[Head formation in the vertebrates: facts and hypotheses]

One of the most important features of vertebrates is that, as craniates, they have a head. They present some developmental similarities with the cephalochordates, which constitute a brother group of the vertebrates. The amphioxus has a rudimentary brain vesicle, with a frontal single eye. The vertebrates differ by formation of a "new" skull, largely developed from neural crest and placodic cells. At the light of common literature, we discuss here a possible scenario in which an enlargement of the primary neural induction process gives rise to an extension of the forebrain, followed by increased neural crest cell migration.