Areas on the head on which bone has not yet formed. The chief of these is the anterior fontanelle, situated on the top of the head between the frontal and two parietal bones. In shape it is four-sided, about 25 mm (1 inch) square at the time of birth, gradually diminishing until it is completely covered by bone, which should happen by the age of 18 months. The pulsations of the brain can be readily felt through it. Delay in its closure is particularly found in cases of RICKETS, as well as in other states of defective development. The fontanelle bulges in raised intracranial pressure from HYDROCEPHALUS and MENINGITIS, and depressed in DEHYDRATION.
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