Volume comparisons in the cerebellar complex of primates. I. Ventral pons.

Volumes of the ventral pons (VPo) were measured in 82 brains of primates, Scandentia, and Insectivora, and the relative size of the VPo was expressed by size indices. The reference line was through the prosimian average; the mean index of prosimians was set at 1. The taxonomic groups arranged in a sequence of ascending mean VPo indices were: Insectivora (0.04), prosimians (1.00), monkeys (2.55), apes (4.48) and man (9.44). Thus, the VPo of man is more than 9 times larger than that of isoponderous average prosimians, and more than 230 times larger than that of isoponderous "basal' insectivores. The indices may reflect trends and extent of VPo evolution in primate phylogeny.