xii Would you like to live to be 100 years of age? Have you ever wondered why life expectancy varies from country to country across the world? Do you want to stay healthy for your entire life, no matter how long you do live? Can loss of hearing, vision, and mental acuity in later life be prevented? Scientists and physicians have been searching for answers to questions about the body’s anatomy and physiology for centuries, and that search continues today. As scientific discoveries increase our knowledge about the human body, the possibilities for living longer and healthier lives are increasing. No matter what your career aspirations—whether you are destined for a career in a medical field or planning to become an artist or start your own business—knowledge about the human body can be very useful to you in terms of both your health and appearance. Many of the lifestyle choices that you make today will affect your body when you reach age 60 and beyond. And with your own knowledge about the human body, you can help influence the health of your family and friends. This textbook will answer numerous questions about the structure and function of the human body that may have crossed your mind. It will spark your curiosity about things you have never thought about. As you discover more and more about the fascinating intricacies of the human body, we believe you will agree with us that the human body is the most interesting topic in all of science. Susan J. Hall Michelle A. Provost-Craig William C. Rose Preface