Parietal BoneEdit

The parietal bones are a pair of large, curved plates that form the roof and the greater part of the sides of the cranial cavity. They safeguard the brain's upper regions, contribute to the overall shape of the head, and provide anchor points for membranes and muscles. Each bone meets its partner along the sagittal suture and connects with several neighboring bones at the margins of the skull, including the frontal bone at the coronal suture, the occipital bone at the lambdoid suture, and the temporal bones at the squamous sutures. The structure of these bones reflects a long history of mechanical requirements—protecting neural tissue while allowing growth and movement of the head—and they are studied not only for their anatomy but for what their variation tells us about development, function, and evolution.

In addition to their protective role, the parietal bones participate in the attachment of soft tissue layers and the accommodation of vascular structures that envelop the brain. The external surface of a parietal bone is generally convex and host to prominent features such as the parietal eminences, which sit roughly at the center and contribute to the bulging contour of the skull. The superior temporal line and inferior temporal line, which run across the external surface, mark the attachment areas for the temporalis muscle and its fascial coverings. On the internal (endocranial) surface, the bones bear impressions and grooves associated with the brain and its membranes, including the grooves that guide the middle meningeal vessels and the midline pathway of the superior sagittal sinus. Small parietal foramina may occur in some individuals, transmitting emissary veins that connect scalp with the veins inside the skull. The parietal bones participate in forming notable landmarks such as the pterion region near the side of the skull, where several bones meet and where structural weakness can influence the pattern of injury in trauma. For more detail on the related skeleton and connections, see the cranium and the neighboring frontal bone, occipital bone, temporal bone, and sphenoid bone.

Anatomy and structure

External surface: The parietal bone presents a broad, dome-like face with the parietal eminences near its center. The temporal lines—superior and inferior—run across the surface and serve as attachment points for the temporalis muscle and the associated fascia.
Internal surface: The inner table is smoother, but carries impressions from the brain and the meningeal coverings. Grooves and foramina may be present where vessels and emissary veins traverse the bone.
Borders and sutures: The bone articulates with the frontal bone at the coronal suture anteriorly, with the occipital bone at the lambdoid suture posteriorly, with the temporal bone at the squamous sutures laterally, and with the opposite parietal bone along the sagittal suture. This arrangement helps distribute mechanical loads during activities such as chewing and head movement.
Notable features: Parietal eminences, temporal lines, and occasional parietal foramina appear in some individuals. Related landmarks include the pterion region—the junction where multiple bones converge on the lateral skull.

Development and variation

The parietal bones arise through intramembranous ossification, the same process that forms many of the flat bones of the skull. Two ossification centers for each bone emerge in early life and fuse as the sutures mature. The sagittal, coronal, lambdoid, and squamous sutures gradually close with age, while fontanelles in infants mark regions where the skull is still growing. The anterior fontanelle and posterior fontanelle involve the frontal and parietal bones as well as neighboring bones during early development. Variability in size, thickness, and the prominence of features such as the parietal eminences occurs across individuals and populations, reflecting biomechanical demands, growth patterns, and genetic ancestry. Modern discussions of skull variation note that such differences do not encode complex attributes like cognitive ability and should be interpreted within a careful, evidence-based framework. See intramembranous ossification and fontanelle for further context, and consider the sutures such as sagittal suture and coronal suture in discussions of skull growth.

Historically, attempts to categorize human groups by cranial form—often drawing on measurements of bones including the parietal—fed into craniometry and, in extreme cases, eugenics. Contemporary science rejects simplistic linkages between skull shape and intellect or racial hierarchy. The debates around these topics are instructive for understanding how scientific methods can be misused when political agendas override evidence. See also craniometry and phrenology in historical perspectives, and the broader discussion of human variation in Homo sapiens.

Function and biomechanics

The parietal bones contribute to the protective enclosure of the brain and form part of the cranial vault’s strength. Their shape helps distribute mechanical loads from impacts and supports the attachment of membranes such as the dura mater. The external features provide anchorage for muscles and fascia, particularly the temporalis muscle, which has implications for jaw movement and bite force. The internal surfaces reflect, in a generalized way, the underlying organization of the brain and its coverings, rather than encoding functional abilities themselves. The integrity of the parietal bones is tested in cases of head trauma, and fractures here can have consequences for intracranial physiology depending on the extent and location of injury.

Clinical significance

Fractures of the parietal bone are a common result of blunt head trauma. While the middle meningeal artery is classically associated with fractures at the pterion region of the skull, any cranial fracture—including those involving the parietal bones—carries a risk of dural injury and intracranial bleeding. Even in the absence of direct vascular injury, parietal bone fractures can be accompanied by brain contusion or concussion. Treatment and prognosis depend on the fracture pattern, associated injuries, and the patient’s neurological status. In some cases, fractures may be accompanied by foramina that connect to venous systems in the scalp, which can influence bleeding patterns. In pathological conditions, the parietal bones can be involved in bone lesions such as osteomas or in developmental variations that require imaging and assessment.

Evolution and comparative anatomy

In humans, the parietal bones contribute to a high, dome-shaped cranial vault that accommodates a relatively large brain and supports upright posture and bipedal locomotion. Comparative anatomy across mammals and primates shows variation in the relative bulk and contour of the skull bones as a function of brain size, feeding mechanics, and habitual head posture. The parietal region can exhibit species-specific patterns of attachment for muscles and membranes, and its development is tied to broader changes in the cranial skeleton that accompany evolution.

See controversies and debates

The history of craniometry and eugenics: early efforts to relate skull shape, including parietal dimensions, to intellectual capacity or social status have been discredited, but they remain a cautionary tale about the misuse of anatomical data. See craniometry and eugenics for historical context, and note how modern science has moved beyond those conclusions.
Modern debates about race and anatomy: some discussions emphasize variation across populations while others caution against drawing hierarchies from skull measurements. The current consensus rejects simplistic racial rankings based on bone shape and instead focuses on genetics, environment, and complex biology. See Homo sapiens and cranial anthropology for related topics.