Cortical blindness and the functions of the non-geniculate fibres of the optic tracts.

Of the fibres of the human or simian optic tract, the majority run to the lateral geniculate nucleus. This nucleus has other inputs besides the optic tract, but has probably only one output, the geniculo-calcarine tract (Poijak and Hayashi, 1936). A substantial minority of the fibres of the optic tract, 20 to 30 % in man according to Bernheimer (1899), go to other destinations. The largest groups of such non-geniculate fibres end in the superior colliculi and pretectal region, but Pasik and Pasik (1968) have given evidence that those that end in the nucleus paralemniscalis (accessory optic system) may be important visually. At least in the rat (Sefton, 1968), many optic nerve fibres divide and send one branch to the lateral geniculate nucleus and one to