The Parietal Bone

Anatomical Structure

External Surface

The external surface of the parietal bone is smooth and convex. It is marked by the parietal eminence – a raised area marking the primary ossification centre. This is a rounded swelling easily palpable on the lateral skull.

Two curved ridges cross the external surface of the parietal bone:

• Inferior temporal line – upper limit of the attachment of the temporalis muscle.
• Superior temporal line – upper limit of the attachment of the temporal fascia.

Near the midline, some individuals possess a small parietal foramen – an opening that allows an emissary vein to pass between the scalp and the superior sagittal sinus.

Internal Surface

The internal surface of the parietal bone is moulded to the shape of the cerebral hemispheres – and much of its detail reflects the course of blood vessels and meninges.

A prominent feature are the branching grooves of the middle meningeal artery which supplies the dura mater.

At the midline, the superior border forms half of the sagittal sulcus. Together with the opposite parietal bone, this sulcus houses the superior sagittal sinus- a major dural venous channel. The falx cerebri, a dural fold, attaches along its edges.

By TeachMeSeries Ltd (2025)

Fig 2
The internal surface of the parietal bone.

Borders & Articulations

The parietal bone has four borders, each contributing to a cranial suture:

• Sagittal border – articulates with the opposite parietal bone along the sagittal suture.
• Frontal border – articulates with the frontal bone at the coronal suture. The meeting point with the sagittal suture is called the bregma.
• Squamous border – articulates with the temporal bone and the greater wing of the sphenoid, forming the parietomastoid and sphenoparietal sutures respectively.
• Occipital border – meets the occipital bone at the lambdoid suture. The junction of the lamboid suture with the sagittal suture is known as the lambda.

The parietal bone contributes to the H-shaped pterion. This is an articulation with the temporal, sphenoid and frontal bones on the lateral aspect of the skull, and an area of potential weakness.

By TeachMeSeries Ltd (2025)

Fig 3
The external surface and borders of the parietal bone.

Ossification

The parietal bone forms by intramembranous ossification. This means it develops directly from mesenchymal tissue rather than cartilage.

This process begins around week 8 of foetal development at the parietal eminence. Bone growth spreads outward from this point, with the edges ossifying last.

Clinical Relevance

Extradural Haematoma

The parietal bone articulates with the frontal, temporal, and sphenoid bones at a point known as the pterion. This region is a relative weak spot in the lateral skull, as multiple sutures converge and the bone is thin.

Immediately deep to the pterion runs the middle meningeal artery, which lies between the skull and the dura mater. Trauma to this area can fracture the skull and damage the underlying artery.

Injury to the middle meningeal artery leads to arterial bleeding into the extradural space, causing a rapidly expanding extradural haematoma and raised intracranial pressure. Patients classically develop a lucid interval followed by neurological deterioration, and management requires urgent imaging and surgical evacuation.

By TeachMeSeries Ltd (2025)

Fig 4
Lateral view of the skull, showing the path of the meningeal arteries. Note the pterion, a weak point of the skull, where the anterior middle meningeal artery is at risk of damage.