This paper reviews and integrates previous research by the authors on the behavioral saliency of the glabrous tail pad and thumbless hand of the spider monkey (Ateles) as organs for tactile exploration of the environment. Observations of laboratory animals in both informal and formal test situations indicate that, although the tail is frequently used in the manipulation and exploration of novel tactile stimuli, the hand is preferred in this respect. Spider monkeys have been successfully taught tactile roughness discriminations using the tail pad as tactile organ, but performance was superior when the hand was utilized.Possible neural correlates of this preference and superiority of the hand over the tail include the following: (a) An increasing superiority of the glabrous hand over the tail pad as the somatic afferent system is ascended (dorsal roots, thalamic ventrobasal complex (Vb), somatic sensory neocortex) with regard to the relative size of single unit or unit cluster cutaneous receptive fields, and (b) a proportionately greater representation of the glabrous hand than the tail pad at both the thalamic and cortical levels.The electrophysiological determination of forelimb and tail dermatomes provided a base line for examination of the organization of the thalamic Vb and the primary somatic sensory cortex (SmI). Both Vb and SmI were found, using microelectrode recording techniques, to be organized in a precise and detailed somatotopic fashion, and it was concluded that it is conceptually more appropriate and parsimonious to characterize the organization of both Vb and SmI as somatotopic, rather than dermatomal.