Sternocleidomastoid Muscle (SCM) Yeah, it's not an easy name😁 But if you figure out where this muscle is located, everything falls into place. It starts from the handle of the sternum and clavicle, and attaches to the mastoid process of the temporal bone. You can find it yourself by turning your head to the side and putting your hand on the opposite side of your neck - the SCM will be in a taut position. As you may have already recognized, this muscle is responsible for turning the head as well as keeping the head upright and flexing the spine in the cervical region.