Well, then you have elleboro in the dative OR the ablative. Translating, it'd either be "The insane mind prepares/looks ahead/previews images to hellebore," or, using an ablative absolute, "The insane mind looks ahead/prepares/et caetera by means of hellebore the images." Neither of which make much sense to me considering the next sentence. Unless, of course, the hellebore is allowing the head to preview, in which case its absence could cause the results of the last sentence. But, again, I could be talking out of my arse here.