Infraspinatus - Musculus infraspinatus
Origin: Infraspinous fossa of thescapula
Insertion: Middle facet of greater tubercle of the humerus
Artery: Suprascapular and circumflex scapular arteries
Nerve: Suprascapular nerve
Action: Lateral rotation of arm and Adduction of arm and stabilizeshumerus
Antagonist: Subscapularis, pectoralis major, and latissimus dorsi
The Infraspinatus is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa; it arises by fleshy fibers from its medial two-thirds, and by tendinous fibers from the ridges on its surface; it also arises from the infraspinatous fascia which covers it, and separates it from the Teretes major and minor. The fibers converge to a tendon, which glides over the lateral border of the spine of the scapula, and, passing across the posterior part of the capsule of the shoulder-joint, is inserted into the middle impression on the greater tubercle of the humerus. The tendon of this muscle is sometimes separated from the capsule of the shoulder-joint by a bursa, which may communicate with the joint cavity.
This definition incorporates text from a public domain edition of Gray's Anatomy (20th U.S. edition of Gray's Anatomy of the Human Body, published in 1918 – from http://www.bartleby.com/107/).