By integrating experimental evidence in the published literature with our experimental findings we propose that primate cortical neurogenesis can be divided into two stages. During early neurogenesis (left), basal fibers of ventricular radial glia contact the pial surface and newborn neurons migrate along ventricular as well as outer radial glia fibers. During late neurogenesis (right), newborn neurons reach the cortical plate only along outer radial glia fibers. VZ – ventricular zone, NESC – neuroepithelial stem cell, ISVZ – inner subventricular zone, OSVZ – outer subventricular zone, IZ – intermediate zone, SP – subplate, CP – cortical plate, MZ – marginal zone, IPC – intermediate progenitor cell, vRG – ventricular radial glia, tRG – truncated radial glia, oRG – outer radial glia.