The places in your body where two or more bones are joined together are called joints. Some joints are fixed, they do not move, and some joints are movable.
Fixed joints are found where one bone lies against another, sometimes with a thin layer of tissue separating them. Joints like these do not move at all, but the tissue is able to soften a hard blow you might receive and keep your bones from breaking. The joints of the bones in your skull are examples of fixed joints.
Movable joints are divided into three types, depending on their uses. There are hinge joints, pivot joints, and ball and socket joints.
Hinge joints allow the bones to move forward and backward, much like a door opens on its hinges. Hinge joints are found in your knee and fingers.
Pivot joints permit the bones to rotate, or turn around. When you move your head from side to side, or rotate your arm at the elbow, you are using pivot joints.
But the joints which give you the most movements are ball and socket joints. This is because of the way they are shaped. A long bone joins a shorter bone in this type of joint. The long bone has a large round end that fits into a hollowed-out curved section of the shorter bone, much like the way a ball would fit into the curled-up palm of your hand. Ball and socket joints give you the freedom of movement in your shoulders and hips.
Of the 22 bones connected by joints in your skull, only one can move, the one in your lower jaw, which permits you to talk, laugh, and chew food!