The frontal bone consists of three parts (squamous part, orbital part, and nasal part).
The squamous partor squama (squama frontalis), is the vertical part forming the forehead. It curves downwards and forwards from the calvaria and it has the:
External surface consists of:
Frontal tuber or frontal eminence (tuber frontale) seen as an elevated eminence above the midpoint of the supraorbital margin. They are more prominent in the skulls of the youth and in female adults than in males.
Glabella (glabella)flat area between the medial ends of the eyebrows (superciliary arches).
Superciliary arch (arcus superciliaris) curved and medially prominent (more in males).
Supraorbital margin (margo supraorbitalis) of the orbits. On the medial one-third part of the supraorbital margin are situated the:
- Supraorbital notch (supraorbital foramen) (incisura sive foramen supraorbitale) is situated on each side of the margin, laterally to the frontal foramen. It transmits the supraorbital vesselsand nerve (subdivisions from CN V1).
- Frontal notch (frontal foramen) (sulcus sive foramen frontale) is located medially to the supraorbital foramen.
In the fetal skull, at the midline, we can see a ridge, which represents the metopic suture (sutura metopica)also called as the frontal suture. It is obliterated in adults.
The frontal sinus (sinus frontales), with the septum of the frontal sinuses (septum sinuum frontalium)and the opening of the frontal sinus (apertura sinus frontalis) is located behind the medial end of the supraorbital margin, between the squamous and the orbital part.
The internal surface (facies interna) has the:
Frontal crest (crista frontalis) for attachment of the falx cerebri. It terminates into a small notch and is converted into the:
- Foramen cecum (foramen caecum) by the ethmoid bone. In the clinical jargon it is known as Morand’s or Schwalbe’s foramen.
- Groove for the superior sagittal sinus (sulcus sinus sagittalis superioris) which contains the superior sagittal sinus (venous sinus).
The temporal surface (facies temporalis)has the:
Parietal margin (margo parietalis) articulates with the parietal bone.
Temporal line (linea temporalis) which is curved posterosuperiorly and divides into the superior and inferior temporal line on the squamous part of the temporal bone.
Zygomatic process (processus zygomaticus).
The orbital part (pars orbitalis)is a horizontal componet that partly forms the roof of the orbital cavity. It is a smooth and concave and merges into the orbital surfaces (facies orbitalis). On its inferior surface and within are found the following features:
Fossa for lacrimal gland or lacrimal fossa (fossa glandulae lacrimalis)which is at the anterolateral part of orbital surfaces.
Trochlear fovea (fovea trochlearis) or occasionally trochlear spine (spina trochlearis)which is found below and behind the medial ends of the supraorbital margin.
Anterior ethmoidal foramen (foramen ethmoidale anterius) which is located anteriorly, on the superior margin of the orbital plate of the ethmoid bone. It transmits the anterior ethmoidal nerve and vessels.
Posterior ethmoidal foramen (foramen ethmoidale posterius) which is located posteriorly, on the superior margin of the orbital plate of the ethmoid bone. It transmits the posterior ethmoidal nerve and vessels.
Sphenoidal margin (margo sphenoidalis) connects with the greater wing of the sphenoid bone.
Ethmoidal notch (incisura ethmoidalis) is located between the two orbital parts.
The nasal part (pars nasalis)is a horizontal part forming the roof of the nasal cavity. It has the:
Nasal margin (margo nasalis)
Nasal spine (spina nasalis) forms top of the nasal septum.