 Just above the level of the clavicle, the third portion of the subclavian artery curves lateralward and downward from the lateral margin of the scalenus anterior, across the first rib, to the axilla, and this is the situation most commonly chosen for ligaturing the vessel.Sometimes this vessel rises as high as 4 cm.above the clavicle; occasionally, it passes in front of the Scalenus anterior, or pierces the fibers of that muscle.