A Comparative Neuroprimatological Study on the Inferior Olivary Nuclei (from the STEPHAN's Collection)

In 2 species of Tupaiidae, 17 species of prosimians, 12 species of New World monkeys, 10 species of Old World monkeys, Hylobates, Gorilla, Pan and human (the STEPHAN'S collection), volumes of the inferior olivary nuclei (principal-IOPr, accessory-IOAc) were measured. The phylogenetical development was studied by using allometry based upon the regression line of 17 species of prosimians. Volume ratios of IOPr and IOAc to medulla oblongata were also examined.The IOPr evolved progressively from prosimians to human, whereas the IOAc were independent of a general evolutionary trend of primates. The IOAc in great apes and human are far inferior to the average prosimian level. Among the monkeys, the arboreal quadrupedal type develops maintaining a balance between the IOPr and the IOAc in comparison with the semi-brachiation and the Old World terrestrial quadrupedal types. Putting these results together with those of the ventral pons (MATANO et al., 1985b), cerebellar nuclear complex (MATANO et al., 1985a) and the vestibular nuclear complex (MATANO, 1986), some considerations were made in relation with the motor system centering around the cerebellum.