Comparison of brain structure volumes in insectivora and primates. VIII. Vestibular complex.

Volumes of the vestibular complex (VC) and its four main components (medial, inferior, lateral and superior nuclei; VM, VI, VL and VS) were measured in 28 species of Insectivora, 3 species of Scandentia, 18 species of prosimians, 26 species of non-human simians and in man. The relative size showed a definite tendency to increase 2-4.5 times from Insectivora through simians (expressed by size indices). The highest increase was found in VS, the lowest in VI and, in Pongidae and man, also in VL. The differences are discussed with respect to differences in the locomotory behavior of the various taxonomic groups and to differences in the fiber connections and thus different functions of the various nuclei. Species which exploit a 3-dimensional environment and execute fast and complicated head and body movements have a larger VC than closely related species confined to the ground or which are less skilled leapers. The great increase of the VS may be related to the predominant role of vision in primates, particularly in simians.