Is the human skull made up of one bone or two?

Soft spots explained

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Is the human skull made up of one bone or two?

Asked by Jill Maynard of Greenacre, New South Wales, Australia

It surprises many to learn that the human skull is not one solid bone as is usually thought. Nor does it consist of just two bones---the top of the head and everything underneath. The skull (cranium) is actually composed of (count them!) twenty-two separate bones. There are eight cranial bones around the brain and fourteen facial and jaw bones in the human skull. Just one of these bones moves - the jaw bone (mandible). In infants and very small children, the cranial bones are disconnected segments held together by connective tissue stripes called sutures. At certain sites, these sutures are especially weak, creating the so-called “soft spots” (fontanels) in an infant’s head. The most prominent of these is a little way up from the infant’s forehead. When growing is complete, the bones of the skull fuse together along the suture lines. These unions contain small amounts of fibrous connective tissue similar to those of the joints of arms and legs. Although the skull may structurally appear to be one piece when fully developed, it is still composed of separate bones. Many fossil skeletal remains that anthropologists find often appear to have cracked or broken skulls. But these skulls are actually just missing some of their pieces. The softer connective tissue having decomposed, little support is left between the individual pieces in the skull. This causes them to fall out and perhaps get left behind over thousands and thousands of years. Has anyone seen my...? Then again, let’s not get a head of ourselves.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au

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