Joint. A point where two bones meet is called a joint.
Joints are of two types :
(1) Fixed Joints or Immovable joints. The joints where the movement of the bones is not possible are called fixed or immovable joints. For example, upper jaw has fixed joint. The joints in the skull are fixed joints.
(2) Moveable joints. The joints where movement of the bones is possible are called moveable joints.
These are of four types
(a) Ball and Socket Joint. In this joint, a ball like rounded end of one bone fits into socket like cavity of the other bone. This joint allows the movement of the bones in all the directions. Joint between arm and shoulder is an example of this type of joint.
(b) Pivot Joint. In this type of joint, a cylinderical bone turns in a ring type bone. The cylinderical bone rotates inside the ring or the ring rotates outside the cylinder. The joint between skull and the vertebral column is an example of pivot joint. It allows the movement of head backward, forward, left and right.
(c) Hinge Joint. This joint is like hinge in the door. It allows movement of bones only in one direction i.e. up and down or front and back. Knee joint and elbow joint are the examples of the hinge joints.
(d) Gliding joint. This joint allows the bones to glide over each other providing only a little movement in all the direction. The examples of gliding joints are the joints between the ankle bones and wrist bones.
