The normal skull on the left shows the direction of growth at the cranial sutures. The size of the arrows depicts a rate of growth - larger means more growth. The skull on the right show  sagittal suture craniosynostosis  where the long suture running back to front on the top of the skull is closed. This closed suture limits widening of the skull. The remaining open sutures must produce more bone to keep up with the growing brain, but they can only grow in one direction. In this case this  compensatory growth  causes the skull to have an abnormally long and narrow shape (scaphocephaly)