The human clavicle, or collarbone, has six muscles directly attached to it. At the front top are attached the trapezius and sternocleidomastoid muscles. At the bottom front and back are attached the deltoid and pectoralis major. To the inside is the subclavius. At the inside top is the sternohyoid. Finally, at the inside bottom opposite the sternohyoid are the trapezoid and coracoclavicular ligaments. Because there are two clavicles, there are a total of ten muscles attached to them.
The trapezius muscle is a large muscle near the surface of the body. It occurs on the back and is connected at one end to the spine along the full length of the neck and chest and to the shoulder at the other end. This muscle also wraps over the part of the body between the shoulder joint and the neck and connects to the top of the clavicle. There are two trapezius muscles in the human body, one on each side of the spine and connected to each clavicle.
The sternocleidomastoid muscle is a short, diagonal muscle that runs from the top of the clavicle to the back of the head just behind the ears. It lies just below the skin and is usually visible in a person’s bare neck. The connection to the clavicle is near the central portion of the clavicle close to the sternum, or breastbone. There are, again, two sternocleidomastoid muscles, one on each side of the body.
The deltoid muscle wraps around the entire shoulder area from front to back and neck to upper arm. It gives the human shoulder its distinctive shape, especially when well developed. At the back it attaches to the scapula, or shoulder blade. At the front it attaches to the underside of the clavicle, partly wrapping around the clavicle to attach both to the front of it and the part closer to the inside of the body. There are two deltoid muscles, one left and one right.
The pectoralis major muscle is the large muscle that covers most of the chest. It gives the male chest its distinctive square shape, especially when well developed. It is attached to both the shoulder and sternum. To the clavicle, it attaches along much of the underside, wrapping around much as the deltoid muscle does. There are two pectoralis major muscles symmetrically in the human body.
The subclavius is a small horizontal muscle that runs just under the clavicle for its full length, filling the space between the clavicle and the top rib. Its top end extends underneath the clavicle and attaches halfway up its underside near the longitudinal middle. There are two subclavius muscles, one per clavicle.
The sternoclavicular muscle is a short vertical muscle that connects the top of the clavicle to the hyoid bone, or adam’s apple. There are two of them, one per clavicle and attached to each side of the hyoid.
Each human clavicle also has two main ligaments attached to it, the trapezoid and conoid, as well as the costoclavicular tissue.