior thyroid vein, and the trachea. 



PLAN OF THE RELATIONS OF THE INNOMINATE ARTERY. 



In front. 

 Sternum. 



Sternohyoid and Sternothyroid muscles. 

 Remains of the thymus gland. 

 Left innominate and right inferior thyroid veins. 

 Inferior cervical cardiac branch from right vagus nerve. 



Right side. /" ^x Left side. 



Right innominate vein. / innominate \ Remains of thymus. 



Right vagus nerve. I Artery. ! L e ft carotid. 



Pleura. \ Left inferior thyroid vein. 



Trachea. 



Behind. 



Trachea. 

 Right pleura. 



Branches. The innominate usually gives off no branches, but occasionally a 

 small branch, the thyroidea ima, is given off from this vessel. It also sometimes 

 gives off a thymic or bronchial branch. 



The thyroidea ima (a. thyroidea ima), which is occasionally present, ascends in 

 front of the trachea to the lower part of the thyroid body, which it supplies. It 

 varies greatly in size, and appears to compensate for the deficiency or absence of 

 one of the other thyroid vessels. It occasionally is found to arise from the right 

 common carotid or from the aorta, the subclavian, or internal mammary vessels. 



of the cricoid cartilage to two inches below the upper border of the sternum. From this point 

 another incision, extending outward four inches in length to the junction (right) of the outer 



