Schematic of visual pathways in three types of vertebrates: Axonal routing in the optic chiasm is likely to be a reversible process in evolution influenced by the adaptive value of supervising body movements. (a) Optic pathways in limbless vertebrates*. Snakes and caecilians have developed reduced hemispherical specialization for visually guided steering of the body, and relatively high proportions of ipsilateral retinal projections, similar to phylogenetically less advanced, limbless, vertebrates e.g. cyclostomes . The filled circles represent the superior colliculus (SC). Each hemisphere receives information from both visual hemifields. The SC is a component of the tectum, which integrates visual, somatosensory, and auditory information. It is the mammalian equivalent of the optic tectum in amphibians, reptiles, and birds . (b) Optic pathways in a vertebrate with lateralized visual fields and laterally placed forelimbs*. In animals with this anatomy, including the majority of dextropods with limbs, the hemispheres receive practically all, information from the contralateral visual hemifield. The dominance of contralateral retinal projections (CRP) will reduce the need for inter-hemispheric connections, since visual, motor, tactile, and proprioceptive (ViMoTaPro) information concerning the forelimb are processed in the contralateral hemisphere. Thus, when primitive limbless vertebrates began to develop limbs, evolutionary change towards more CRP is likely to have boosted the lateralization of visually guided limbs. (c) Optic pathways in a primate*. Due to the architecture of the OC, the hemispheres of primates** receive visual information solely from the contralateral visual hemifield. In species using forelimbs frontally, modification toward ipsilaterality in the temporal retina is associated with corresponding ViMoTaPro areas localized in the same hemisphere. (Only neural pathways to the SC and primary visual cortex are demonstrated). *The rectangles represent portions of the left and right visual hemifield. **Some other animals such as cats, arboreal marsupials, and fruit bats have similar visual systems.