The Zona Incerta is a key neural substrate of higher brain functions. A neural population in the caudal ZI projects into the superior colliculus. This recently has been identified as a important structure for the saccades. Applying CTb, we describe a retinal projection into the caudal ZI and the distribution of its terminal varicosities in the rock cavy, a Brazilian rodent, which has been used as an anatomical model to enhance the comprehension about the phylogeny of the nervous system. Contrary to other investigated rodents, the retinal fibers in the rock cavy lie in the caudal Zona Incerta (ZIc), suggesting a functional specialization in the rock cavy. The high resolution, and qualitative analysis of retinal fibers in the present work provide a substrate to interpretation of the visual system, and its phylogenetic pathways among species.