In preparing the third edition of this book we have made numerous changes to both the text and illustrations. Many of the changes to the text are to improve accuracy, remove ambiguities, and, we hope, enhance readability, but in the chapters on development and on the nervous system more extensive modifications have been necessary to take account of improving knowledge which stems from the rapidly advancing research in these fields. The changes to the illustrations are mostly of a minor nature and aimed at improving clarity although Fig. 4.24 is completely new. We have been pleased to learn that our textbook is being used by several other groups of students in the health care professions and, at the request of their teachers, we have included appendices on the development of the eye and ear.