The left brachial artery is a branch of the common brachiocephalic trunk while the right is a branch of the brachiocephalic artery.
Each brachial artery after its origin is directed forwards between the layers of the anterior mediastinum and the trachea towards the thoracic inlet.
They reach the medial face of the first rib, the left one arising to the side of the trachea and the right passing nearly on the median line and under the trachea to the left and above the anterior vena cava.
Each artery leaves the thoracic cavity by winding round the anterior border of the first rib below the insertion of scalenus ventralis and above the brachial veins to reach the axilla, thus leaving an impression on the rib.
It then bends downward, in the axilla. In the midst of the branches of the brachial plexus of nerves, gets included in the loop formed between the musculocutaneous and median nerve on the medial face of shoulder joint, places itself across the subscapularis and turns distally on the medial surface of the arm.
In the axillary part of the course the artery is related to the serratus thoracis and rectus thoracis, medially.
It at first curves slightly forwards, then descends in an almost vertical direction crossing the shaft of the humerus obliquely and reaches the lower extremity of the bone, below its medial condyle it is continued as the median artery.
In its course downwards, it rests successively on teres major, medial head of triceps and the humerus.
It is related anteriorly to the coracobrachialis above and the biceps below. The median nerve is directly in front and in contact, separating the muscle and this vessel.
Behind the artery is the brachial vein and further behind is the ulnar nerve. It gives off a number of collateral branches both inside and outside the thoracic cavity.
