A cylindrical cellular discontinuity commonly occurs in lateral geniculate layers that are innervated by the contralateral eye. Such a discontinuity has been found in a variety of mammalian species, including carnivores, primates, a rodent and a marsupial. Electrophysiological evidence obtained from some of these species shows that the discontinuity corresponds to the blind spot. It is concluded that the representation of the retina within the lateral geniculate nucleus is extremely accurate, since the retinal receptor layer and the geniculate layers have corresponding holes.
Two possible mechanisms that would demand such a discontinuity are considered. One is an intralaminar mechanism in which the cells in each lamina accurately reflect the distribution of retinal receptors; the other is an interlaminar mechanism in which the representations of the homonymous hemiretinae are so accurately aligned that the optic disc must be represented by a cellular discontinuity.