the ball and socket joint (or spheroidal joint) is a joint in which the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. The distal bone is capable of motion around an indefinite number of axes, which have one common center. It enables the bone to move in many planes (almost all directions).
An enarthrosis is a special kind of spheroidal joint in which the socket covers the sphere beyond its equator.
Examples of this form of articulation are found in the hip, where the rounded head of the femur (ball) rests in the cup-like acetabulum (socket) of the pelvis, and in the glenohumeral joint of the shoulder, where the rounded head of the humerus (ball) rests in the cup-like glenoid fossa (socket) of the shoulder blade. It should be noted that the shoulder includes a Sternoclavicular articulation joint.
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This article incorporates text from a public domain edition of Gray's Anatomy.