Location and Boundaries
The supraorbital margin represents the inferior boundary of the external surface of the frontal bone (Facies externa). Laterally, it continues into the zygomatic process (Processus zygomaticus).
In relation to other skull structures, the margin occupies the following position:
- Inferiorly: It forms the upper border of the orbital opening (Aditus orbitalis), which serves as the base of the pyramidal orbital cavity (Cavitas orbitalis).
- Superiorly: Positioned above the margin are the superciliary arches (Arcus superciliares), which vary in prominence, and the frontal tubers (Tubera/Eminentiae frontales).
- Within the bone: The air-filled frontal sinus (Sinus frontalis) is typically located within the squama of the frontal bone directly above the Margo supraorbitalis.
What Passes Through the Supraorbital Margin?
The medial half of the margin features anatomical structures (notches or foramina) through which the orbit communicates with the facial region. The following structural variations are possible:
- Supraorbital notch or foramen (Incisura/Foramen supraorbitale) — the exit site for the supraorbital vessels and nerve (a., v. et n. supraorbitalis). These vessels originate from the ophthalmic artery (a branch of the internal carotid), and the nerve comes from the frontal nerve (V1, first branch of the trigeminal nerve). The bundle hooks over the margin at the junction of its medial and middle thirds. Important topographical feature: the nerve always lies medial to the vessels.
- Frontal notch or foramen (Incisura/Foramen frontale) — located closer to the glabella. This transmits the supratrochlear vessels and nerve (a., v. et n. supratrochlearis), which share the same origins (ophthalmic artery and frontal nerve). On the skin, they project at the intersection of the supraorbital margin with a vertical line drawn through the medial palpebral commissure.
Role in Topographical Anatomy
The supraorbital margin is a key bony landmark of the head, used to establish anatomical boundaries and projection lines:
- Boundary between the cranial vault and base: The line dividing the neurocranium into the vault (fornix) and base (basis) runs through the frontonasal suture, then along the supraorbital margin toward the superior border of the zygomatic arch.
- Boundary of the vault regions: The margin, together with the glabella, forms the anterior boundary of the frontoparietooccipital region (uniting the first three unpaired regions of the cranial vault).
- Krasnyak/Kroenlein Scheme (Craniocerebral Topography): The upper horizontal line is drawn through the supraorbital margin (parallel to the lower horizontal line passing through the infraorbital margin). The intersection of this upper horizontal with the anterior vertical projects the frontal branch of the middle meningeal artery, and with the posterior vertical projects its parietal branch. This line also aids in mapping the projections of the central (Rolandic) and lateral (Sylvian) sulci of the brain.