Evolution of the Telencephalon in Nonmammals

Comparative studies of the vertebrate telencephalon began in the late eighteenth and early nineteenth centuries with descriptions of gross mor­ phology (Cuvier 1 809, Owen 1866); however, not until the late nineteenth and early twentieth centuries was the internal anatomy of the telencephalon described for a wide variety of vertebrates (Johnston 1906, Edinger 1908, Ramon y Cajal 1908, Papez 1929, Ariens Kappers et al 1936). This period of intensive study yielded a number of hypotheses regarding the evolution of the vertebrate telencephalon. These hypotheses were based on the anatomy revealed by existing methods-methods that allow what is now referred to as descriptive anatomy-and this anatomy could not be con­ firmed experimentally because the appropriate experimental techniques did not yet exist. In addition, these hypotheses refl ec ted anatomical assump­ tions grounded in scala naturae, which held that vertebrates form one linear series and reflect increasing complexity. The relatively sophisticated armamentarium of neurobiological tech­ niques available today allows us to establish more accurately the anatomy of the telencephalon; these data, data from the fossil record, and a more sophisticated view of vertebrate phylogeny allow us to propose and test new hypotheses regarding the evolution of the vertebrate telencephalon.