The muscles of the shoulder either connect the scapula and clavicle to the trunk, or connect the clavicle, scapula and body wall to the proximal (top) end of the humerus. The trapezius, levator scapulae, and rhomboids originate from the base of the skull and/or spine and connect the scapula and clavicle to the trunk of the body. The pectoralis major, pectoralis minor, latissimus dorsi, teres major and deltoid connect to the proximal end of the humerus and anchor it to the body.
The most important shoulder muscles are the four rotator cuff muscles - the subscapularis, supraspinatus, infraspinatus and teres minor muscles - which connect the scapula to the humerus and provide support for the glenohumeral joint.
Muscles of the arm that enter into the shoulder complex are separated into anterior (flexor) and posterior (extensor) compartments. These include biceps brachii, triceps brachii and coracobrachialis.
These shoulder muscles can be separated into three important groups: