The paired sphenoid fonticuli close by the time the child is aged 1 year. They are delimited by the frontal, parietal, temporal and sphenoid bones. The mastoid fonticuli close by the time the child is aged 18 months. These are bordered by the parietal, occipital and temporal bones. The mastoid processes develop only after birth, which is why the facial nerve may be damaged by manipulations during childbirth. Flexibility of the cranial bones facilitates the passage of the child's head through the birth canal.