Human Skeleton: 206 Bones, Skull, Spine and Ribs in 3D

Two halves of one frame

The picture shows all 206 bones at once. Anatomists split them into two groups. The axial skeleton is the central axis: the skull, the spine, the ribs and the breastbone, 80 bones in all. The appendicular skeleton is everything that hangs from that axis, the arms, legs, shoulders and hips, 126 bones. Here is a surprise: more than half of all your bones are in your hands and feet. Each hand has 27 bones and each foot has 26, which makes 106. Pick any region in the sandbox and it lifts out of the skeleton with its name and its count.

The skull and its one moving part

The model zooms in on the head. The skull is made of 22 bones: 8 cranial bones that form a helmet around the brain and 14 facial bones that shape the face. They are locked together by jagged seams called sutures, and only one of them moves freely, the lower jaw, or mandible. That is why you can chew and talk. Tiny ear bones also move, but they sit inside the ear and are counted separately. The smallest bone in the whole body, the stapes, is one of them and is only about 3 millimetres long.

Counting the vertebrae

Now the camera slides down the back. The spine has 33 vertebrae in five regions. At the top are 7 cervical vertebrae in the neck. Below them come 12 thoracic vertebrae, each joined to a pair of ribs, and then 5 lumbar vertebrae in the lower back, the largest and strongest. At the bottom are 5 sacral vertebrae, fused into one bone called the sacrum, and 4 small coccygeal ones, fused into the tailbone. Soft discs between the separate vertebrae act as cushions. Seen from the side, a healthy spine has a gentle S shape that works like a spring.

Twelve pairs of ribs

Next the picture opens the chest. There are 12 pairs of ribs, 24 in all, and all of them attach at the back to the thoracic vertebrae. The top seven pairs connect to the breastbone, or sternum, through bars of cartilage, the next three connect to the cartilage above them, and the last two pairs, the floating ribs, have free ends. The rib cage shields the heart and the lungs, yet it is springy enough to widen when you breathe in. The ribs hang on the spine by small movable joints, and the model now lights up the hinges of the whole body.

Joints, the hinges of the body

A joint is where two bones meet. Some joints, like the seams of the skull, hardly move at all. Others are built for motion. The hip and shoulder are ball-and-socket joints that swing in nearly every direction. The elbow and knee work mostly like hinges, bending in one plane. In the neck, the top vertebra turns on the one below it, a pivot that lets you shake your head. Ends of bones are coated in smooth cartilage, and tough straps called ligaments hold the bones together. The thigh bone, the femur, is the longest and strongest, about a quarter of a person's height.

Cut a bone open

The last moment slices a long bone in half. Under a thin outer skin lies compact bone, dense and smooth, which carries most of the load. Inside, near the ends, is spongy bone, a lattice of tiny struts that keeps the bone light but strong, much like the steel frame of a bridge. And in the hollow centre and in the spongy parts sits bone marrow. Red marrow is a factory that makes red blood cells, white blood cells and platelets, millions of new red cells every second. Bone is alive: it is rebuilt all the time, and exercise makes it stronger.

The skeleton: 206 bones