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Abstract Two distinct fiber systems are recognizable in the dorsal lateral geniculate nucleus of the rat. One consists of small bundles running in a transverse plane from the ventrolateral to the dorsomedial parts of the nucleus, and the other is made up of longitudinal fibers which pass approximately antero‐posteriorly through the nucleus parallel to the columns of cells that represent restricted retinal areas (Montero et al., '68). The Nauta method, used after suitable lesions, shows that the transverse bundles carry corticofugal and retinogugal fibers. The former lie mainly in the ventromedial parts of the nucleus and the latter in the dorsolateral parts, but the two groups are also mingled within individual transverse bundles. Both groups send fibers into the lateral geniculate nucleus and each also continues beyond the nucleus. The fibers that ramify in the nucleus leave the transverse bundles and run in the longitudinal system as they break up into a pericelluar plexus. There is evidence that both groups have a terminal distribution along the lines of projection of retinal points. Four days after a lesion within visual area I the degenerating corticogeniculate fibers form a fine plexus limited to the anterior half of the segment that would show retrograde cell degeneration with longer survival times. Seven and 13 days following a cortical lesion the retrograde cell changes obscure the fine corticogeniculate degeneration, but coarse geniculocortical fibers that are undergoing indirect Wallerian degeneration can be seen in the longitudinal system.
Montero et al. (Tue,) studied this question.