The human skeleton is made of bones, some of them joined together, supported and supplemented by a structure of ligaments,
tendons, muscles, and cartilage.
The skeleton changes composition over a lifespan. Early in gestation, a fetus has no hard skeleton - bones form gradually
during nine months in the womb. When a baby is born it has more bones than it will as 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.