The scalenus anterior is an important muscle that takes origin from the transverse processes of the third, fourth, fifth, and sixth cervical vertebrae, and descends, tapering, to be inserted into the first rib. It lies in front of the cervical pleura, and crosses in front of the subclavian artery (second part). It is concealed by the sternomastoid. The phrenic nerve descends over the front of the muscle; it lies between the muscle and its fascia, and crosses the muscle gradually from lateral to medial border. Superficial to that, the muscle is crossed by the inferior belly of the omohyoid, the transverse cervical artery, the suprascapular artery, the anterior jugular vein, and the subclavian vein – named in order from above downwards. The anterior primary rami of the cervical nerves, from the fourth downwards, emerge at the lateral border of the muscle.