The shoulder joint consists of 2 bones, the Scapula and the Humerus. The scapula has several parts. The blade of the scapula is what can be felt as the shoulder blade. This provides a surface for the attachment of many muscles. The acromion is a continuation of a thickening of the blade called the spine of the scapula. The acromion lies over the top of the shoulder joint, covering the rotator cuff muscles. Part of the deltoid muscle takes its origin from this bone. The acromion forms a joint with the clavicle (collar bone) at the front of the shoulder (the acromio-clavicular joint). A small protrusion of the scapula forwards is the coracoid and this has the origin of part of the biceps muscle. The final part of the scapula id the glenoid. This is a flattened area in facing outwards and serves as the articulating or joint surface with the humerus.
The humerus has the long shaft of the upper arm and ends with the humeral head, which articulates with the glenoid. There is a groove for the long head of the biceps muscle and tuberosities (bumps) for the attachment of the rotator cuff muscles.