One of the most mobile and intricate joints in the body, the shoulder joint represents much more. With its ball and socket design, the arm bone has a chalice-like cup to rest into and express from. The humerus arm bone can move around many axises in nearly all directions. The shoulder joint allows for movement of the shoulder girdle: up, down, inward, outward, and circular. http://www.nianow.com/story/2013/03/awareness-of-shoulder-joint-sensing-freedom