The cell masses of the diencephalon ofAmphisbaena darwini heterozonata are studied and confronted with those of other reptiles, specially with the burrowing ophidian Typhlopidae. The main differences are in the thalamus dorsalis. The amphisbaenids share with the Typhlopidae the absence of the lateral and pretectal geniculate bodies, and share with the squamate reptiles, differing from the typhlopids, the remaining structures of the dorsal thalamus, characterized by the well-developed nucleus rotundus. These features support the idea that the amphisbaenids could be situated within the Squamata at the same level as in Ophidia and Lacertilia. The adaptive processes toward a burrowing behavior have not been the same in amphisbaenids and in the typhlopids. The causes of the dissimilarities of the dorsal thalamus could be related to other sense and non-sense systems apart from the optic. The morphology of the elements of the cell masses has been studied by the Golgi method.