Retinal projections in domestic ungulates. I. The retinal projections in the sheep and the pig

Six sheep and 5 pigs were subjected to unilateral eye enucleation; after a 14-day survival period their brains were treated by the Nauta-Gygax and the Klüver-Barrera methods, to determine the distribution of retinal efferents in the primary optic centres. In both the sheep and the pig the retina projects bilaterally to both the dorsal and ventral nuclei of the lateral geniculate body (LGd, LGv), to the medial interlaminar nucleus (MI), to the nucleus of the optic tract (NTO), to the nucleus pretectalis posterior (PRp), and to the colliculus superior (SC). A concealed type of lamination was found to exist in the LGd of both species. In the LGv, preterminal degeneration was found in the lateral sector only. This nucleus is relatively larger in the pig than in the sheep. In the NTO degenerating preterminals were found to be diffusely distributed, while in the PRp they appeared in the dorsal part of the nucleus only. No degenerating preterminals were found in the pulvinar, the nucleus pretectalis anterior (PRa) or the area pretectalis medialis (PRm). In both species a crossed accessory optic tract corresponding to the posterior fibres of the superior fasciculus of Hayhow could be identified, and the degenerating fibres of this bundle could be treced to the dorsal and the lateral terminal nuclei of the accessory optic system (DTN, LTN). No evidemce of a retinohypothalamic projection was found in either species.