Accessory optic projections upon oculomotor nuclei and vestibulocerebellum.

Displaced retinal ganglion cells in birds are the sole source of the retinal projection onto the nucleus of the basal optic root, the main component of the accessory optic system. This nucleus has direct bilateral axonal projections onto the oculomotor nuclear complex, the trochlear nucleus- and folia IXc,d and paraflocculus of the vestibulocerebellum. The cerebellar projection terminates within a superficial band of the granule cell layer adjacent to the Purkinje cell layer as a mossy fiber system. This bisynaptic projection onto oculomotor neurons and the cerebellum may play a functionally distinct and specific role in oculomotor reflexes.