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In human anatomy, the sternocleidomastoid muscle (), also known as sternomastoid and commonly abbreviated as SCM, is a paired muscle in the superficial layers of the side of the neck. It is one of the largest and most superficial cervical muscles. The primary actions of the muscle are rotation of the head to the opposite side and flexion of the neck. The sternocleidomastoid is innervated by the accessory nerve. It is given the name ''sternocleidomastoid'' because it originates at the manubrium of the sternum (''sterno-'') and the clavicle (''cleido-''), and has an insertion at the mastoid process of the temporal bone of the skull. ==Structure== The sternocleidomastoid originates from two locations, the manubrium of the sternum and the clavicle. It travels obliquely across the side of the neck and inserts at the mastoid process of the temporal bone of the skull. The sternocleidomastoid is thick and narrow at its centre, and broader and thinner at either end. The sternal head is a round fasciculus, tendinous in front, fleshy behind, arising from the upper part of the front of the manubrium sterni. It travels superiorly, laterally, and posteriorly. The clavicular head is composed of fleshy and aponeurotic fibers, arises from the upper, frontal 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Sternocleidomastoid muscle」の詳細全文を読む スポンサード リンク
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