Subclavius muscle

At a glance

English

Subclavius muscle

Latin (TA2)

Musculus subclavius

System

Muscle

Region

Trunk

Side

Paired, left and right

About the subclavius muscle

Subclavius lies in the narrow space between the collarbone and the first rib, hidden under pectoralis major and wrapped in the clavipectoral fascia. Together with the two pectoral muscles, it belongs to the anterior group of muscles that tie the upper limb to the front of the trunk and frame the front wall of the axilla.

It begins by a short, stout tendon from the first rib where the rib joins its cartilage, just anterior to the costoclavicular ligament. Its fleshy belly then runs outward and upward, roughly parallel to the clavicle, and attaches into a groove under the middle third of the bone, the subclavian groove. Variations are uncommon but include an attachment to the coracoid process instead of, or as well as, the clavicle, and rarely the muscle is missing.

The muscle pulls the clavicle downward and forward and, more importantly, presses its inner end into the sternoclavicular joint, steadying the collarbone while the shoulder girdle moves. When the clavicle is fixed it may lift the first rib slightly. Its nerve, the nerve to subclavius, is a small branch from the brachial plexus, off its upper trunk, carrying fibres from spinal segments C5 and C6; it sometimes gives an accessory phrenic nerve. Blood reaches the muscle from the clavicular branch of the thoracoacromial artery and from the suprascapular artery.

Subclavius sits directly above the subclavian vessels and the brachial plexus as they cross the first rib. When the clavicle breaks, which it does often, the muscle acts as a cushion that helps to shield these structures from the broken bone ends. In the narrow costoclavicular space, however, a bulky or tight subclavius can add to compression of the vessels and nerves, one of the mechanisms behind thoracic outlet syndrome.

Attachments, action and supply

Origin

First rib and its costal cartilage at their junction.

Insertion

Subclavian groove beneath the middle third of the clavicle.

Action

Depresses the clavicle and anchors it against the sternum, steadying it during shoulder movement; may raise the first rib.

Nerve supply

Nerve to subclavius (C5, C6), a branch of the upper trunk of the plexus.

Blood supply

Clavicular branch of the thoracoacromial artery and the suprascapular artery.