The subclan vein forms an arch across the pleura at a level below the arch of subclan aery. The two arches are separated from each other by scalenus anterior muscle.Scalenus anterior arises from the anterior tubercles of C3-C6 and attaches to the scalene tubercle and adjacent ridge on the inner border and upper surface of the first rib.Phrenic nerve passes veically down across the obliquity of the muscle, plastered there to by the preveebral fascia.Transcervical and suprascapular aeries lie between the scalenus anterior and the carotid sheath.