The frontal bone (latin: os frontale) is an unpaired bowl-shaped bone located in the forehead region, which contributes in forming the cranium. The frontal bone lies superior to the nasal bones and anterior to the parietal bones.
Parts of frontal bone
The frontal bone has four parts:
- squamous part,
- orbital part (2),
- nasal part.
The squamous part of the frontal bone is the largest part of the frontal bone which forms the area of the forehead. The squamous part of the frontal bone houses the frontal sinuses, which are separated by a septum and are located above the orbits.
The orbital or horizontal part of the frontal bone forms the roof of the orbit and ethmoidal sinuses. The orbital part consists of two orbital plates separated by a gap - the ethmoidal notch.
The nasal part of the frontal bone is located anteriorly between the two orbital parts of the frontal bone forming part of the roof of the nasal cavity.
Surfaces and landmarks of frontal bone
The frontal bone has an external and an internal surface. Several landmarks and structures can be found on each surface.
The external surface of the frontal bone features:
- frontal eminence (2),
- superciliary arch (2),
- supraorbital margin (2), featuring
- frontal notch (or foramen),
- supraorbital notch (or foramen),
- zygomatic process (2),
- temporal line,
- temporal surface.
The frontal eminence is a round elevation on the frontal bone located above the supraorbital margin on each side of the frontal suture.
The superciliary arch is an elevation on the frontal bone above the upper margin of the orbit. Both superciliary arches are joined together by the glabella.
The glabella is a smooth elevation on the frontal bone, a landmark between the two superciliary arches.
The supraorbital margin is the upper orbital margin of the frontal bone.
The frontal notch (sometimes presenting as frontal foramen) is an opening on each of the supraorbital margins of the frontal bone medial to the supraorbital notch (or foramen). The frontal notch or foramen serves as a passage for the supratrochlear artery and the medial branch of the supraorbital nerve.
The supraorbital notch (sometimes presenting as supraorbital foramen) is an opening presented as a notch or a hole located on each of the supraorbital margins of the frontal bone. The supraorbital notch or foramen is the passage for the supraorbital artery and the lateral branch of the supraorbital nerve. It is also a pressure point for the ophthalmic branch of the trigeminal nerve.
A zygomatic process is a part of a bone which articulates with the zygomatic bone. The zygomatic process of the frontal bone is an extension of the frontal bone lateral to the orbit, and it is the process for articulation with the zygomatic bone.
The temporal line of the frontal bone is the continuation of the line formed by the union of the superior and inferior temporal lines of the parietal bone.
A temporal surface of a bone is a part of a bone, which contributes to the formation of the temporal fossa. The temporal surface of the frontal bone is the external, lateral surface of the frontal bone, lateral from the temporal line of the frontal bone, forming the anterosuperior part of the temporal fossa.
The internal surface of the frontal bone features:
- frontal crest,
- groove for superior sagittal sinus.
The frontal crest is the median ridge on the internal surface of the frontal bone for attachment of the falx cerebri.
The groove for the superior sagittal sinus is a shallow depression on the frontal, parietal, and occipital bones forming a channel for the sagittal superior sinus; its margins come together as it passes downward and become continuous with the frontal crest.