<P> The optic chiasm or optic chiasma ( / ɒptɪk kaɪæzəm / ; Greek χίασμα , `` crossing '' , from the Greek χιάζω ' to mark with an X ' , after the Greek letter ' Χ ' , chi ) is the part of the brain where the optic nerves partially cross . The optic chiasm is located at the bottom of the brain immediately below the hypothalamus . The optic chiasm is found in all vertebrates , although in cyclostomes ( lampreys and hagfishes ) it is located within the brain . </P>
where does the optic nerve cross the midline ​
optic chiasm