Cervical Spine Neck Muscles Sterno-cleido-mastoid physical therapy illustrations. Shows anterior and lateral views during sternocleidomastoid contraction and relaxation. Sternocleidomastoid’s sternal or medial head originates from the upper part of the anterior surface of the manubrium sterni. Sternocleidomastoid’s clavicular or lateral head originates from the superior surface of the medial third of the clavicle. See the attached physical therapy illustrations. Sternocleidomastoid inserts onto the lateral surface of the mastoid process from its apex to its superior border, and to the lateral half of the superior nuchal line by a thin aponeurosis. Sternocleidomastoid is innervated by the accessory nerve and branches from the ventral rami of C2, C3 and C4 spinal nerves. Visit http:/www.medilaw.tv for more information. Cervical Spine Neck Muscles Sterno-cleido-mastoid physical therapy illustrations.