Joints and Ligaments
The skeleton, you have seen, consists of over two hundred bones. Nearly every bone is joined to
another bone in one way or another. The place where two bones meet is called a joint. As you
can imagine, the body has several different kinds of joints. It has special kinds of joints that
allow no movement, such as the joints in the cranium. It has other kinds of joints that allow only
limited movement, such as the joints in the spinal column. It has other kinds of joints that allow
free movement of varying 172 degrees, such as the joints in the shoulders and the joints in the
Suture joints. In some parts of the skeleton two bones come together to form a firm,
immovable structure. Such is the case in the cranium, where there is need for a rigid structure to
protect the brain. Such joints are called suture (sti'char) joints. Look at the illustration of the
joints. Joints in the spinal column. The bones in the spinal column, of course, require a joint
quite different from the bones in the cranium.
The joints must be rigid enough to enable the spinal column to support the upper part of
the body. At the same time, they must allow a certain amount of movement in many directions
for twisting, turning, and bending. In the illustration you can see the principal kind of joint found
in the spinal column. The joint consists of a disk of cartilage (kar'ta lij), a tough, elastic,
semirigid material that allows a limited amount of movement at the same time it gives support.
Hinge joints. Think of what happens when a door moves on a hinge. The door moves
back and forth in one plane. Hinge joints are joints that permit the bones in the body to move
back and forth in one plane
Pivot joints. You know that there is a hinge joint in the elbow. There is another kind of
joint near the elbow. Put your elbow, forearm, and hand on your desk, palm down. Without
raising your arm, turn your hand over, palm up. Do you see how the arm rolls over almost com-
pletely at the wrist but only slightly at the elbow? This is because the radius is attached to the
humerus with a pivot joint.
Ball-and-socket joints. Keep your arm stiff and move it about the shoulder. Can you
move it in practically any direction? This is because the arm is connected to the shoulder by a
ball-and-socket joint. What other part of the skeleton besides the shoulder has a ball-and-socket
joint? Does the ball-and-socket joint in the hip give as much freedom of movement as the one in
Lubricants. What happens when you rub two sticks together? They become hot and begin
to wear because of friction, don't they? How can you prevent the wear caused when two objects
rub together constantly? You can make the areas that touch as smooth as possible, and you can
use some kind of lubricant.
Do you think the movable joints of the skeleton need protection against wear, too? They do. How
are they protected? First, all moving parts in every joint are coated with a smooth jacket of
cartilage. Second taking place in your body. You may feel confused about yourself and others At
such times you should be patient. You should realize that your emotions will catch up with the
rest of you. You can make this easier by cultivating attitudes that aid your emotional growth. In
this way you can set yourself free to be the man or woman you want to be.