Definition of Fontanel (fontanelle)

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Fontanel (fontanelle): The word fontanel comes from the French fontaine for fountain. The medical term fontanel is a "soft spot" of the skull. The "soft spot" is soft precisely because the cartilage there has not yet hardened into bone between the skull bones. There are normally two fontanels, both in the midline of the skull, one (the anterior fontanel) well in front of the other (the posterior fontanel). The posterior fontanel closes first, at latest by the age of 8 weeks in a full-term baby. The anterior fontanel closes at 18 months of age on the average but it can close normally as early as 9 months. If fontanels close too early or too late, that may be a sign of a problem.