M01.02.010 The Frontal Bone

The frontal bone is one of the eight bones that make up the cranium – the superior aspect of the skull that encloses and protects the brain. Its name is derived from the Latin ‘frons,’ meaning ‘forehead.’

In this article, we explore the anatomy of the frontal bone, including its location, structure, and clinical significance.

Anatomical Structure

The frontal bone is an unpaired, shell-shaped bone forming the anterosuperior aspect of the cranium. It consists of four parts: squamous, orbital (x2), and nasal.

Squamous Part

The squamous part is the largest component of the frontal bone, with its external convex surface forming the shape of the forehead.

Features of its Internal Surface:

• Sagittal Sulcus: A vertical groove in the midline of the frontal bone, containing the superior sagittal sinus.
• Frontal Crest: An extension of the sagittal sulcus edges, forming an attachment for the falx cerebri.
• Groove for the Anterior Meningeal Artery.

The squamous part also houses the frontal sinuses. These are separated by a septum and are composed of an anterior and posterior plate. They sit above the orbits on either side of the midline of the face. The supraorbital margin, which separates the squamous part from the orbital part, contains the supraorbital foramen, where the supraorbital vessels and nerve pass through.

Orbital Part

The two orbital parts of the frontal bone are triangular-shaped flat plates that extend posteriorly from the supraorbital margin, forming the roof of the orbit.

When viewed from below, the anterolateral portion consists of the lacrimal fossa (where the lacrimal gland sits), while the anteromedial portion contains the trochlear fossa – an area of attachment for the pulley of the superior oblique muscle.

Nasal Part

The nasal part of the frontal bone is a small area that projects inferiorly between the supraorbital margins. It serves as an area of articulation for the nasal bones and the frontal processes of the maxilla. The nasal spine protrudes from the central portion to support the bridge of the nose.

Attachments

While there is no specific muscular attachment to the frontal bone, the trochlear fossa contains the attachment of a cartilaginous pulley for the superior oblique muscle, named the ‘trochlea’ of the superior oblique muscle. The falx cerebri also attaches to the frontal crest of the internal surface of the frontal bone. The action of the superior oblique muscle is augmented by a cartilaginous pulley that attaches to the frontal bone.

Articulations

The frontal bone articulates with twelve other bones of the skull:

• Unpaired: Ethmoid, Sphenoid
• Paired: Nasal, Maxilla, Lacrimal, Parietal, Zygomatic

Clinical Relevance

Frontal Sinusitis

Frontal sinusitis refers to inflammation of the frontal sinus, usually caused by an infection. It is a relatively common condition. However, if untreated, the infection can spread to surrounding structures in the orbit or cranial cavity, leading to complications such as orbital cellulitis, epidural and subdural abscesses, or meningitis.

Frontal Sinus Fracture

Fractures of the frontal sinus most typically occur from motor vehicle accidents or falls. The characteristic clinical sign is a frontal depression in the anterior table of the skull. Posterior table disruption may be identified by clear fluid leakage from the nose, indicating a cerebrospinal fluid leak due to rupture of the dura mater.

Bibliography

• TeachMeSeries Ltd (2024). Anatomy of the Frontal Bone. TeachMeSeries.