The skull of an infant or young child is made up of bony plates that allow for growth of the skull. The borders at which these plates intersect are called sutures or suture lines. In an infant only a few minutes old, the pressure from delivery compresses the head, making the bony plates overlap at the sutures and creating a small ridge.
This is normal in newborns. In the next few days the head expands, the overlapping disappears, and the edges of the bony plates meet edge to edge. This is the normal position.
Ridging of the suture line can also occur when the bony plates fuse together too early. When this happens, growth along that suture line stops. Premature closure generally leads to an unusually shaped skull.
Premature closing of the suture running the length of the skull (sagittal suture) produces a long, narrow head. Premature closing of the suture that runs from side to side on the skull (coronal suture) leads to a short, wide head.