Answer: Each of a pair of long muscles that connect the sternum, clavicle, and mastoid process of the temporal bone and serve to turn and nod the head is called STERNOCLEIDOMASTOID (SCM) MUSCLE.
Explanation: The name was derived from the fact that the muscle is attached to three bones; manubrium of sternum, clavicle and mastoid process of temporal bone.
When you tilt your neck to either left or right, Sternocleidomastoid muscle is located at the side of the neck which functions as an important landmark dividing the sides of the neck into two triangles.