[TA] intrinsic (scapulohumeral) muscle of shoulder joint, the tendon of which contributes to the formation of the rotator cuff; origin, infraspinous fossa of scapula; insertion, middle facet of greater tubercle of humerus; action, extends arm and rotates it laterally; its tonic contraction helps to hold the head of the humerus in the shallow glenoid fossa; nerve supply, suprascapular (from fifth to sixth cervical spinal nerves). SYN: musculus infraspinatus [TA].