A reptile has been found with corticaldevelopment intermediate between that of other reptiles and that of mammals. The reptile, a side-necked turtle, shows evidence of considerably more corticothalamic relationships than other reptiles. The usefulness of the side-necked turtle, Podocnemis, is explored in relation to the anatomical substrate for cortical control over lower levels of nervous function. Of the six levels of central nervous system organization in mammals (all six represented individually in different thalamic compartments), there is separate thalamic representation for only some levels in the side-necked turtle. While there are thalamic nuclei in mammals which receive only from the cortex, the side-necked turtle's thalamus possesses only overlapping projections from the cortex and other levels. The significance of the latter for studying the evolution of encephalization is discussed.