The Skeleton

All 17 parts, one by one

• 1 Skull The bony helmet around your brain, made of curved plates joined by wiggly seams. Head & neck

  What it does

  Wraps your brain in hard bone, holds your eyes in deep sockets, and gives your face its shape. The wiggly seams, called sutures, lock together like jigsaw pieces — a curved dome spreads a knock outwards instead of letting it punch straight through.

  Find it on you

  Run your fingers over the top of your head and press gently. That solid curve under your hair is the top of your cranium. Now feel the hard ridge just above your eyebrows — the roof of your eye sockets.

  Looking after it

  Wear a helmet for cycling, scootering and skating. Your skull is strong, but your brain is soft and floats in fluid, so a hard bang can shake it even when the bone is fine.

  Amazing facts

  • The skull is 22 bones, not one: 8 wrapped around the brain and 14 making your face.
  • A baby is born with soft gaps between the skull plates called fontanelles. The big one on top closes at around 18 months.
  • The smallest bone in your whole body, the stapes, is tucked inside your ear and is about the size of a grain of rice.
  22 bones

  Cranium

  The part of the skull that surrounds the brain.

  Suture

  A wiggly, locked-together joint between two skull bones.

• 2 Jawbone The horseshoe-shaped bone that holds your bottom teeth and swings up and down. Head & neck

  What it does

  Works as a nutcracker. Two hinges just in front of your ears let it open, close and slide sideways, so your teeth can crush and grind food into pieces small enough to swallow.

  Find it on you

  Put a finger just in front of each ear and open your mouth wide. You can feel the hinge move — that is your jaw joint working.

  Looking after it

  Chewing on hard things like ice or pen lids can chip teeth and ache the joint. Grinding your teeth when you are stressed makes it sore too.

  Amazing facts

  • It is the only bone in your skull that moves freely. Every other one is locked in place.
  • It is also the strongest and hardest bone in your face.
  • Your back teeth can bite down with roughly the force of a grown-up standing on them.

  Mandible

  The proper name for the lower jawbone.

  Temporomandibular joint

  The jaw hinge in front of your ear. Doctors shorten it to TMJ.

• 3 Spine A stack of small ring-shaped bones running from the base of your skull to your bottom. Head & neck

  What it does

  Does two opposite jobs beautifully. It holds your whole upper body up, and it bends. Each bone only tilts a tiny bit, but 24 tiny tilts added together let you curl into a ball. Down the hollow middle runs your spinal cord, the thick bundle of nerves carrying messages between your brain and the rest of you.

  Find it on you

  Reach behind your neck and feel the row of bumps down the middle of your back. Bend forward and the bumps stick out more — those are the tips of your vertebrae.

  Looking after it

  Carry a school bag on both shoulders rather than one, and get up and move about often. Backs get stiff and achy from sitting still, not from being used.

  Amazing facts

  • There are 33 bones in a baby spine. In an adult, 9 of them have fused into the sacrum and tailbone, leaving 26 separate pieces.
  • Between the bones are springy cushions called discs, which squash down slightly during the day. You really are about a centimetre taller when you wake up.
  • Almost every mammal has exactly 7 neck bones — you, a mouse, and a giraffe.
  26 pieces

  Vertebra

  One single bone of the spine. Many of them are vertebrae.

  Spinal cord

  The nerve bundle inside the spine, carrying messages.

• 4 Collarbone A slim, gently S-shaped bone lying across the top of your chest. Chest & shoulders

  What it does

  Acts as a strut. It props your shoulder out sideways, away from your ribcage, which is what gives your arm room to swing in a huge circle. Without it your shoulders would collapse inwards towards your chest.

  Find it on you

  Run a finger from the notch at the base of your throat straight outwards. That hard ridge just under the skin, all the way to the point of your shoulder, is your collarbone.

  Looking after it

  It sits right under the skin with nothing to pad it, which is why falling onto an outstretched arm can snap it. It is the bone children break most often.

  Amazing facts

  • It is the only long bone in your body that lies horizontally.
  • It is the first bone to start hardening, about five weeks after a baby starts growing, and the last to finish, at around 25 years old.

  Clavicle

  The proper name for the collarbone.

• 5 Shoulder blade A flat triangle of bone gliding across the back of your ribcage. Chest & shoulders

  What it does

  Gives your shoulder its enormous range. It holds the shallow cup your arm bone sits in, and rather than being bolted to your spine it slides around on a raft of muscles, so when you reach overhead the blade swings round to follow.

  Find it on you

  Reach one hand over the opposite shoulder onto your back. Feel the flat plate and the hard ridge running across it, then move your arm — the whole thing travels.

  Looking after it

  Slumping forward all day lets the blades drift apart and the muscles holding them get weak. Hanging, climbing and swimming keep them strong.

  Amazing facts

  • It is barely attached to the rest of the skeleton — the only bony link is through the collarbone.
  • Around 17 different muscles pull on each shoulder blade.
  • It is also called the wing bone, because in birds this is where the wing anchors.

  Scapula

  The proper name for the shoulder blade.

• 6 Breastbone A flat dagger-shaped bone down the middle of your chest. Chest & shoulders

  What it does

  Is the front anchor of your ribcage. Ribs curve round from your spine and clip onto it through bendy cartilage, closing the cage into a strong hoop while still letting it flex every time you breathe in.

  Find it on you

  Press the flat bone in the centre of your chest, between where the ribs meet. Slide down to the bottom tip — that small pointed end is the xiphoid process.

  Looking after it

  It shields your heart and the big blood vessels above it, so it takes the hit in a seatbelt or a tackle. That bruising ache after a hard fall is usually the cartilage, not the bone.

  Amazing facts

  • It starts life as three separate pieces that slowly fuse into one.
  • Because it sits directly over the heart, it is the spot rescuers push on when giving CPR.

  Sternum

  The proper name for the breastbone.

• 7 Ribs Twelve pairs of curved bones sweeping from your spine round to the front of your chest. Chest & shoulders

  What it does

  Builds a springy cage around your heart and lungs. It is not a rigid box: muscles between the ribs lift the whole cage up and out when you breathe in, making more room inside so air rushes down into your lungs.

  Find it on you

  Put your hands on the sides of your chest and take a slow deep breath. Feel the cage swing outwards and upwards, then sink back down.

  Looking after it

  Ribs bend before they break, which is lucky. Deep, slow breathing keeps the muscles between them working well, and is one of the quickest ways to calm a racing body down.

  Amazing facts

  • The top 7 pairs join the breastbone directly. The next 3 pairs join the cartilage above them, and the bottom 2 pairs, called floating ribs, do not reach the front at all.
  • The cage moves roughly 20,000 times a day, because that is how often you breathe.
  • Nearly everyone has 12 pairs, but about 1 person in 200 grows an extra small rib up in the neck.
  12 pairs
• 8 Upper arm bone The single long bone between your shoulder and your elbow. Arms & hands

  What it does

  Turns your arm into a crane. The rounded top sits in the shallow socket of your shoulder blade — the loosest joint in the body — which is why you can swing your arm in a full circle. The bottom end makes the hinge of your elbow.

  Find it on you

  Grip your upper arm and wiggle it. The one solid rod you can feel through the muscle is the humerus. Now find the bony knob on the inside of your elbow.

  Looking after it

  Because the shoulder joint is so shallow and mobile, it is also the easiest one to pull out of place. Warm up before throwing hard or hanging off things.

  Amazing facts

  • The tingly "funny bone" is not bone at all. It is the ulnar nerve, running in a groove behind that knob at your elbow with nothing to protect it.
  • The shoulder is the most movable joint you own, and it pays for that freedom by being the one that dislocates most.

  Humerus

  The proper name for the upper arm bone.

• 9 Forearm bones Two bones side by side between elbow and wrist: the radius on the thumb side, the ulna on the little-finger side. Arms & hands

  What it does

  Lets you twist. The ulna stays put as the hinge of your elbow while the radius rolls right over the top of it, carrying your hand from palm-up to palm-down. That single trick is why you can turn a doorknob, use a screwdriver, or hold a bowl steady.

  Find it on you

  Rest your forearm on a table palm up, then turn it palm down while watching the skin. Feel with your other hand and you can sense one bone crossing over the other.

  Looking after it

  Falling onto an outstretched hand pushes all your weight up through the radius, so the wrist end of it is the bone adults break most. Landing rolled up beats landing stiff-armed.

  Amazing facts

  • Radius means "spoke of a wheel" in Latin, because it sweeps round like one.
  • Ulna comes from the old word for elbow — the pointy bit of your elbow is the top of it.

  Radius

  The forearm bone on the thumb side, which rotates.

  Ulna

  The forearm bone on the little-finger side, which makes the elbow.

• 10 Wrist & hand bones A crowd of small bones: 8 pebbles in the wrist, 5 long bones through the palm, and 14 in the fingers and thumb. Arms & hands

  What it does

  Trades strength for cleverness. Lots of small bones means lots of joints, and lots of joints means your hand can flatten, cup, pinch, grip a bar or thread a bead. Your thumb swings across to meet every fingertip, which is what makes a human hand so useful.

  Find it on you

  Spread your fingers and look at the back of your hand. The long ridges are the bones of your palm. Now touch your thumb to each fingertip in turn.

  Looking after it

  Small joints get sore from doing the same movement for hours. Shake your hands out and stretch your fingers when you have been writing or gaming for a long while.

  Amazing facts

  • Each hand has 27 bones. Both hands together hold more than a quarter of all the bones in your body.
  • There are no muscles inside your fingers. They are pulled by long tendons like puppet strings, with the muscles up in your forearm — which is why your forearm bulges when you make a fist.
  • Your thumb has 2 finger bones. Every other finger has 3.
  27 bones each
• 11 Pelvis A wide bowl of bone at the base of your spine, with a deep socket on each side for your leg. Hips & legs

  What it does

  Is the crossroads of your whole body. Everything above it presses down through your spine into the bowl, and the bowl passes that weight out to your two legs. It also cradles your bladder and the lower end of your intestines, and gives your biggest muscles something to pull against.

  Find it on you

  Put your hands on your hips and press down until you hit bone. Those hard ridges are the top rims of the bowl.

  Looking after it

  Sitting down for hours lets the hip muscles shorten and tighten. Walking, running and climbing stairs keep the whole area strong and comfortable.

  Amazing facts

  • Each side starts as three separate bones — ilium, ischium and pubis. They fuse into one solid hip bone in your teens.
  • The hip socket is deep and cupped, the opposite of the shallow shoulder. That is a swap of freedom for stability, because your hip has to hold your whole weight.

  Ilium

  The broad flaring blade of the hip bone you rest your hands on.

• 12 Thigh bone The long bone from hip to knee, and the biggest bone you have. Hips & legs

  What it does

  Carries you. It takes your body weight down to the knee, and its ball-shaped top spins in the hip socket so you can walk, run, kick and climb. It is slightly angled inwards, which brings your knees under your centre and stops you walking like a penguin.

  Find it on you

  Sit down and press into the front of your thigh through the muscle. The solid bar you reach is the femur. Feel the bony knob at the outside of your hip — that is the top of it.

  Looking after it

  Bone grows stronger when you land on it, so running, jumping and skipping build a thicker, tougher femur. Sitting still all day does the opposite.

  Amazing facts

  • It is the longest, heaviest and strongest bone in your body, usually about a quarter of your height.
  • When you run, it carries several times your body weight with every stride.
  • Its round head and deep socket make a ball-and-socket joint — the same design as a joystick.
  About ¼ of your height

  Femur

  The proper name for the thigh bone.

• 13 Kneecap A small shield of bone floating in the tendon at the front of your knee. Hips & legs

  What it does

  Works as a pulley. Your big thigh muscle pulls on your shin through a tendon, and the kneecap holds that tendon further forward from the joint, giving the muscle better leverage. Straightening your knee is around a third harder without it. It also shields the joint when you land on your knees.

  Find it on you

  Sit with your leg straight and relaxed and wobble your kneecap side to side with your fingers. Now tighten your thigh — it locks in place and stops moving.

  Looking after it

  Kneecap pain is common in growing legs, especially when running or jumping increases quickly. Strong thigh and hip muscles keep it tracking in its groove.

  Amazing facts

  • It is the largest sesamoid bone — a bone that grows inside a tendon rather than joining onto other bones.
  • Babies are born with a kneecap made of soft cartilage. It only hardens into bone at around 3 to 5 years old.

  Patella

  The proper name for the kneecap.

• 14 Shin & calf bones Two bones between knee and ankle: the thick tibia at the front, the slim fibula on the outside. Hips & legs

  What it does

  Splits the work. The tibia is the pillar, taking almost all of your weight down to the ankle. The fibula barely carries any load — it is there as an anchor for muscles and to build the outer wall of your ankle, which stops your foot rolling off sideways.

  Find it on you

  Run a finger down the front of your shin. That sharp edge with no muscle over it is the tibia. Now feel the bony bump on the outside of your ankle — that is the bottom of the fibula.

  Looking after it

  Aching shins usually mean too much running on hard ground too quickly. Build up slowly and wear shoes that cushion your landing.

  Amazing facts

  • The tibia is the second longest bone in your body, after the thigh bone.
  • The fibula carries less than a tenth of your weight. Surgeons can borrow a piece of it to rebuild bone elsewhere in the body.

  Tibia

  The shin bone, the thick weight-carrying one.

  Fibula

  The slim outer bone that forms the outside of your ankle.

• 15 Ankle & foot bones Twenty-six bones per foot: 7 chunky ones in the heel and ankle, 5 long ones through the middle, and 14 in the toes. Hips & legs

  What it does

  Is a spring and a lever in one. The bones are stacked into arches held by tough bands, so when you land the arch flattens slightly and soaks up the shock, then springs back to push you into the next step. Your toes grip and balance you at the end of each stride.

  Find it on you

  Stand up barefoot and look at the inside of your foot. The curve lifting away from the floor is your arch. Rise onto your toes and feel it lift higher.

  Looking after it

  Going barefoot at home and walking on grass and sand make the small muscles that hold your arches up work harder, which keeps them strong.

  Amazing facts

  • Your two feet contain 52 bones — about a quarter of your entire skeleton.
  • The heel bone, the calcaneus, is the largest bone in your foot and the first to hit the ground when you walk.
  • A typical person walks far enough in a lifetime to go around the world about four times.
  26 bones each
• 16 Joints & cartilage The living gap where two bones meet, capped with slippery cartilage and sealed in a bag of fluid. Inside a bone

  What it does

  Stops bone grinding on bone. Each bone end is capped with smooth cartilage and the sealed capsule is filled with a slippery liquid, so the surfaces glide with less friction than ice on ice. Tough straps called ligaments tie the bones together so the joint bends only the way it should.

  Find it on you

  Bend and straighten your elbow slowly. It only hinges one way. Now circle your shoulder — a ball and socket goes everywhere. Different shapes, different jobs.

  Looking after it

  Movement is what feeds a joint: cartilage has no blood supply of its own and gets its nutrients squeezed in and out of the fluid as you move. Joints stiffen from being still.

  Amazing facts

  • Cartilage is one of the most slippery materials known — far more slippery than a wet ice rink.
  • The knee is the largest and most complicated joint in the body.
  • That pop when you crack a knuckle is a bubble forming in the joint fluid. It does not cause arthritis.

  Ligament

  A tough band tying bone to bone.

  Tendon

  A tough cord tying muscle to bone.

  Cartilage

  Smooth, rubbery tissue capping the ends of bones.

• 17 Inside a bone A hard outer shell, a honeycomb of struts inside it, and soft marrow filling the middle. Inside a bone

  What it does

  Gets maximum strength for minimum weight, and runs a factory at the same time. The outer shell is dense, but inside, the bone is a honeycomb with the struts lined up along the lines of force — like the girders of a bridge. In the hollow spaces, red marrow makes new blood cells.

  Find it on you

  You cannot feel this one from outside, which is what the cutaway on the thigh bone is showing. If you have ever seen a bone in a piece of meat, the spongy middle is exactly this.

  Looking after it

  Calcium from food such as milk, cheese, beans and leafy greens is the raw material. Vitamin D, which your skin makes in sunlight, is what lets your body actually absorb it.

  Amazing facts

  • Your marrow makes around 2 million new red blood cells every second.
  • Bone is constantly torn down and rebuilt. You get a more or less new skeleton every 10 years.
  • For its weight, bone is stronger than steel and much lighter, because of that honeycomb inside.
  2 million cells a second

  Marrow

  The soft tissue in the middle of a bone, where blood is made.

  Spongy bone

  The light honeycomb of struts inside the hard outer shell.