The exceptional flexibility of the shoulder girdle is due, in part, to the

The exceptional flexibility of the shoulder girdle is due, in part, to the ability of the scapula to slide easily against the thorax.
Because of that the following movements are possible:

Protraction: moving the scapula forwards, away from the spine.
Retraction:  opposite of protraction; scapula towards the spine.
Elevation: shoulder girdle to move upwards.
Depression: shoulder downwards.
Downward rotation: rotating the lower scapula towards the spine.