Optic chiasma

The optic chiasma, or 'optic chiasm',Greek , "crossing", from the Greek  'to mark with an X', after the Greek letter 'Χ', chi is the part of the brain where the optic nerves (CN II) partially cross. The optic chiasm is located at the bottom of the brain immediately below the hypothalamus.Colman, Andrew M. 2006. Oxford Dictionary of Psychology. 2nd ed, Oxford University Press. p530 

Pathways
The images on the nasal (inner) sides of each retina cross over to the opposite side of the brain via the optic nerve at the optic chiasm. The temporal (outer) images, on the other hand, stay on the same side. This allows the images from either side of the visual field to go to the appropriate side of the brain, combining the sides together.

Beyond the optic chiasm, with crossed and uncrossed fibers, optic nerves become optic tracts.

The crossing over of optic nerve fibres at the optic chiasma allows the visual cortex to receive the same hemispheric visual field from both eyes.Eye, human. Encyclopædia Britannica 2006 Ultimate Reference Suite DVD 2009.

The optic chiasma is found in all vertebrates.

 References 

Category:Anatomy of the brain
Category:Vision