Anatomy of the Shoulder
What it is
The shoulder is made up of three bones:
These bones are joined together by soft tissues (ligaments, tendons, muscles, and joint capsule) to form a platform for the arm to work. The shoulder is made up of three joints:
The shoulder also has one articulation, which is the relationship between the scapula (shoulder blade) and the chest wall. The main joint of the shoulder is the glenohumeral joint. This joint comprises a ball (the humeral head) on a golf-tee-shaped joint (the glenoid of the scapula).
The bones of the shoulder are covered by several layers of soft tissues.
The top layer is the deltoid muscle, a muscle just beneath the skin, which gives the shoulder a rounded appearance. The deltoid muscle helps to bring the arm overhead. Directly beneath the deltoid muscle is sub-deltoid bursa, a fluid-filled sac, analogous to a water balloon.
Source from AAOS, Viewmedica, WebMD