_Insertion._—The body of the hyoid bone, in common with the hyoid branch of the preceding muscle. _Action._—To depress the hyoid bone. _Structure._—The muscle is composed of parallel fleshy fibers, except at its origin, where it has a thin tendon. _Relations._—In the first part of its course the muscle passes forward between the supraspinatus, anterior deep pectoral, mastoido-humeralis (outwardly), and the scalenus (inwardly). It is intimately adherent to the mastoido-humeralis. In the middle of the neck it is related superficially to the mastoido-humeralis, sterno-cephalicus, and the jugular vein; deeply, to the rectus capitis anterior major, the carotid artery, the vagus, sympathetic, and recurrent nerves, the trachea, and, on the left side, the œsophagus. In its anterior part the muscle blends with the hyoid part of the sterno-thyro-hyoideus, the two covering the thyroid portion of the latter muscle, the thyroid gland, and the ventral face of the larynx. _Blood-supply._—Carotid and inferior cervical arteries. _Nerve-supply._—Ventral branches of the cervical nerves. 6. =Scalenus= (M. scalenus primæ costæ).—This muscle is deeply situated on the side of the posterior half of the neck. It is composed of two parts, between which the roots of the brachial plexus of nerves emerge. _Origin._—The anterior border and outer surface of the first rib. _Insertion._—(1) The dorsal (smaller) portion is attached to the transverse process of the seventh cervical vertebra; (2) the ventral portion is attached to the transverse processes of the sixth, fifth, and fourth cervical vertebræ. _Action._—The neck is flexed or inclined laterally, according as the muscles act together or singly. If the neck be the fixed point, the muscle may have a respiratory action by pulling forward or fixing the first rib. _Structure._—The dorsal portion is composed of three or four fleshy bundles.[43] The ventral portion, which is much larger, is almost entirely fleshy, and not so divided. _Relations._—Superficially, the anterior deep pectoral, mastoido-humeralis, and omo-hyoideus muscles, the phrenic nerve, and the other branches of the brachial plexus; deeply, the vertebræ, the longus colli and intertransversales muscles, the œsophagus (on the left side), the trachea (on the right side), the vertebral vessels, the vagus, sympathetic, and recurrent nerves. The roots of the brachial plexus form a flat anastomosis, which lies between the two portions of the muscle. The brachial vessels cross the ventral edge close to the first rib. _Blood-supply._—Carotid, vertebral, and inferior cervical arteries. _Nerve-supply._—Ventral branches of the cervical nerves. 7. =Rectus capitis anterior major= (M. longus capitis).—This is the largest of the three special flexors of the head, and lies along the ventro-lateral surface of the anterior cervical vertebræ and the base of the cranium. _Origin._—The transverse processes of the fifth, fourth, and third cervical vertebræ.