Origin of the calvaria and its sutures.

Studies indicate that the dura is the guiding tissue in the morphogenesis of the calvaria and its major sutures, which develop from ten to 16 weeks of fetal life. Overlying the central zones between the dural reflections ossification takes place, whereas none occurs over the reflections of dura, these being the suture sites. Strong evidence for the role of the dural reflections in determining the suture sites was obtained from the evaluation of instances of major brain malformations that must have antedated calvarial morphogenesis. These included holoprosencephaly, craniopagus, and dicephaly. The altered dural reflections, which related to the aberrant form of the brain, coincided with the position of the unusual sutures. Furthermore, a lack of a dural reflection was accompanied by a lack of development of a suture at that site.