Superior View (norma verticalis – fig. 313)

The outline of the skull, as seen from above, varies greatly in different specimens. In some the outline is more or less oval : in others it is more nearly circular, but its greatest width is usually nearer to the occipital than to the frontal region. This aspect of the skull is traversed by three sutures. (1) The coronal suture is placed between the serrated posterior edge of the frontal bone and the anterior borders of the parietal bones. From the median plane it passes downwards and forwards across the cranial vault. (2) The sagittal suture is placed in the median plane between the interlocking upper borders of the two parietal bones. (3) The lambdoid suture is placed between the posterior borders of the parietal bones and the superior border of the squamous part of the occipital bone. It runs downwards and forwards across the cranial vault. The meeting-place of the coronal and sagittal sutures is termed the bregma, and it is the site of a membrane-filled gap in the fetal skull which is named the anterior fontanelle. The lambda is situated at the junction of the sagittal and lambdoid sutures and is the site of the posterior fontanelle in the fetal skull, which is a similar but smaller gap.

Figure 313
Top of skull - Figure 313
The region of maximum convexity of the parietal bone is termed the parietal eminence (tuberosity) and can be identified easily in the living subject. In this situation the norma verticalis passes into the norma lateralis and the norma occipitalis, but there are no sharp lines of demarcation. The parietal foramen, which may be absent on one or both sides, pierces the parietal bone near the sagittal suture about 3.5 cm front of the lambda. It transmits a small emissary vein from the superior sagittal sinus within the skull, and this vessel constitutes one of the important connections between the extra- and the intracranial veins. Anteriorly the norma verticalis slopes down into the norma frontalis.

 


Previous | Next