Subclavius muscle

The subclavius muscle is a muscle of the shoulder located under the clavicle (collarbone) that depressed the clavicle to stabilize it during shoulder movements.

Origin
The subclavius originates from the first rib. Specifically, it attaches at the costochondral junction of the first rib.

Insertion
The subclavius muscle inserts at the clavicle, at the subclavian groove on lower surface of the middle third of the clavicle.