Better known as the collarbone the clavicle is the bone in your chest that connects your breastbone to your shoulder and arm. It is a very superficial bone, and injuries are typically quite common to see.
The clavicle is surrounded by a number of muscles and important structures. The muscles of the shoulder, including the deltoid and trapezius surround the clavicle on the outside and behind it respectively. There are also important structures that connect the clavicle bone to another bone, the coracoid. These are the conoid and trapezoid ligaments. These are important in fractures at the end of the collarbone as well as an injury know as an AC separation.
Underneath the clavicle there are important blood vessels that supply the rest of the upper body. The lungs are also below the collarbone.
Fractures to this bone are quite common because it is very superficial. Typically, these fractures occur after a fall off a bicycle or a similar mechanism. Often times, especially in younger children, these fractures heal in a few weeks with the use of a sling. In adolescents, if the bones are separated quite far from each other, your physician may recommend surgery to bring the fracture in closer alignment.
Here is the xray of a broken clavicle in an adolescent female after she fell off of a horse. Since the bones are very far apart from each other, the decision was made to surgically fix this bone. The xray on the bottom demonstrates the clavicle bone after surgery. There is a screw in the middle holding the middle fragment in place, and then the plate and screws on top.