Sternocleidomastoid

[Renato]

In human anatomy, the sternocleidomastoid 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.
It is given the name sternocleidomastoid because it originates at the manubrium of the sternum and the [clavicle], and has an insertion at the [mastoid] process of the [temporal] bone of the skull.