A two-headed muscle deep on the anterolateral surface of the neck. The muscle has one of its origins on the manubrium of the sternum and the other on the medial aspect of the clavicle; its insertion is on the mastoid process (a nipple-like extension) of the temporal bone. The primary actions of the sternocleidomastoid are flexion of the neck, extension of the head, and lateral flexion about the spine. It also acts as an accessory inspiratory muscle, elevating the sternum.
Subjects: Sports and Exercise Medicine.