The accessory optic system of the wallaby, Setonix brachyurus: anatomy in normal animals and after early unilateral eye removal.

We have traced primary visual projections to nuclei of the accessory optic system in the mature wallaby, Setonix brachyurus, the "quokka," following unilateral intraocular injections of horseradish peroxidase. The organization of pathways and nuclei is similar to that of other marsupials and to that of eutherian mammals. The dorsal, lateral and medial terminal nuclei receive bilateral input, though nuclei ipsilateral to the injected eye are weakly labelled in comparison with their contralateral counterparts. We also report on the accessory optic system in animals which were unilaterally enucleated neonatally or at postnatal day 35. At maturity in enucleated animals, ipsilateral projections to all nuclei of the accessory optic system are more densely labelled than normal. This exuberance is more pronounced in neonatally enucleated animals than in those enucleated at the later stage.