Morphology of geniculo-striate afferents in a prosimian primate

In order to analyze the arborization pattern of single axons innervating layer IV of striate cortex in Galago (a prosimian primate), injections of horseradish peroxidase were made into the white matter below visual cortex. Two distinct fiber types were identified which ramify within different subdivisions of layer IV. Fibers with large axons (type I) have relatively wide terminal arbors which ramify in layer IVa and lower layer III, while those with small axons (type II) arborize in restricted zones of layer IVb. Evidence from previous investigations suggests that terminals of these two fiber types represent the axon terminals of X-like and Y-like geniculate relay cells.