Parietal bone anatomy: the paired bones that form the roof and sides of the skull

What it is

A paired, curved bone forming the roof and sides of the skull.

Location

Lies between the frontal bone in front and the occipital bone behind, meeting its partner at the sagittal suture.

Function

Protects the brain.

Body system

Skeletal · paired (left and right)

FMA ID

FMA52789 (Foundational Model of Anatomy)

Key facts

• The coronal, sagittal, lambdoid and squamous sutures border it.
• The pterion lies near its anteroinferior corner.

Clinical relevance

Fracture at the pterion can tear the middle meningeal artery, causing an epidural haematoma.

There are two parietal bones, one on each side. Each forms the superior and lateral wall of the cranium and is part of the neurocranium. Most of each bone forms the calvaria (skullcap) and a smaller part reaches down towards the cranial base. Each is slightly curved and quadrilateral, with two surfaces, four borders and four angles. (Kenhub: Parietal bone.)

In the skull as a whole, the parietal bones form most of the upper lateral side of the skull. Each is bordered by the frontal bone in front, the temporal bone below and the occipital bone behind. (OpenStax Anatomy and Physiology 2e, 7.2: The Skull.)

The sagittal (superior) border is the longest and thickest; here the two parietal bones meet at the sagittal suture. The frontal (anterior) border is the most serrated and forms half of the coronal suture with the frontal bone. The occipital (posterior) border forms half of the lambdoid suture with the occipital bone. The squamosal (inferior) border meets the greater wing of the sphenoid and the squamous and mastoid parts of the temporal bone. (Kenhub: Parietal bone.)

Each parietal bone therefore articulates with five bones: the frontal bone (coronal suture), the greater wing of the sphenoid (at the pterion), the temporal bone (squamous suture), the occipital bone (lambdoid suture) and the opposite parietal bone (sagittal suture). (Radiopaedia: Parietal bone.)

The squamous suture between the parietal and temporal bones starts at the pterion, arches backwards and then continues downwards as the parietomastoid suture. It is often the last major suture to close, and may not fuse completely until about 60 years of age. (Radiopaedia: Squamosal suture.)

The frontal (anterosuperior) angle lies at bregma, where the sagittal and coronal sutures meet. The occipital (posterosuperior) angle lies at lambda, where the sagittal and lambdoid sutures meet, and is the most rounded of the four. The sphenoidal (anteroinferior) angle lies at the pterion. The mastoid (posteroinferior) angle lies at the asterion, where the parietomastoid and lambdoid sutures meet. (Kenhub: Parietal bone.)

The pterion is an H-shaped junction where the parietal, frontal, sphenoid and temporal bones meet. In a pooled analysis of 18,694 skull sides, the typical sphenoparietal pattern, in which the parietal bone meets the greater wing of the sphenoid, was found in about 79% of sides. In a newborn the pterion corresponds to the anterolateral (sphenoidal) fontanelle, which usually closes 3 to 6 months after birth. (Triantafyllou G et al. Unveiling pterion variability: a meta-analytic approach. Surg Radiol Anat 2025.)

The outer surface is smooth and convex. Near its centre is the parietal eminence (parietal tuber), a rounded swelling that you can feel on the side of your head; it marks the site where ossification of the bone began. Two curved lines cross the surface: the superior temporal line, for the temporal fascia, and the inferior temporal line, which marks the upper limit of the temporalis muscle. (TeachMeAnatomy: The Parietal Bone.)

Some people have a small parietal foramen near the sagittal border towards the back. It carries an emissary vein between the scalp and the superior sagittal sinus. Unusually large openings here, called giant parietal foramina, are a recognised anatomical variant. (Radiopaedia: Parietal bone.)

The inner surface is concave and moulded to the cerebral hemispheres. Thin, branching grooves hold the middle meningeal artery and its branches, which supply the dura mater. Along the sagittal border, each bone forms half of a wide groove for the superior sagittal sinus, and the falx cerebri attaches to its edges. (TeachMeAnatomy: The Parietal Bone.)

Small pits called granular foveolae lie beside the groove for the superior sagittal sinus. They contain arachnoid granulations, small outgrowths of the arachnoid mater. (Kenhub: Parietal bone.)

The parietal bone forms by intramembranous ossification, directly in membrane without a cartilage model. Ossification begins at around the eighth week of fetal development at the parietal eminence and spreads outwards, so the edges of the bone are the last parts to ossify. (TeachMeAnatomy: The Parietal Bone.)

In a newborn the corners of the parietal bones border the fontanelles. The anterior fontanelle, the largest, sits at the junction of the coronal and sagittal sutures and usually persists until about 18 to 24 months, when it becomes bregma. (Radiopaedia: Anterior fontanelle.)

The posterior fontanelle, at the junction of the sagittal and lambdoid sutures, is triangular and closes at about 2 to 3 months, when its site becomes lambda. (Radiopaedia: Posterior fontanelle.)

The middle meningeal artery lies immediately deep to the pterion, between the skull and the dura mater. A fracture here can tear the artery, and arterial blood then collects in the extradural space, forming a rapidly expanding haematoma that raises intracranial pressure. The classic history is a lucid interval followed by neurological deterioration. Treatment needs urgent imaging and surgical evacuation. (TeachMeAnatomy: The Parietal Bone.)

Premature fusion of the sagittal suture between the two parietal bones is the most common form of craniosynostosis, accounting for about half of cases. It restricts growth from side to side, so the head becomes long and narrow (scaphocephaly). (Radiopaedia: Craniosynostosis.)

The nearest named structures in the 3D model, measured from the centre of each part:

• Supramarginal gyrus · nervous
• Postcentral gyrus · nervous
• Precentral gyrus · nervous
• White matter of cerebral hemisphere · nervous
• Lateral ventricle · nervous
• Posterior part of superior temporal gyrus · nervous
• Cingulate gyrus · nervous
• Angular gyrus · nervous
• Thalamus · nervous
• Fornix of forebrain · nervous