Frontal bone anatomy: the forehead, supraorbital margin and roof of the orbits

What it is

The bone of the forehead and the roof of the orbits.

Location

Forms the front of the skull, articulating with the parietal bones at the coronal suture and with the sphenoid, ethmoid, nasal, lacrimal, maxilla and zygomatic bones.

Function

Protects the frontal lobes of the brain and forms the upper orbit.

Body system

Skeletal · single, midline structure

FMA ID

FMA52734 (Foundational Model of Anatomy)

Key facts

• Contains the frontal sinuses.
• The supraorbital margin has a notch or foramen for the supraorbital nerve.

Clinical relevance

Frontal fractures can involve the frontal sinus.

The frontal bone is an unpaired, flat, shell-shaped bone that forms the forehead. It curves the forehead, protects the frontal lobes and forms part of the orbit and the anterior cranial fossa. It has six named parts: the squamous part, the nasal part, two orbital plates and two zygomatic processes. (Kenhub: Frontal bone.)

In the skull as a whole it forms the forehead and the glabella, the supraorbital margins with their supraorbital foramina, the brow ridges, the roof of each orbit and the anterior part of the cranial floor. (OpenStax Anatomy and Physiology 2e, 7.2: The Skull.)

The squamous part is the largest. Its convex outer surface forms the forehead and it houses the frontal sinuses. The two orbital parts are triangular, flat plates that form the roof of each orbit. The small nasal part projects downwards between the two supraorbital margins. (TeachMeAnatomy: The Frontal Bone.)

Radiopaedia describes the same bone as a vertical portion (the squama) and a horizontal portion made of two thin orbital plates separated by the ethmoidal notch, into which the ethmoid bone fits. The nasal part ends in a sharp nasal spine that forms part of the nasal septum, and the nasion marks the middle of the frontonasal suture. (Radiopaedia: Frontal bone.)

The supraorbital margin is the curved upper rim of each orbit, where the squamous part meets the orbital part. On it lies the supraorbital foramen (sometimes an open notch instead), which carries the supraorbital vessels and nerve to the forehead. (TeachMeAnatomy: The Frontal Bone.)

A supratrochlear notch or foramen carries the supratrochlear nerve and vessels. Above the margins, the superciliary arches form the brow ridges, which join in the midline at the glabella. Higher still are the frontal eminences, and on each side the zygomatic process projects laterally to meet the zygomatic bone. The upper and lower temporal lines begin here and give attachment to the temporal fascia and the temporalis muscle. (Radiopaedia: Frontal bone.)

The inner surface of the squama is deeply concave. In the midline it carries the sagittal sulcus for the superior sagittal sinus, which narrows below into the frontal crest for the falx cerebri. The foramen caecum is a small notch that may become a foramen carrying an emissary vein from the nose. A groove for the anterior meningeal artery, a branch of the anterior ethmoidal artery, also marks this surface. (Radiopaedia: Frontal bone.)

Each orbital plate has a smooth, concave lower surface that forms most of the orbital roof and a convex upper surface that forms most of the floor of the anterior cranial fossa. The lacrimal fossa for the lacrimal gland lies anterolaterally, and the trochlear fossa for the cartilaginous pulley of the superior oblique muscle lies anteromedially. (Kenhub: Frontal bone.)

The frontal sinuses are paired air spaces in the lower front of the frontal bone, behind the brow ridges, separated by a septum and usually asymmetrical. Each drains from its lower medial corner through the frontal recess into the middle meatus of the nose, either via the hiatus semilunaris or directly. Their blood comes from the supraorbital, supratrochlear and anterior ethmoidal arteries, and their sensation from the supraorbital and supratrochlear nerves. (Radiopaedia: Frontal sinus.)

The frontal sinuses are not present at birth. They begin to pneumatise at about 1 to 2 years of age. One sinus is absent or very small in about 4% of people and both in about 5%, which may be associated with a persistent metopic suture. (Radiopaedia: Frontal sinus.)

The frontal bone articulates with 12 bones: the single ethmoid and sphenoid bones, and the paired nasal, maxillary, lacrimal, parietal and zygomatic bones. At its nasal part it meets the nasal bones and the frontal processes of the maxillae. (TeachMeAnatomy: The Frontal Bone.)

The named sutures are the coronal (frontoparietal) suture with the parietal bones, the sphenofrontal suture with the greater wing of the sphenoid, the zygomaticofrontal suture, the frontonasal suture, the frontomaxillary suture, the frontoethmoidal suture and the frontolacrimal suture. (Kenhub: Frontal bone.)

The frontal bone forms by intramembranous ossification. At birth it is in two halves joined by the metopic (frontal) suture. Sources differ on when this suture closes: Radiopaedia's frontal bone article says it normally fuses in the second year of life, Kenhub gives about 2 years, while Radiopaedia's metopic suture article states that fusion may begin as early as 3 months and is complete in most children by about 9 months. (Radiopaedia: Frontal bone.)

In a small number of adults the suture persists as a vertical line in the midline of the forehead (a persistent metopic suture). It is an anatomical variant of little clinical significance, but on X-rays and CT it can be mistaken for a fracture; its midline position and interlocking edges help tell them apart. (Radiopaedia: Metopic suture.)

Early fusion of the metopic suture (metopic craniosynostosis) gives a triangular forehead, called trigonocephaly. It accounts for about 5% of craniosynostosis cases. (Radiopaedia: Craniosynostosis.)

The glabella and brow (supraciliary) region of the frontal bone is among the most sexually dimorphic areas of the human skull. On average male skulls have a more prominent glabella and brow ridges, while female skulls are smaller and more gracile. The ranges overlap, so these features suggest rather than prove sex. (Del Bove A et al. Mapping sexual dimorphism signal in the human cranium. Sci Rep 2023.)

Frontal sinusitis is inflammation of the frontal sinus, usually caused by infection. If untreated it can spread to cause orbital cellulitis, epidural or subdural abscesses or meningitis. (TeachMeAnatomy: The Frontal Bone.)

Frontal sinus fractures are usually caused by road traffic collisions or falls. A depression of the forehead over the sinus suggests a fracture of its anterior table. Clear fluid leaking from the nose suggests a cerebrospinal fluid leak through a torn dura, which means the posterior table is also broken. (TeachMeAnatomy: The Frontal Bone.)

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

• Medial frontobasal artery · cardiovascular
• Superior frontal gyrus · nervous
• Supra-orbital nerve · nervous
• Supratrochlear nerve · nervous
• Ophthalmic artery · cardiovascular
• Middle frontal gyrus · nervous
• Anterior cerebral artery · cardiovascular
• Anterior commissure · nervous
• Lamina terminalis · nervous
• Frontal nerve · nervous