Origin: Infraspinatus Fossa (16) and Spine of the Scapula (10) 
Insertion: medial Facet of the Greater Tubercle of the Humerus (7)
Actions: Lateral Rotation of the arm, assists the shoulder Extension and stabilizes Humeral head in the Glenoid Cavity
Helping Synergist Muscles:
- Supraspinatus (2), Teres Minor (4), Deltoid (1) (just posterior fibers)
Notes: the Infraspinatus is a thick triangular muscle that joins to form the "Rotator Cuff Muscles" together with Supraspinatus, Subscapularis and Teres Minor