Muscular (deep) branches of the cervical plexus distribute to several groups of muscles. A major branch is the phrenic nerve, which supplies the diaphragm with both sensory and motor innervation (Fig. 8.188). It arises from the anterior rami of cervical nerves C3 to C5. Hooking around the upper lateral border of the anterior scalene muscle, the nerve continues inferiorly across the anterior surface of the anterior scalene within the prevertebral fascia to enter the thorax (Fig. 8.189). As the nerve descends in the neck, it is “pinned” to the anterior scalene muscle by the transverse cervical and suprascapular arteries.