The anterior sternoclavicular ligament is a broad band of fibers, covering the anterior surface of the articulation; it is attached above to the upper and front part of the sternal end of the clavicle

Clavicle

In human anatomy, the clavicle or collar bone is a long bone of short length that serves as a strut between the scapula and the sternum. It is the only long bone in body that lies horizontally...

, and, passing obliquely downward and medialward, is attached below to the front of the upper part of the manubrium sterni.

This ligament is covered by the sternal portion of the Sternocleidomastoideus and the integument; behind, it is in relation with the capsule, the articular disk, and the two synovial membranes.