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At birth the skull is large in proportion to the other parts of the skeleton, but its facial portion is small, and equals only about one-eighth of the bulk of the cranium as compared with one-half in the adult. The frontal and parietal eminences are prominent. Ossification of the skull bones is not completed, and many of them, for example, the occipital, temporals, sphenoid, frontal, and mandible, consist of more than one piece. Unossified regions between neighboring bones, termed fontanelles, are seen at the angles of the parietal bones; these fontanelles are six in number: two, an anterior and a posterior, are situated in the middle line, and two, an anterolateral and a posterolateral, on either side. The anterior fontanelle is the largest, and is placed at the junction of the sagittal, coronal, and frontal sutures. The posterior fontanelle is triangular in form and is situated at the junction of the sagittal and lambdoidal sutures. The lateral fontanelles are small, irregular in shape, and correspond respectively with the sphenoidal and mastoid angles of the parietal bones. The smallness of the face at birth is mainly accounted for by the rudimentary condition of the maxillae and mandible, the non-eruption of the teeth, and the small size of the maxillary air sinuses and nasal cavities. The skull grows rapidly from birth to the seventh year, by which time the foramen magnum and petrous parts of the temporal bones have reached their full size and the orbital cavities are only a little smaller than those of the adult. Growth is slow from the seventh year until the approach of puberty, when a second period of activity occurs. This second period of growth activity results in an increase in all directions, but it is especially marked in the frontal and facial regions, where it is associated with the development of the air sinuses.