What passes through the optic canal?

Optic nerve and ophthalmic artery

Oculomotor nerve and superior ophthalmic vein

Bones of the orbit

Orbit

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This unit deals with the bones that form the orbit, making the structure of the eye socket clear. On the one hand, the participating bones – frontal, lacrimal, ethmoid, maxilla, sphenoid, palatine and zygomatic – are identified. On the other hand, structures such as the fissures and foramina are explained.

The orbit protects the eyeball together with its muscles, nerves and vessels. Through its openings it communicates with the middle cranial fossa, the pterygopalatine fossa, the nasal cavity and the face. Knowing which bones form each wall and what passes through which opening makes it possible to interpret fractures and nerve deficits in the orbital region.

Key facts

Seven bones form the orbit: frontal, ethmoid, sphenoid, lacrimal, zygomatic, maxilla and palatine.
The orbit is cone-shaped: base = orbital opening, apex = common tendinous ring.
Optic canal: optic nerve and ophthalmic artery.
Superior orbital fissure: cranial nerves III, IV, VI, branches of V1 and the superior ophthalmic vein.
The lamina papyracea and the orbital floor are particularly thin – the floor is the typical site of a blow-out fracture.

Bones of the orbit

Skull from the front with coloured bones; sphenoid, ethmoid and lacrimal bone labelled in the orbit (Gray) — Illustration: Henry Gray, Anatomy of the Human Body (1918), public domain · Highlighting: AnatomyProf

The orbit is formed by seven bones: frontal, ethmoid, sphenoid, lacrimal, zygomatic, maxilla and palatine. They are distributed among the four walls as follows:

Roof: orbital part of the frontal bone, lesser wing of the sphenoid
Medial wall: frontal process of the maxilla, lacrimal bone, orbital plate of the ethmoid, body of the sphenoid
Floor: orbital surface of the maxilla, zygomatic bone, orbital process of the palatine bone
Lateral wall: zygomatic bone, greater wing of the sphenoid

The thinnest parts are the medial wall (lamina papyracea of the ethmoid) and the orbital floor above the maxillary sinus. A blunt blow to the eye therefore typically fractures the floor (“blow-out fracture”); orbital contents and the inferior rectus muscle may herniate into the maxillary sinus, causing double vision. The figure shows the skull from the front; Gray has coloured the bones and, within the orbit, labelled among others the sphenoid (“Sphenoid”), the lamina papyracea of the ethmoid and the lacrimal bone.

Structures of the orbit

Skull from the front with the superior and inferior orbital fissures labelled (Gray) — Illustration: Henry Gray, Anatomy of the Human Body (1918), public domain · Highlighting: AnatomyProf

The orbit has a cone- or pyramid-like shape: the orbital opening (aditus orbitae) forms the anterior opening (base), while the common tendinous ring (anulus tendineus communis) – the shared origin of the four rectus muscles – marks the posterior end (apex).

Optic canal: optic nerve, ophthalmic artery
Superior orbital fissure: oculomotor, trochlear and abducens nerves, branches of the ophthalmic nerve (frontal, lacrimal, nasociliary), superior ophthalmic vein
Inferior orbital fissure: infraorbital and zygomatic nerves (from the maxillary nerve), venous connections to the pterygoid plexus
Anterior and posterior ethmoidal foramina: arteries and nerves of the same name
Zygomatico-orbital foramen: zygomatic nerve

The common tendinous ring encloses the optic canal and the middle part of the superior orbital fissure. Lesions at the orbital apex can therefore damage the optic nerve and the nerves to the eye muscles at the same time (orbital apex syndrome). The figure (skull from the front) carries no colour highlighting; Gray labels the “Superior orbital fissure” and “Inferior orbital fissure” and, on the face, the zygomaticofacial foramen – the outer opening of the canal that begins at the zygomatico-orbital foramen.

Test your knowledge

Multiple-choice questions on structure and function.

Frequently asked questions

Which bones form the orbit?

Seven bones: frontal, ethmoid, sphenoid, lacrimal, zygomatic, maxilla and palatine. The palatine bone contributes only a small orbital process to the orbital floor.

What is a blow-out fracture?

A fracture of the thin orbital floor (less often the medial wall) caused by a sudden rise in intraorbital pressure, e.g. from a fist or a ball. Tissue and the inferior rectus may herniate into the maxillary sinus; typical signs are double vision on upward gaze and numbness in the territory of the infraorbital nerve.

What passes through the superior orbital fissure?

The oculomotor (III), trochlear (IV) and abducens (VI) nerves, the branches of the ophthalmic nerve (frontal, lacrimal, nasociliary) and the superior ophthalmic vein.

Bones of the orbit

Key facts

Bones of the orbit

Structures of the orbit

Test your knowledge

Frequently asked questions

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