ANOMALOUS PARIETAL SUTURES AND THE BIPARTITE PARIETAL BONE

1. The literature on anomalous parietal sutures and embryogenesis of the parietal bone is reviewed.

2. New embryogenic studies are presented which indicate that the normal parietal bone usually ossifies from a single center which appears during 8-12 weeks of gestation. For reasons not presently understood, the parietal bone sometimes (rarely) ossifies from 2 separate centers which fail to unite. These centers remain separated by an anomalous suture.

3. The anomalous parietal bone is usually larger than the normal side with the increased bone growth occurring perpendicular to the suture line.

4. The phylogenetic background of parietal sutures is discussed. Noteworthy is the increased incidence of such sutures in subhuman primates and the tendency of these sutures to be vertically oriented in these animals compared with the horizontal orientation in man.

5. The differential diagnosis of the anomalous suture from fractures and membranous unossified strips is discussed.

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