The Shoulder Girdle

The shoulder girdle, also called the pectoral girdle, is made up of four bones.  They are:  the clavicles (left and right) and the scapulae (left and right).

The Clavicles
The clavicle is the bone in the shoulder girdle that is often referred to as the collarbone.  It is a curved bone that connects the upper extremity (arm) to the body (the trunk), and provides several attachment sites for muscles and ligaments.  The clavicle is unique in that a portion of this bone is not covered by muscle, but only covered by skin.  Because of this difference, it is oven visible on many people.  The clavicle's primary purpose is to maintain distance between the upper extremity and trunk to allow the shoulder to move freely.

The Scapulae
The scapula is the bone in the shoulder that is often referred to as the shoulder blade (because of its blade-like appearance).  The primary purpose of the scapula is to connect the humerus (upper arm bone) to the clavicle (collar bone).  The scapula forms the back portion of the shoulder girdle and has several ridges on the front and back that allow muscles, tendons and ligaments to attach.  Below is a diagram that shows the clavicles and the scapulae. 
