Babies' skeletons have 300 parts, adults' have 206

Human skeleton

Fusing bones: Babies' skeletons have 300 parts, adults' have 206

Long bone growth: Stops around the end of puberty

Babies have more cartilage than bone

The skeleton of a newborn baby is made up of more than 300 parts, most of which are made of cartilage. Over time, most of this cartilage turns into bone, in a process called ossification. As the baby grows, some of its bones fuse together to form bigger bones. By adulthood, your skeleton contains just 206 bones.

How bones grow in length

A long bone, such as your femur (thigh bone), grows in length at either end in regions called growth plates. Growth occurs when cartilage cells divide and increase in number in these growth plates. These new cartilage cells push older, larger cartilage cells towards the middle of a bone. Eventually, these older cartilage cells die and the space they occupied is replaced with bone. When a bone has reached its full size, its growth plates are converted into bone.

Long bone growth comes to an end around the end of puberty. When long bone growth stops, you stop getting taller.