The skull bone that moves
Most of your skull bones are locked together. Your lower jaw is different. It's the only skull bone you can move on purpose.
It is shaped like a horseshoe, or a big letter U. The front makes your chin. The two back ends reach up toward your ears.
It is the biggest and strongest bone in your face. It needs to be, because chewing pushes on it all day long.
Feel your jaw joint
Your jaw hooks onto your skull at two joints, one just in front of each ear. These joints are some of the busiest in your body. They work every time you talk, chew, yawn or laugh.
Try it: put your fingertips just in front of your ears. Now open and close your mouth slowly. Feel that bump moving? That's your jaw joint.
Your jaw can do more than open and shut. It can slide forward, back and side to side. Try moving your chin side to side, like a cow chewing grass.
A home for teeth
Your bottom teeth grow out of your jaw bone. Each tooth sits in its own little pocket in the bone.
Kids have 10 baby teeth on the bottom. Under them, grown-up teeth are already waiting inside the jaw bone. When a baby tooth wiggles out, a grown-up tooth moves up to take its place.
Your jaw grows longer as you grow up. That makes room for more grown-up teeth at the back.
Two halves that join
A baby's jaw bone starts out as two halves, a left one and a right one. They meet in the middle of the chin.
During the first year of life, the two halves join into one strong bone.
Try it: run a finger along the bottom of your chin. You can't feel a seam now, because the two halves grew together long ago.