Parietal bone

Os parietale

One of a pair of curved, four-sided bones that make up most of the roof and side walls of the skull.

At a glance

English: Parietal bone
Latin (TA2): Os parietale
System: Bone
Region: Head
Side: Paired, left and right
Muscles on it: Temporalis

About the parietal bone

There are two parietal bones, a left and a right, and together they form the greater part of the roof and upper side walls of the cranium. Each is a curved, roughly square plate; anatomists describe its outer and inner surfaces, its four borders and its four angles. The pair meet each other along the top of the head; the frontal bone lies in front, the occipital bone behind, and the temporal bone and greater wing of the sphenoid below. The name comes from the Latin for a wall.

The outer surface is smooth and bulges outward. Near its middle is the parietal eminence, the point where bone first formed and usually the widest part of the head. Two arched ridges cross the lower half: the superior temporal line, which holds the temporal fascia, and the inferior temporal line just beneath it, marking the upper limit of the temporalis origin. Above them the bone lies under the tough epicranial aponeurosis of the scalp; beneath them the bone helps to wall the temporal fossa. Towards the back of the upper border a small parietal foramen, when present, lets an emissary vein pass to the superior sagittal sinus.

The inner surface is hollowed to fit the brain and shows the impressions of its folds, together with branching grooves for the middle meningeal vessels that climb up and back from the lower front corner and lower border. Along the top edge a shallow groove pairs with its fellow to make the channel for the superior sagittal sinus, and the falx cerebri attaches to its lips; small pits nearby, deepest in older skulls, hold arachnoid granulations. The borders form four sutures: sagittal with the opposite bone, coronal with the frontal bone, lambdoid with the occipital bone and squamous with the temporal bone, whose thin squama overlaps it. The bregma, where sagittal and coronal sutures meet, and the lambda, where sagittal and lambdoid meet, are the sites of the anterior and posterior fontanelles of the infant skull.

The main clinical point is the middle meningeal artery on the inner surface. A blow to the side of the head, especially near the pterion where the lower front corner meets the frontal, sphenoid and temporal bones, can tear the artery and cause an extradural haemorrhage.

Function and supply

Function: Forms the roof and side walls of the cranial vault over the parietal lobes, and anchors the temporal fascia and the upper part of temporalis.
Nerve supply: Not supplied as a muscle is; the scalp over it is supplied by the supraorbital, auriculotemporal and greater occipital nerves, and the dura beneath by meningeal branches of the trigeminal nerve.
Blood supply: Mainly from branches of the middle meningeal artery running in the grooves on its inner surface, with the superficial temporal and occipital arteries on the outer surface; emissary veins through the parietal foramen link scalp veins with the superior sagittal sinus.

Parts of the parietal bone

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External surface of parietal boneFacies externa ossis parietalisThe smooth, convex outer face of the bone, covered by the scalp. It carries the parietal eminence near its middle and the two temporal lines lower down.
Frontal angle of parietal boneAngulus frontalis ossis parietalisThe front upper corner, close to a right angle, where the sagittal and coronal sutures meet at the bregma. In an infant this is the site of the large anterior fontanelle, which closes in the second year of life.
Frontal border of parietal boneMargo frontalis ossis parietalisThe serrated front edge that meets the frontal bone. With the matching edge of the other side it forms the coronal suture across the top of the skull.
Groove for middle meningeal arterySulcus arteriae meningeae mediaeBranching furrows on the inner surface that fan upward and backward from the lower front corner and lower border. They carry branches of the middle meningeal artery and vein, which can bleed into the extradural space after a fracture.
Inferior temporal lineLinea temporalis inferiorThe lower of the two arched lines on the outer surface. It marks the upper edge of the area from which temporalis arises.
Internal surface of parietal boneFacies interna ossis parietalisThe concave inner face, lying against the dura over the parietal lobe. It shows impressions of the brain's folds, the meningeal grooves and, along its top edge, half of the superior sagittal sinus groove.
Mastoid angle of parietal boneAngulus mastoideus ossis parietalisThe blunt lower back corner. It meets the occipital bone and the mastoid part of the temporal bone, and a broad groove on its inner side holds the bend where the transverse sinus turns down into the sigmoid sinus.
Occipital angle of parietal boneAngulus occipitalis ossis parietalisThe rounded upper back corner, where the sagittal and lambdoid sutures meet at the lambda. In the newborn this point is the small posterior fontanelle, which closes within the first months.
Occipital border of parietal boneMargo occipitalis ossis parietalisThe finely toothed back edge that meets the occipital bone. Together with the matching border of the other side it forms the lambdoid suture.
Parietal eminenceEminentia parietalisThe rounded bulge near the centre of the outer surface, where bone formation began. It marks the widest part of the skull and is easily felt on the side of the head.
Parietal foramenForamen parietaleA small hole, not always present, near the back of the upper border beside the sagittal suture. An emissary vein runs through it, linking scalp veins with the superior sagittal sinus, and a twig of the occipital artery sometimes goes with it.
Sagittal border of parietal boneMargo sagittalis ossis parietalisThe longest and thickest edge, along the top of the bone. Its teeth lock with those of the opposite parietal bone in the sagittal suture.
Sphenoidal angle of parietal boneAngulus sphenoideus ossis parietalisThe thin, pointed lower front corner, wedged into the gap between the greater wing of the sphenoid and the frontal bone. Its outer surface lies at the pterion, and on its inner surface the frontal branch of the middle meningeal artery runs in a deep groove or tunnel.
Squamosal border of parietal boneMargo squamosus ossis parietalisThe lower edge, in three stretches: a short front part covered by the greater wing of the sphenoid, a curved middle part covered by the temporal squama, and a thick back part that interlocks with the mastoid part of the temporal bone.
Superior temporal lineLinea temporalis superiorThe upper of the two arched lines that cross the outer surface. The temporal fascia attaches along it.

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At a glance

About the parietal bone

Function and supply

Related structures

See the parietal bone where it really sits, with every layer of the body around it.