Ossify

hold. watch your wrist arrive.

hold to age a hand X-ray — the wrist fills in last

A newborn's wrist is mostly cartilage that ossifies bone by bone through childhood, so an X-ray shows a readable age, until the growth plates fuse in the late teens. A baby has more bones than an adult because they fuse.

Concepts: anatomy, growth.

An interactive you play with one thumb, on Wundr.