All bones are made of compact and spongy bone tissues. The compact tissue makes the outer part of the bone. The spongy tissue occupies the inner part. However, bones show great variation in their shapes and sizes.

They can be classified on the basis

- of their shape

- and of the presence or not of a large cavity devoided of bone tissue right in the center of the bone.

Bones are classified as

- long bones,

- short bones,

- flat bones,

- irregular bones.