Origin and Insertion
The sternocleidomastoid passes obliquely across the side of the neck.
It is thick and narrow at its central part, but broader and thinner at either end.
- The medial or sternal head is a rounded fasciculus, tendinous in front, fleshy behind, which arises from the upper part of the anterior surface of the manubrium sterni, and is directed superiorly, laterally, and posteriorly.
- The lateral or clavicular head, composed of fleshy and aponeurotic fibers, arises from the superior border and anterior surface of the medial third of the clavicle; it is directed almost vertically upward.
The two heads are separated from one another at their origins by a triangular interval (supraclavicular fossa) 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. The function of this muscle is to rotate the head to the opposite side or obliquely rotate the head. It also flexes the neck.
Read more about this topic: Sternocleidomastoid Muscle
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