A: Humerus
B: Scapula
C: Clavicle

Synovial joint: Ball and socket
because the head of the humerus fits into the socket (glenoid cavity) of the scapula. You can see the articular shapes of the two bones clearly in these two X-rays. This joint is one of the most freely moving of all synovial joints. The movements are allowed in all axes and planes: flexion/extension, adduction/abduction, circumduction and rotation. This freedom of movements is typical of the "Ball and Socket" subtype.