Origin: Manubrium sterni, medial portion of the clavicle
Insertion: Mastoid process of the temporal bone, superior nuchal line
Artery: Occipital artery and superior thyroid artery
Action: Acting alone, tilts head to its own side and rotates it so the face is turned towards the opposite side. Acting together, flexes the neck, raises the sternum and assists in forced inspiration.
The Sternocleidomastoideus (Sternomastoid muscle) passes obliquely across the side of the neck. It is thick and narrow at its central part, but broader and thinner at either end.
It arises from the sternum and clavicle by two heads:
The two heads are separated from one another at their origins by a triangular interval, but gradually blend, below the middle of the neck, into a thick, rounded muscle which is inserted, by a strong tendon, into the lateral surface of the mastoid process, from its apex to its superior border, and by a thin aponeurosis into the lateral half of the superior nuchal line of the occipital bone.