A baby has more bones than an adult
A newborn skeleton has on the order of 300 bony elements. Many fuse, so a typical adult has 206.
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Several bones that are single in an adult begin as separate centres of ossification. The frontal bone is paired in the fetus. The hip bone is three bones — ilium, ischium, pubis — that fuse in adolescence. Vertebrae have pieces that join. The newborn total is usually given as about 270 to 300, depending on what is counted.
Fusion is why an adult wrist is a puzzle of eight carpals that used to be more cartilage than bone, and why some 'extra bones' on an X-ray of a child are ordinary growth, not fractures. The count falls as the person finishes building.
Caveats
- 300 is a rounded teaching number. Anatomists disagree at the margin about sesamoids and unfused centres.
- Fusion is not finished at birth's anniversary. Some plates close only in the late teens or twenties.
Sources
- 1Moore K. L., Persaud T. V. N., Torchia M. G.. The Developing Human. Elsevier, 10th edition, 2016.