As you grow your bones change per portion and amount. In your life you will lose about six hundred bones. When in the womb a child has over eight hundred bones. At birth four hundred fifty. An adult has two hundred six bones.
Fusion makes it possible.
This cartilage hardened and became bone. There are disks of cartilage between the vertebrae in your back. This allows you to bend and twist. The disk cartilage shrinks but permanent cartilage does not that is how your nose and ears grow.