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Skull of a child. Coloured X-ray of the skull of a child, in side view. In the jaw can be seen the eruption of permanent teeth from the milk teeth. The face is at right. At top is the curved, rounded cranium of the skull which houses the brain. Cervical vertebrae of the neck are visible. Cavities of the nose are seen. The jaw houses numerous teeth (yellow) that can be seen positioned in different layers. These permanent (secondary) teeth are erupting to replace smaller milk (deciduous) teeth. Tooth replacement in children occurs between 6-12 years of age. (KEYSTONE/SCIENCE PHOTO LIBRARY/MEHAU KULYK/SCIENCE PHOTO LIBRARY)