SkeletonClear

How does the skeletal system work?
Your skeleton is 206 living bones: a frame, a shield, a set of levers and a blood factory. Count every bone, cut a femur open, bend five kinds of joint, feel how hard your biceps pulls, watch a growth plate close and a broken bone knit.

▶ Play with it  ·  Read the 60-second explainer  ·  Watch the 40-second video

1. 206 bones, head to toe. A typical adult has 206 bones: 80 down the middle (skull, ear bones, hyoid, spine and ribs) and 126 in the girdles and limbs. More than half are in the hands and feet. A newborn has about 270 to 300 pieces that fuse as it grows.
2. Inside a bone. A femur is a living tube: periosteum outside, compact bone built from osteons, spongy bone at the ends with red marrow making about 2 million red cells a second, and yellow marrow in the hollow shaft. A tube is stiffer and stronger than a solid rod of the same weight.
3. Where bones meet. Hinges (knee, elbow), balls in sockets (hip, shoulder), a pivot at the top of the neck, gliding wrist bones and fixed skull sutures. Cartilage and synovial fluid make joints more slippery than ice on ice. Ligaments join bone to bone; tendons join muscle to bone.
4. Levers and load. The forearm is a class 3 lever: the biceps pulls 7 to 8 times the load to buy speed. The ground pushes about 1.2 times body weight when you walk and 2.5 times when you run; the hip carries up to about 5 times. Bend at the knees and keep school bags under about 10% of body weight.
5. Bone is alive. Osteoclasts dig out old bone and osteoblasts fill the gap, renewing about 10% of the skeleton a year. Bones hold 99% of the body's calcium, banked with the help of vitamin D from sunlight. Growth plates make children taller, then close in the late teens.
6. Keeping bones healthy. Fractures heal with new bone in about 6 to 12 weeks. Bone mass peaks around 30; osteoporosis thins it later, especially in women after menopause. Osteoarthritis wears cartilage; scoliosis curves the spine; sprains tear ligaments. Exercise, calcium and vitamin D help. For your own health, see a doctor.

From bark splints in Egypt to 3D-printed bones: 4,500 years of learning how bones hold us up, grow and heal.

• 600 BCE · Bamboo splints and bone-setting in India (Sushruta (attributed), Kashi (Varanasi), India)
• 1543 · The fabric of the human body (Andreas Vesalius, Padua, Italy (printed in Basel, Switzerland))
• 1691 · Tiny canals inside bone (Clopton Havers, London, England)
• 1851 · The plaster cast (Antonius Mathijsen, Haarlem, Netherlands)
• 1895 · Anna Bertha's hand (Wilhelm Röntgen and Anna Bertha Röntgen, Würzburg, Germany)
• 1951 · Rings that grow new bone (Gavriil Ilizarov, Kurgan, Siberia)
• 1962 · The low-friction hip (John Charnley, Wrightington Hospital, Lancashire, England)
• 1968 · The Jaipur Foot (Ram Chandra Sharma and Dr P. K. Sethi, Jaipur, Rajasthan, India)

The full story, with 30 moments, charts, people and 41 sources: glassbox.how/e/skeletonclear/history. The data lives in history.json.

Made with the Glassbox studio from this box's storyboard (window.glassbox.director). Free to reuse under CC BY 4.0.

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• Code: MIT. Use it, change it, ship it.
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• Third-party parts keep their own licences: three.js (MIT), Geist, Instrument Serif (SIL OFL 1.1).
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Found a mistake? Open an issue. Corrections happen in public.

It's plain HTML, CSS and JavaScript. No build step and no dependencies. Run locally, it contacts no other website.

python3 -m http.server 8000

Three.js and the fonts ship in vendor/ and fonts/, so it also works offline.

Then open http://localhost:8000.