The number of precaudal vertebrae in three African cercopithecine species are analyzed, with two definitions for thoracic and lumbar vertebrae compared. It is found that generic averages obscure some rather substantial differences at the species level for both Cercopithecus and Cercocebus. Further, when zygapophysis structure is used to define vertebral type, rather than presence or absence of rib facets, there is a substantial change in thoracic and lumbar averages that may be important from a functional (locomotion) standpoint.