Subscapularis

One of the 4 muscles of the rotator cuff, the subscapularis originates from the subscapular fossa on the anterior aspect of the scapula and inserts into the lesser tubercle of the humerus.  It is innervated by the upper and lower subscapular nn.  In addition to stabilizing the glenohumeral joint, the subscapularis also internally rotates the humerus.