The innominate artery is the first and widest of the three branches of the aorta, the others being the left common carotid artery and the left subclavian artery. The innominate artery begins opposite the center of the manubrium sterni, passes upward and to the right, and ends in the neck, behind the upper border of the right sternoclavicular joint, by dividing into the right common carotid and the right subclavian arteries. In the neck, it is separated from the right sternoclavicular joint, separated from it by the sternothyroid and sternohyoid muscles, and with the trachea medial, and the right innominate vein lateral to it. Behind it, there is a quantity of fat which separates it from the pleura; and in that fat the right vagus nerve descends obliquely to reach the trachea. As a rule it has no other branches, but occasionally a small artery, called the thyroidea ima, springs from it.
Relations of the innominate artery
Anterior to the innominate artery, there are the manubrium sterni, the right sternoclavicular joint, and the left innominate vein. The trachea is behind its lower part, but as the artery passes upward and to the right it gains the side of the trachea and has the upper part of the right lung and pleura behind it. The right innominate vein is on its right side and separates it from the right phrenic nerve and the pleura.