brain = the centre of the nervous system; the complicated enlarged anterior end of the spinal cord which directs the activities of the body and which lies in the cranium. The brain develops by dividing into three regions: the prosencephalon (forebrain), the mesencephalon (midbrain), and the rhombencephalon (hindbrain). The adult brain is achieved by division of the forebrain and hindbrain. The prosencephalon divides into the telencephalon (anterior) and diencephalon. The rhombencephalon divides into the metencephalon (anterior) and the myelencephalon. The mesencephalon remains undivided. Details of the brain structure of a fish (Danio rero) may be found in Wullimann et al. (1996).