Infraspinatus muscle

Structure It attaches medially to the infraspinous fossa of the scapula and laterally to the middle facet of the greater tubercle of the humerus. The muscle arises by fleshy fibers from the medial two-thirds of the infraspinatous fossa, 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 teres major and teres minor. Relations 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. Innervation The suprascapular nerve innervates the supraspinatus and infraspinatus muscles. These muscles function to abduct and laterally rotate the arm, respectively. Variation The infraspinatus is frequently fused with the teres minor. ==Function==

The infraspinatus is the main external rotator of the shoulder. When the arm is fixed, it adducts the inferior angle of the scapula. Its synergists are teres minor and the deltoid. The infraspinatus and teres minor rotate the head of the humerus outward (external, or lateral, rotation); they also assist in carrying the arm backward. ==In other mammals==

The pectoral muscles – the pectoralis major and pectoralis minor – are thought to have evolved from a primitive muscle sheet that connected the coracoid to the humerus. In late reptilians and early mammals, this muscle structure was displaced dorsally; while most of its components evolved into the pectoralis major, some fibers eventually attached to the scapula and evolved into the supraspinatus, the infraspinatus, and parts of the subscapularis. == Meat ==

In butchery, the infraspinatus of cattle forms the top blade subprimal, part of the shoulder clod. The large, tough, and chewy sheet or seam of gristle that runs down the middle is the shoulder tendon. Used whole, the infraspinatus is a top blade roast; cut perpendicularly, it gives top blade steaks; filleted into two long, flat cuts by seam cutting along the tendon then portioned, it gives flat iron steak. ==Additional images==