The anatomy of the wrist joint is described in specimens of Ateles geoffroyi, Ateles sp., Lagothrix lagotricha, Pongo pygmaeus and Gorilla gorilla gorilla. It is demonstrated that the semibrachiating monkeys retain a primitive quadrupedal type of articulation with the ulnar styloid process contacting both pisiform and triquetral; the fundamentally different structure of this articulation in Pongidae is confirmed. The implications of these findings for the interpretation of hominoid evolution are briefly discussed.