One of the most important evolutionary innovations of vertebrates is a complexly structured telencephalon,which provides higher forms of nervous activity in animals and humans. This work is devoted tothe study of the appearance of the telencephalon in the early stages of vertebrate evolution. At the same time,there is reason to believe that lampreys, due to their evolutionary antiquity, could retain some ancient expressionpatterns of genes that regulate the development of the brain in the very first vertebrates. The study of thefeatures of spatio-temporal expression patterns of key genes that regulate the development of the forebrain inlampreys compared with other vertebrates can help to understand the molecular mechanisms underlying theappearance and evolutionary development of this unique structure of vertebrates. This paper presents theresults from analyzing the gene-expression dynamics of Lanf, FoxG1, Otx2, Goosecoid, and HoxB9 in the earlystages of development of the European river lamprey Lampetra fluviatilis. It was shown that lamprey genesinvolved in telencephalon differentiation (Lanf and FoxG1) exhibit heterochrony of expression compared withmore evolutionarily advanced representatives of vertebrates. This fact confirms the idea that the telencephalon,being evolutionarily the youngest part of the brain, could appear in vertebrate ancestors as a superstructurein the late stages of their embryonic development.