AbstractIn this work we studied the regional expression pattern of the Enc1 gene in the chick embryo telencephalon at intermediate and late stages of development, bearing on architectonic groupings and boundaries of current interest. In general, the Enc1 signal shows a markedly heterogeneous areal pattern of expression throughout the telencephalon; this corroborates data on new pallial and subpallial structures defined recently in the stereotaxic chick brain atlas of Puelles et al. (2007. The chick brain in stereotaxic coodinates. San Diego, CA: Academic Press). For example: a periventricular/central domain is Enc1‐negative in the ventral pallium or nidopallium; core and shell nuclei appear in the mesopallium; the redefined caudodorsolateral area shows a characteristic pattern; the limits of the densocellular hyperpallium in the dorsal pallium are illuminated; and the postulated entorhinal cortex area is distinct at the posterior telencephalic pole. Interestingly, Enc1 transcripts are distinctly present in the piriform cortex at the surface of the ventral pallium throughout its longitudinal extent, as well as in the most rostral part of the lateral pallium, implying a layout of this cortex more similar to the situation in mammals than was assumed previously. Separate corticoid superficial strata are labeled by the Enc1 probe in the lateral and dorsal pallial regions. In the subpallium, the expression of Enc1 agrees with the new radial subdivisions defined by Puelles et al. (2007). J. Comp. Neurol. 517:564–580, 2009. © 2009 Wiley‐Liss, Inc.