[Neurulation continues: the parade commander is...apical constriction]

Neurulation is traditionally defined as the process of closure of the neural tube. New data have shown that the major driving forces ofneurulation continue to operate with the closure of the neural tube, at least until the central canal of the neural tube has formed. Owing to this, the paper proposes to distinguish two periods of neurulation. According to these notions, early neurulation corresponds to the period of closure of the neural tube, and late neurulation corresponds to the period of formation of the central canal. Examples of neural tube defects that affect late neurulation are discussed.