Human Skeleton

The skeleton is not unchanging; it changes composition over a lifespan. Early in gestation, a fetus has no hard skeleton — bones form gradually during nine months in the womb. At birth, all bones will have formed, but a newborn baby has more bones than an adult. On average, an adult human has 206 bones in their skeleton (the number can vary slightly from individual to individual), but a baby is born with approximately 270. The difference comes from a number of small bones that fuse together during growth. These include the bones in the skull and the spine. The sacrum (the bone at the base of the spine) consists of six bones which are separated at birth but fuse together into a solid structure in later years.

Not all bones are interconnected directly. There are 6 bones (three on each side) in the middle ear that articulate only with themselves. Another bone, the hyoid bone in the neck, does not touch any other bones in the body but is rather supported by muscles.

The longest bone in the body is the femur and the smallest is the stapes bone in the middle ear.