posted at http://en.wikipedia.org/wiki/Cranial_sutures
The crania (brain cases) of most vertebrates consist of sets of bony plates held together by cranial sutures. These sutures are held together mainly by Sharpey's fibers which grow from each bone into the adjoining one.
A suture is a type of fibrous joint which only occurs in the skull (or "cranium"). They are bound together by Sharpey's fibres. A tiny amount of movement is permitted at sutures, which contributes to the compliance and elasticity of the skull.
It is normal for many of the bones of the skull to remain unfused at birth. The fusion of the skull's bones at birth is known ascraniosynostosis. The term "fontanelle" is used to describe the resulting "soft spots". The relative positions of the bones continue to change during the life of the adult (though less rapidly), which can provide useful information in forensics and archaeology. In old age, cranial sutures may ossify (turn to bone) completely.[verification needed]
The joints between the teeth and the joint between the mandible and the cranium, the temporomandibular joint, form the only non-sutured joints in the skull.
The adult skull is normally made up of 22 bones. Except for the mandible, all of the bones of the skull are joined together by sutures, semi-rigid articulations formed by bony ossification, the presence of Sharpey's fibres permitting a little flexibility
Sutures - ridged
Ridged sutures refer to an overlap of the bony plates of the skull in an infant, with or without early closure.
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.