Calvaria

The anterior part, or brow, is formed by the frontal bone, which extends backward to the coronal suture between the frontal bone and the parietal bones. The latter bones curve upward and inward to meet at the midline sagittal suture. Posteriorly, the parietal bones articulate with the triangular upper part of the occipital squama along the lambdoid suture. The meeting points of the sagittal suture with the coronal and lambdoid sutures are termed, respectively, bregma and lambda. In the fetal skull, they are the sites of the anterior and posterior fontanelles. The vertex, or highest point, of the skull lies near the middle of the sagittal suture. Parietal foramina are usually present; they transmit emissary veins passing between the superior sagittal sinus and the veins of the scalp.

The deeply concave internal, or endocranial, surface of the calvaria is made up of the inner aspects of the bones, sutures, and foramina mentioned above. The bones show indistinct impressions produced by related cerebral gyri, more evident grooves for dural venous sinuses and meningeal vessels, and small pits, or foveolae, for arachnoid granulations. Thus there is a median groove in the frontal, parietal, and occipital bones extending backward from the frontal crest to the internal occipital protuberance; it increases in width posteriorly and lodges the superior sagittal sinus. The frontal crest seen in the midline is produced by the coalescence of the anterior ends of the lips of the groove for the superior sagittal sinus. There are other, narrower grooves for meningeal vessels. The largest of these, the middle meningeal arteries and veins, leave their imprints in particular on the parietal bones, and the channels containing them may become tunnels where the anteroinferior angles of the parietal bones meet the greater wings of the sphenoid bone. The skull varies in thickness, and the area around the pterion is thin. It is relatively easily fractured by a blow to the side of the head, with possible tearing of the middle meningeal vessels. The resulting hemorrhage can be serious if it is not recognized and treated promptly.

The cut edge of the skullcap reveals that the constituent bones possess outer and inner laminae of compact bone separated by the diploë, a layer of cancellous bone. The outer lamina is thicker and tougher than the more brittle inner lamina.

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