Origin: Infraspinous process of the scapula Insertion: Middle part of the greater tubercle of the humerus

Action: Laterally rotates arm at shoulder.  Stabilizes shoulder by drawing the humerus towards the glenoid fossa of the scapula.  Also part of the "STIS" muscle group which is commonly known as the rotator cuff (musculotendinous) muscles that enforce joint security around the head of the humerus