Bone Structure

This image is the bone structure looked at from the inside and from the outside.
As you can see the parts are labeled, and you can follow with the paragraph.

       Bones have bumps, edges, round ends, rough spots and holes. The holes in the bones are helpful because they help the blood vessels and the nerves to enter into them.

Bone Tissue      Even though it's unbelievable, a bone is actually an organ! The living bone is made out of several different tissues and thus makes it an organ. The living bone's outer layer is covered with periosteum which is a tough and tightening membrane. The compact bone of the bone is the part of the bone which makes the bone stringer or harder. This strength is due to the deposits of calcium phosphate in the framework of the compact bone. In the center of the bone there are cavities which are filled by the spongy bone which contains marrow. There are two types of marrow cells, first, there are blood cells which are red and, second, there are fat cells which are yellow.

Cartilage
       Cartilages are tissues that cover the end of bones so that when two or more bones are near each other they won't rub against each other. Therefore this part of a bone must be slippery and smooth and this way it makes it easier for less friction to be produced. The cartilages are flexible and it helps the joints because it acts as s hock absorber and makes the job of the joints easier.