Serratus posterior superior is a thin, quadrilateral muscle lying deep to the rhomboideus and superficial to the thoracolumbar fascia.

Proximal Attachment
It arises from the lower part of the ligamentum nuchae, the spinous processes of C7 to T3 and the intervening supraspinous ligaments.  

Distal Attachment
It descends infero-laterally ending in four digitations, which attach to the upper borders and external surfaces of the second to the fifth rib lateral to the angle.

Nerve Supply
Serratus posterior superior is supplied by the second to fifth intercostal nerves.

Action
Serratus posterior superior elevates the ribs.

For more information on the shoulder see ' The Interactive Shoulder'.