Emissary canals in the hominoidea and their phylogenetic significance.

Two emissary canals of the skull base (the retroarticular and condylar canals) have been examined in a sample of 1,453 great apes. Our results imply that emissary vein patterns are distinct for orang-utans and African apes. In orang-utans the temporal sinus is frequently present and the retroarticular canal is often present. Orang-utans show a different external venous system in which the condylar canal is very rare. In orang-utans the retroarticular canal resembles the more primitive structure in prosimians and is probably homologous with it. In the African apes, as in humans, the temporal sinus regresses and the condylar vein is well developed. The complete absence of a retroarticular canal can be considered as a synapomorphy supporting the human-African ape clade and excluding Pongo. The enlargement of the condylar vein is much more frequent in the common chimpanzee. The dominance of the condylar vein over the temporal sinus appears to occur progressively during great ape evolution.