The Parietal Bone
The parietal bones are found on both sides of the neurocranium, forming large parts of the top and the side of the head. The bones are roughly square shaped and lie under the vertex. It has a concave internal surface and a convex external surface. The internal surface is covered with grooves for the middle meningeal artery that occur due to the arterial pressure causing the bone to recede. Other markings are the groove for sigmoid sinus near the mastoid angle and the groove for superior sagittal sinus.
The external surface features the superior and inferior temporal lines where the temporal fascia and temporal muscle attach to, respectively. A parietal emissary vein connects the superior sagittal sinus with the veins of the scalp through the parietal foramen which is located at the back of the parietal bones.
The two parietal bones meet each other in the midline of the skull roof forming a serrated margin known as the sagittal suture. Apart from its opposite counterpart, each parietal bone is surrounded by four other bones:
- anteriorly it borders with the frontal bone (→coronal suture)
- posteriorly with the occipital bone (→ lambdoid suture)
- laterally it comes in contact with the temporal bone (→squamosal suture) and sphenoid bone (→ sphenoparietal suture)
In newborns the parietal bones are relatively thin and have an osseous growth center at each of the four corners of the bone. Until approximately 25-30 months of age it becomes completely intramembranously ossified.
The parietal bones are found on both sides of the neurocranium and have two surfaces: an internal and an external one. The internal surface is covered with grooves for the meningeal artery, sigmoid sinus and superior sagittal sinus. The external surface features the superior and inferior temporal lines, together with the parietal foramen.
The borders of the parietal bones include:
- the opposite parietal bone
- the frontal bone anteriorly
- the occipital bone posteriorly
- the temporal and sphenoid bones laterally