Calvaria

The calvaria (cranial dome) consists of mesoderm that ossifies straight away (intramembranous ossification in the desmocranium). The frontal and parietal bones and the squamous parts of the temporal bones (pars squamosa) as well as the interparietal part of the occipital bone (squama occipitalis) develop as flat bones with a protuberance (tuber). The squamous bones extend radially from their central protuberance. For a long time during growth, these bones allow for sufficient space for the increase in brain volume. Sutures (syndesmoses) form where the squamous bones meet. Gaps of connective tissue (fontanelles or fonticuli) remain free where more than two bones meet. The large quadrangular fontanelle (anterior fonticulus between frontal and parietal bones) only closes completely by the time the child is aged two years. The small triangular fontanelle (posterior fonticulus between parietal bones and occipital bone) ossifies during postnatal month 3.