In
human anatomy, the
sternocleidomastoid muscle (), also known as
sternomastoid and commonly abbreviated as
SCM, is a paired muscle in the
superficial layers of the side of the
neck. It is one of the largest and most superficial cervical muscles. The primary actions of the muscle are rotation of the head to the opposite side and
flexion of the neck. The sternocleidomastoid is innervated by the
accessory nerve.