<prompt> All of the following form the floor of third ventricle, exceptInfundibulumOcculomotor nerveMammillary bodyOptic chiasma  <response>: Floor of third ventricle is formed from before backward by :Optic chiasmaTuber cinerum infundibulumMammillary bodiesPosterior perforated substanceTegmentum of midbrainRef: Vishram Singh textbook of clinical neuroanatomy second edition pg 137 