Bones

Bones are formed by the ossification of cartilage.

All bones start off as cartilage in the womb, and gradually turn into bone.

They have a tough outer layer called the periosteum.

Some types of bone are light, but tough. These tend to contain red marrow, where red blood cells are made.

The marrow cavity contains yellow marrow, where white blood cells are made.

There are 4 different types of bone:

1. Long…like the femur

2. Short…like the carpels and tarsels

3. Flat…like some bones in the skull

4.  Irregular…like the vertebrae