The subscapularis is a large triangular muscle. Supraspinatus , Infraspinatus , Subscapularis , and Teres Minor together This Four Muscle work as rotatory to the Humerus. So, also known as Rotator Cuff. ORIGIN: The subscapularis is originated from subscapular fossa of the scapula. INSERTION: The subscapularis is inserted at lesser tubercle of the humerus. ACTION: The subscapularis is chief medial rotator of the humerus, assisted by pectoralis major . The subscapularis is helped to hold the head of a humerus in glenoid cavity, stabilizes the shoulder. NERVE SUPPLY: The subscapularis is supplied by the Subcapular nerve.