Although a large body of data about the structure of the central nervous system of cartilaginous fishes has now been accumulated, a systematic survey of the neuromorphology of this, in so many respects, highly interesting group of animals is lacking. The present book is an effort to fill this gap. The information provided is derived partly from the literature and partly from original observations based on our own material. We have attempted to present a complete review of the relevant literature of the last 25 years, but the earlier literature has also been thoroughly scrutinized. Wherever possible we have commented on the functional significance of the various structures. The information available in the literature has been incorporated with our own findings from a detailed study of four species, the sharks Squalus acanthias and Scyliorhinus canicula, the ray Raja clavata and the holocepha- Ii an Hydrolagus collei. Although these species do not reflect the total range of cartilaginous fishes they do exemplify the main features of the major groups.