Have a look in a bit more detail here at the roof of the orbit You can see where the optic nerve will eventually appear from the back of the orbit, at the optic canal. There is also a groove in the bone to hold the optic chiasm, where the optic nerves cross over. This is the chiasmatic sulcus. Just note finally that the anterior cranial fossa is bordered posteriorly by the lesser wing of the sphenoid bone