At the top of the "thorax" is the shoulder girdle. This is made of two thin horizontal bones at the front, joined to the "sternum". These two bones are called the clavicles or "collar bones". At the back of the "thorax" are two flat triangular-shaped bones called the scapulae, or "shoulder blades". The "clavicles" and "scapulae" come together on each side to make "shoulders". The bones of the arms fit into sockets (cup-like holes) in the "scapulae". 