The Sternocleidomastoid is the primary landmark in the neck. It shares its innervation (CN XI spinal accessory) with the trapezius. The sternocleidomastoid points the chin to the opposite side of the contracting muscle. It draws the head to the shoulder on the same of the contracting muscle.

The clinical condition associated with an injury (ischemia, contraction from tearing, congenital shortening) to the sternocleidomastoid is wryneck. Wryneck is a flexion deformity of the neck. The head is drawn toward and rotated away from the side of the deformity.