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The skeleton of an adult human consists of 206 bones. It is composed of 270 bones at birth, which decreases to 206 bones by adulthood after some bones have fused together. Together, these bones form the axial skeleton and the appendicular skeleton. Many small and often variable bones, such as sesamoid bones and ossicles, are not included in this count.
The figure of 206 bones is commonly repeated, but dose have some peculiarities in its method of counting. It is taken of an adult human—the number of bones in the skeleton changes with age, as multiple bones fuse, a process which typically reaches completion in the third decade of life. In addition, the bones of the skull and face are counted as separate bones, despite being fused naturally. Some reliable sesamoid bones such as the pisiform are counted, while others, such as the hallux sesamoids, are not.
Individuals may have more or fewer bones than this owing to anatomical variations. The most common variations include additional (i.e. supernumerary) cervical ribs or lumbar vertebrae. Sesamoid bone counts also may vary among individuals.