7.1D: Orbits
- Locate the orbits in the skull
The orbit, or eye socket, is the cavity located in the skull in which the eye and its associated appendages are housed. The orbits are conical, sometimes described as four-sided pyramidal, cavities that open in the midline of the face and point backwards. To the rear of the orbit, the optic foramen opens into the optical canal through which the optic nerve and ophthalmic artery pass.
The primary functions of the orbit include protection of its delicate contents and, through muscle attachment and a smooth coating fascia, to also promote the smooth, delicate movements of the eye.
Structure of the Orbit
The orbital cavity is formed from seven bones. The frontal bone forms the superior border of the orbital rim and also the superior wall (roof) of the orbital surface.
The zygomatic bone forms the lateral (and half of the basal) border of the orbital rim, and also the lateral wall of the orbital surface—this is the thickest region of the orbit as it is most exposed to external trauma.
Completing the basal and medial border of the orbital rim is the maxillary bone, which also forms the inferior wall (floor) of the orbital surface.
The lacrimal and ethmoid bones contribute to the medial wall of the orbit and also to the medial wall of the orbital canal. The small palatine bone contributes to the floor of the orbit.
Finally, the sphenoid bone forms the posterior wall of the orbit and also contributes to the formation of the optic canal.
Key Points
- The orbits are conical or four-sided pyramidal cavities, which open into the midline of the face and point backwards.
- To the rear of the orbit the optical foramen opens into the optic canal, which transmits the optic nerve and opthalmic artery.
- The orbit protects the eye from mechanical injury and provides access for the optic nerve to the brain.
Key Terms
- optic canal : The canal that transmits the optic nerve and ophthalmic artery into the orbital cavity.
- orbit : The bony cavity containing the eyeball; the eye socket.