Case pg669, fig3, table1. Soma notes The largest mesencephalic input to the SC arises from the substantia nigra, pars reticularis. Most positive cells were heavily labelled and were located in the rostral half of this structure, without any topographical organization. few in contra. Terminal notes In three cases (Rc14, RC15, RC30), diffusion areas of the enzyme covered much of the dorsoventral extent of the SC. Dark core of the reaction product involved SGI, SAI, SGP and in one case SO, HRP injections.