The human skull is composed of many flat bones, and there will be gaps at the union of the bones. At the union of the two parietal bones, there is a gap, which is called the sagittal suture. Sagittal means arrow, because when shooting arrows, the arrow is mostly shot in the front and back position, so in the human anatomy, the front and back direction is called sagittal. The sagittal suture is described as the anterior-posterior direction bone suture in the middle of the top of the head. In normal adults, the sagittal suture is closed; in newborns, especially premature babies, the sagittal suture can be unclosed.