The Human Skeleton: Bones and Joints

A healthy adult has exactly 206 bones. Babies start life with around 270 bones, and many gradually fuse together during childhood and early adulthood until only 206 remain.

The femur, or thigh bone, is the longest and strongest bone in the body. It runs from the hip down to the knee and can support up to 30 times a person's body weight.

The stapes (stirrup bone) in the middle ear is the smallest bone in the body, measuring only about 3 millimeters long — roughly the size of a grain of rice.

Tooth enamel, the outer coating of your teeth, is the hardest substance the human body produces — even harder than bone. It rates 5 on the Mohs hardness scale, close to steel.

Newborn babies have roughly 270 bones, many of which are soft cartilage. As children grow, these bones harden and fuse, leaving adults with just 206.

The cervical spine has exactly 7 vertebrae (labeled C1 through C7). Interestingly, giraffes also have exactly 7 cervical vertebrae — theirs are just much, much longer.

The human rib cage contains 12 pairs of ribs — 24 ribs in all — forming a protective cage around the heart and lungs. The first 7 pairs attach directly to the breastbone.

The 11th and 12th rib pairs are called floating ribs because they connect only to the spine in the back and have no attachment — direct or indirect — to the sternum at the front.

The patella is the small, flat, rounded bone that sits at the front of the knee joint. It protects the joint and acts as a lever to help the muscles straighten the leg.

The clavicle, or collarbone, is the slender S-shaped bone connecting the shoulder blade to the breastbone. Because people instinctively use their arms to break a fall, it breaks very easily.

The calcaneus is the large bone at the back of the foot that forms the heel. It bears the brunt of our body weight every time we take a step and is the largest of the 26 bones in the foot.

The radius (on the thumb side) and the ulna (on the little-finger side) are the two bones of the forearm. The radius rotates over the ulna to allow your wrist to turn palm-up or palm-down.

Red blood cells are produced in the red bone marrow, found mainly in flat bones like the sternum, ribs, and pelvis in adults. The body produces about two million new red blood cells every second.

The stapes (stirrup) transmits sound vibrations from the incus bone onward to the oval window of the inner ear, where they are converted into nerve signals the brain interprets as sound.

The sphenoid bone sits at the base of the skull and has wing-like extensions that spread outward on both sides, giving it a distinctive butterfly or bat shape that anatomy students remember well.