Infant Skull Fontanels: Anatomy, Functions & Closure

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The infant skull's bones are separated by fontanelles, or soft spots. At birth, the skull is incompletely developed, and fibrous membranes separate the cranial bones. These membranous areas are called fontanels. They permit some movement between the bones, so that the developing skull is partially compressible and can slightly change shape. This action enables an infant's skull to pass more easily through the birth canal.

The infant skull is different from an adult skull by the distinct separation of plates making up the skull. With this comes an element of malleability resulting in the infant skull's temporary image of the mother's pelvic opening. Equally noticeable is the soft spot at the top of the skull, which will remain until the plates grow together.

The anterior fontanelle and posterior fontanelle are the two areas of an infant's head where the skull bones have not completely covered the brain. The anterior fontanelle is located towards the front of the head. The posterior fontanelle is located at the upper back part of the head. The posterior fontanelle is no longer obvious when the infant is four months old. The anterior fontanelle can normally be felt until 9-16 months of age.

Eventually the fontanelles close as the cranial bones grow together. The posterior fontanelle usually closes about two months after birth; the sphenoid fontanelle closes at about three months, the mastoid fontanelle closes near the end of the first year, but the anterior one may not close until the middle or end of the second year.