Human bones are formed from growth plates which consist of columns of multiplying cartilage cells that grow in length. The cells then change into hard, mineralized bone and into a mature skeleton. Bone building is a life process that is facilitated by bone cells namely; osteoblasts, osteocytes and osteoclasts.
How Many Bones in a Human? – http://answers.ask.com/Health/Other/how_many_bones_in_a_human