1. Skeletal System
The skeletal system or skeleton contains bones which form a framework inside your body.

3. What Are Bones Made Of?
If you've ever seen a real skeleton or fossil in a museum, you might think that all bones are dead. Although bones in museums are dry, hard, or crumbly, the bones in your body are different. The bones that make up your skeleton are all very much alive, growing and changing all the time like other parts of your body.

4. What are bones made of? The hard outside layer is called compact bone.
Tiny blood vessels go into the compact bone.
The blood brings nutrients and certain other things to the living bone cells.

5. What are bones made of?
The knoblike part at the end of the bone is filled with spongy bone.
It is called spongy bone because it is filled with holes, like a sponge. But it is not soft like a sponge.
Spongy bone is made of many hard, crisscrossing tubes. All the holes help make the bone light without making it weak.

6. What are bones made of?
The spaces in spongy bones are full of blood vessels and a soft tissue called marrow.
The marrow in spongy bone is red.
It makes and repairs the hard parts of the bone.
It also builds the cells that make your blood red.

7. Long Bones The long, tube-like part of the bones is called the shaft.
Long bones are light because their shafts are hollow.
The hollow space also contains marrow, but this marrow is yellow.
Yellow marrow helps build the long part of the bone.

8. Flat Bones
Flat bones, such as your ribs, have an outer layer of compact bone.
They are filled with spongy bone and red marrow.

9. Your Skeleton You have 206 bones in your skeleton.
Each bone is connected to other bones.
Wherever two bones connect or join, you have a joint.
Tough bands of tissue called ligaments hold the bones of a joint together.
Ligaments are strong, but they can bend to let your joints move.

10. Movable Joints Moveable joints let your skeleton bend in many places.
Hinge joints
Only fold open and shut, like a book.
Example—elbow, knee
Ball-and-socket joints
These joints let bones move in a circle.
Example—hips, shoulders

11. Movable Joints They have a slippery liquid between the bones.
This liquid acts like oil.
Joints have a tough stiff tissue called cartilage between the bones.

12. Immovable Joints Some bones fit too tightly too move.
These are immovable joints.
Example--skull

13. Skull A set of bones in the head. The brain fits inside the cranium.
Eyes fit in the eye sockets.
Jawbone is the only bone that moves in the skull.

14. Backbone The backbone holds up the top part of your body.
It is made of 25 vertebrae.
Pads of cartilage between the vertebrae cushion the bones and let your spine bend.
The spinal cord passes through holes in the vertebrae.

15. Ribs The bones of your chest are called rib cage.
There are 12 pairs of ribs attach to your spine.
10 of them attach to the breastbone in front.
The ribs make a cage around your heart and lungs.

16. Hipbones They support your body when you sit.
The hipbones are part of the pelvis.
The spine attached to the back of this large bone.
It contains and protects your bladder and some of your other organs.

17. Long Bones They help make big motions. Leg bones are thick and strong.
They hold up the entire weight of the body.

18. Hand Bones The small bones make up hand and fingers.
They give the ability to bend in many places.

19. Feet Bones The feet have many bones joined together.
These joints don’t bend much.
The foot makes a surface that you can balance on.
The arch in the middle of the foot makes the steps springy.