The subscapularis is a large triangular muscle which fills the subscapular fossa and inserts into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint, 1899. From 'The Treatise of the Human Anatomy and Its Applications to the Practice of Medicine and Surgery, Volume I' (1899). It arises from its medial two-thirds and from the lower two-thirds of the groove on the axillary border (subscapular fossa) of the scapula. (Photo by VintageMedStock/Getty Images)

The subscapularis is a large triangular muscle which fills the subscapular fossa and inserts into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint, 1899. From 'The Treatise of the Human Anatomy and Its Applications to the Practice of Medicine and Surgery, Volume I' (1899). It arises from its medial two-thirds and from the lower two-thirds of the groove on the axillary border (subscapular fossa) of the scapula. (Photo by VintageMedStock/Getty Images)