What are the 3 roots in sternocleidomastoid?

The sternocleidomastoid muscle has three roots: the sternal head, which originates from the manubrium of the sternum; the clavicular head, which arises from the medial portion of the clavicle; and the common tendon that connects these two heads to the mastoid process of the temporal bone and the superior nuchal line of the occipital bone. Together, these roots allow the muscle to perform functions such as head rotation and flexion.