Comparison of brain structure volumes in Insectivora and primates. IX. Trigeminal complex.

Volumes of the trigeminal complex (TR) were measured in 30 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 decrease from 159 in Insectivora to 56 in simians (expressed as size indices). The difference in the development of the TR between Insectivora and Primates is explained by differences in the role of their oro-facial region in exploratory behavior. The largest size was found in semiaquatic Insectivora (average 283). In semiaquatic forms, the reduction of the olfactory centers is compensated by an increase in TR size. The extremely long vibrissae innervated by the trigeminal nerve seem to have a teletactile function in detecting vibrations in the water produced by potential prey.