Frontal squama
The frontal squama (Squama frontalis) is the unpaired and largest part of the bone.
The external surface (Facies externa) smoothly transitions laterally into the temporal surface (Facies temporalis), and its posterior border is formed by the parietal margin (Margo parietalis). Inferiorly, the surface is bounded by the supraorbital margin (Margo supraorbitalis), which laterally continues into the zygomatic process (Processus zygomaticus).
The medial half of the supraorbital margin has individual anatomical variations:
- It features the supraorbital notch or foramen (Incisura / Foramen supraorbitale), which transmits the supraorbital vessels and nerve.
- Closer to the center (toward the glabella), the frontal notch or foramen (Incisura / Foramen frontale) is frequently present.
Superciliary arches (Arcus superciliares), which vary in prominence, project above the orbital margin, and frontal eminences (Eminentiae frontales) are located above them. Exactly on the midline, right above the root of the nose, lies a smooth area known as the glabella (Glabella).
The internal surface (Facies interna) faces the brain. A sulcus for the superior sagittal sinus (Sulcus sinus sagittalis superioris) descends along the midline from its superior margin. Inferiorly, it narrows and transitions into the frontal crest (Crista frontalis), which serves as the attachment site for the falx cerebri. Lateral to the base of the crest, the foramen caecum (Foramen caecum) is visible, which typically communicates with the nasal cavity and may transmit small veins.
Nasal and orbital parts
The nasal part (Pars nasalis) is the smallest structure of the frontal bone. It is unpaired, located inferior to the squama, and wedged between the two orbital parts. Along the midline, the nasal spine (Spina nasalis) extends inferiorly from it, serving as a support for the nasal septum. Externally, this part is bounded by the nasal margin (Margo nasalis), which articulates with the nasal bones and the frontal processes of the maxillae.
The orbital part (Pars orbitalis) is paired. It forms the superior wall of the orbit via its orbital surface (Facies orbitalis). This surface features two important depressions:
- On the lateral side, near the zygomatic process, lies the lacrimal gland fossa (Fossa glandulae lacrimalis).
- On the medial side lies the trochlear fossa (Fovea trochlearis), where the pulley (trochlea) of the superior oblique muscle of the eye is attached.
Posteriorly, the orbital parts terminate in the sphenoidal margin (Margo sphenoidalis). An open space, the ethmoidal notch (Incisura ethmoidalis), remains between the right and left orbital parts to articulate with the cribriform plate.
Frontal sinus
Because the frontal bone is a pneumatic bone, the frontal sinus (Sinus frontalis) is located within the thickness of its squama (typically directly above the supraorbital margin).
The sinus is divided into two halves by a septum (Septum sinuum frontalium). The shape of the sinuses and the position of the septum vary greatly individually. The cavity is not isolated: it communicates with the nasal cavity via a specific aperture (Apertura sinus frontalis).
Briefly: answers to topical questions
What passes through the foramen caecum of the frontal bone?
The foramen caecum of the frontal bone typically establishes a connection with the nasal cavity and may transmit small veins. Additionally, on the internal cranial base, the foramen caecum connects the anterior cranial fossa with the nasal cavity, transmitting an emissary vein.
Into which nasal meatus does the aperture of the frontal sinus open?
The aperture of the frontal sinus ensures communication between the sinus and the nasal cavity. In turn, on the lateral wall of the nasal cavity, the middle nasal meatus communicates with the anterior and middle ethmoidal air cells, as well as with the frontal and maxillary sinuses.
With which cranial bones does the frontal bone articulate?
The nasal margin of the frontal bone articulates with the nasal bones and the frontal processes of the maxillae.
Specifically, which vessels and nerves pass through the supraorbital notch?
The supraorbital nerve, supraorbital vessels, and vessels and nerves supplying the skin, muscles, and periosteum of the forehead pass through the supraorbital notch or supraorbital foramen.
For the frontal bone, remember "SNS" — Squama, Nasal, and Supraorbital (Orbital) parts.
Class and exam questions
What is located on the supraorbital margin of the frontal bone?
The medial half of the margin contains the supraorbital notch or foramen, as well as the frontal notch or foramen. They serve for the passage of corresponding vessels and nerves.
Which structure on the internal surface of the squama serves for the attachment of the falx cerebri?
The falx cerebri attaches to the frontal crest (Crista frontalis), which is a continuation of the sulcus for the superior sagittal sinus.
Where is the lacrimal gland fossa located?
It is located on the orbital surface (Facies orbitalis) laterally, near the zygomatic process of the frontal bone.
What else to study on this topic
- Variant anatomy of the supraorbital margin foramina and notches
- The connection of the foramen caecum with the venous system of the nasal cavity
- Individual anatomical variability of the frontal sinuses and their septum
- Topography of the articulations between the ethmoidal notch and the ethmoid bone
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