Further observations on the olivocerebellar projection in the monkey.

The distribution of retrogradely labeled cells in the inferior olive was studied following cerebellar injections of horseradish peroxidase in four experiments in macaque monkeys. The flocculus was found to receive its main projection from the dorsal cap and a minor projection from the medial accessory olive. The uvula receives fibers from the nucleus beta, the dorsomedial cell column and from an area of the medial accessory olive. The paramedian lobule is supplied from the dorsal and ventral lamella of the principal olive and from an area in each of the accessory olives. The findings are considered in the light of our more extensive information of the olivocerebellar projection in the cat and with reference to present knowledge of the longitudinal subdivision of the cerebellum in the cat. In general the principal organization appear to be the same in the cat and the monkey, in spite of some species differences. Thus the olivary area projecting to zone C2 (rostral part of the medial accessory olive) appears to be relatively larger in the monkey than in the cat. The same appears to be the case for the dorsal lamella of the principal olive and its cerebellar projecting zone D (probably zone D1).