The Collar Bone

The Shoulder joint (also known as the pectoral or shoulder girdle) is made up of three bones: the clavicle(collarbone); the scapula and the head of the humerus.

The Clavicle (or collar bone)

The clavicle is an S-shaped bone and is the main connection between the upper arm and the rest of the axial skeleton. The bone runs along the front of the shoulder to the breast bone (sternum). It is the only long bone in the human body that lies horizontally.

The clavicle is also an important site for muscle attachments including:

Pectoralis Major
Trapezius
Sternoclaedomastoid
Sternohyoid
Subclavius

The Function of the Collar Bone

The Clavicle allows the scapula to move freely on the thoracic wall due to the way in which it acts as a rigid support for the scapula and the arm. This gives the arm a higher range of movement.
The collar bone protects the neurovascular bundle that supplies the upper limb.
The Clavicle acts as a shock absorber by transmitting physical impacts from the upper limb to the axial skeleton.