A pretectal projection upon the accessory optic nucleus in the pigeon: an anatomical and electrophysiological study.

Neurons of the nucleus lentiformis mesencephali, the avian homologue of the optic tract nucleus, were retrogradely filled with horseradish peroxidase after injections of the enzyme into the accessory optic nucleus in pigeons. The projection appeared exclusively ipsilaterally, and was confirmed by unitary and evoked potential recordings. Together with previous reports in both birds and mammals, the present study contributes information linking the accessory optic system to the pretectal nucleus of the optic tract and thence to horizontal optomotor mechanisms.