The retinofugal fibers and their terminal nuclei in Galago crassicaudatus (primates)

Control and experimental brains of Galago were used to study the subcortical optic nuclei and their retinal input. Weil, Nissl and Fink‐Heimer methods were employed. The pregeniculate nucleus receives predominantly contralateral retinal input. Terminal degeneration is found only in its pars grisea, but not in its pars fibrosa. The lateral geniculate nucleus exhibits seven demonstrable laminae. Laminae 0, 2, 3 and 4 receive ipsilateral retinal input, whereas laminae 1, 5 and 6 receive contralateral input without overlap. In Fink‐Heimer preparations only the ipsilateral lamina 4 and the contralateral lamina 5 show clusters of argyrophilic spherules which probably indicate axo‐dendritic termination of retinofugal fibers. The nucleus praetectalis posterior and nucleus tractus optici receive predominantly contralateral retinal input. In all likelihood, only the stratum griseum superficiale of the superior colliculus receives retionfugal fibers. On the basis of the very remarkable pattern of terminal degeneration, we divide this stratum into substrata A, B and C. The ipsilateral superior colliculus receives retinal input to its substratum B and the contralateral superior colliculus receives retinal input to its substratum A only. Substratum C receives probably no retinal input.