Lateral Vertebral Muscles
| Scalenus anterior | Scalenus posterior |
| Scalenus medius | |
The Scalenus anterior lies deeply at the side of the neck, behind the Sternocleidomastoid muscle. It arises from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical vertebrae, and descending, almost vertically, is inserted by a narrow, flat tendon into the scalene tubercle on the inner border of the first rib, and into the ridge on the upper surface of the rib in front of the groove for the subclavian artery.
Relations.--In front of it are the, clavicle, the Subclavius. Sternocleidomastoid, and Omohyoid muscles, the lateral portion of the carotid sheath, the transverse cervical, suprascapular and ascending cervical arteries, the subclavian vein, the prevertebral fascia and the phrenic nerve. Its posterior surface is in relation with the pleura, and with the nerves forming the brachial plexus and the subclavian artery, which separate it from the Scalenus medius. Below, it is separated from the Longus cervicis by an angular interval (fig. 593), in which the vertebral artery, with its companion vein on its lateral side, ascends to reach the foramen transversarium of the sixth cervical vertebra. The inferior thyroid artery crosses the interval from the lateral to the medial side near its apex. The sympathetic trunk and its inferior cervical ganglion are closely related to the medial side of this part, of the vertebral artery. On the left side the thoracic duct crosses this interval at the level of the seventh cervical vertebra and usually comes into contact with the medial edge of the muscle. Above, it is separated from the Longus capitis by the ascending cervical branch of the inferior thyroid artery.
Figure 593
Nerve-supply.-The Scalenus anterior is supplied by branches from the anterior primary rami of the fourth, fifth, and sixth cervical nerves.
Actions.-Acting from below the Scalenus anterior bends the cervical portion of the vertebral column forwards and laterally and rotates it towards the opposite side. When the muscle acts from above it assists in elevating the thorax.
The Scalenus medius, the largest and longest of the Scaleni, arises from the front of the posterior tubercles of the transverse processes of the lower six cervical vertebra, and frequently extends upwards to the transverse process of the atlas (fig. 592); it is inserted into the upper surface of the first rib, between the tubercle of the rib and the groove for the subclavian artery.
Relations.-Its anterolaleral surface is in relation with the Sternocleidomastoid; it is crossed by the clavicle and the Omohyoid : anteriorly, it is separated from the Scalenus anterior by the subclavian artery and the cervical nerves. The Levator scapulae and the Scalenus posterior are posterolateral to it. The upper two roots of the nerve to Serratus anterior (long thoracic nerve), and the nerve to the Rhomboids (dorsal scapular nerve) pierce the substance of the muscle and appear on its lateral aspect.
Nerve-supply.-The Scalenus medius is supplied by branches from the anterior primary rami of the cervical nerves.
Actions.-The Scalenus medius, acting from below, bends the cervical part of the vertebral column laterally; acting from above it helps to raise the thorax.
The Scalenus posterior, the smallest and deepest of the Scaleni, arises from the posterior tubercles of the transverse processes of the fourth, fifth, and sixth cervical vertebrae, and is inserted by a thin tendon into the outer surface of the second rib, behind the tubercle for the Serratus Inferior. It is occasionally blended with the Scalenus medics.
Nerve-supply.-The Scalenus posterior is supplied by branches from the anterior primary rami of the lower three cervical nerves.
Actions.--The Scalenus posterior bends the lower end of the cervical part of the vertebral column laterally, when the second rib is fixed; if its upper attachment be fixed it helps to elevate the thorax.
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Vertebral Column