The persistence of the metopic suture is called metopism. This suture disappears by the second or third year of life. It is thought to be a normal variant of the cranial sutures . It forms from the lack of union of the two frontal bones during embryonic development.

Metopism is found in approximately 5% of Asians and 9% of European Caucasians and 1% of Blacks.

Reference:

Castillo SMA, Oda YJ, Santana GDM. “Metopism in Adult Skulls from Southern Brazil”. International Journal of Morphology. 2006; 24: 61-66.