The part of the bone above the highest nuchal line is known to ossify in membrane and may not fuse with the rest of the part even in adulthood, creating the interparietal bone.
In one case, completely separate interparietal bone is found which sutures the rest of the occipital bone at highest nuchal line (Figure 7).
In Figure 7, it can be clearly seen that complete interparietal bone is formed by fusion of all the nuclei and the suture between it and rest of the occipital bone lies at the level of highest nuchal line. [5, 6] This indicates that the bone developing from middle and upper pairs of nuclei was part of parietal bone in early mammalian phylogeny and it has now come to join the occipital bone in primates and man. Further, the intermediate segment which lies between the superior and highest nuchal lines remains fused with supraoccipital part of occipital bone.