Trapezius muscle

Origin: Down the midline, from the external occipital protuberance, the nuchal ligament, the medial part of the superior nuchal line, and the spinous processes of the vertebrae C7-T12

Insertion: At the shoulders, into the lateral third of the clavicle, the acromion process and into the spine of the scapula

Artery: Transverse cervical artery

Nerve: Major nerve supply is the cranial nerve XI. Cervical nerves C3 and C4 receive information about pain in this muscle

Action: Descending (superior) part elevates; ascending (inferior) part depresses; and middle part (or all parts together) retracts scapula; descending and ascending parts act together to rotate glenoid cavity superiorly

Antagonist: Serratus anterior muscle

Description:
The Trapezius is a flat, triangular muscle, covering the upper and back part of the neck and shoulders. It arises from the external occipital protuberance and the medial third of the superior nuchal line of the occipital bone, from the ligamentum nuchae, the spinous process of the seventh cervical, and the spinous processes of all the thoracic vertebrae, and from the corresponding portion of the supraspinal ligament. From this origin, the superior fibers proceed downward and lateralward, the inferior upward and lateralward, and the middle horizontally; the superior fibers are inserted into the posterior border of the lateral third of the clavicle; the middle fibers into the medial margin of the acromion, and into the superior lip of the posterior border of the spine of the scapula; the inferior fibers converge near the scapula, and end in an aponeurosis, which glides over the smooth triangular surface on the medial end of the spine, to be inserted into a tubercle at the apex of this smooth triangular surface. At its occipital origin, the Trapezius is connected to the bone by a thin fibrous lamina, firmly adherent to the skin. At the middle it is connected to the spinous processes by a broad semi-elliptical aponeurosis, which reaches from the sixth cervical to the third thoracic vertebrae, and forms, with that of the opposite muscle, a tendinous ellipse. The rest of the muscle arises by numerous short tendinous fibers. The two Trapezius muscles together resemble a trapezium, or diamond-shaped quadrangle: two angles corresponding to the shoulders; a third to the occipital protuberance; and the fourth to the spinous process of the twelfth thoracic vertebra.
Variations.—The attachments to the dorsal vertebrae are often reduced and the lower ones are often wanting; the occipital attachment is often wanting; separation between cervical and dorsal portions is frequent. Extensive deficiencies and complete absence occur.
The clavicular insertion of this muscle varies in extent; it sometimes reaches as far as the middle of the clavicle, and occasionally may blend with the posterior edge of the Sternocleidomastoideus, or overlap it.