This book is a great read to help understand the anatomy and physiology of the swallowing system. It breaks the information down into an easy-to-read format. This is a book that I used extensively when studying for for BCS-S exam and still have the book to reference when I question anatomy or physiology. Definitely worth the money (although you may want to look for it used).
Clinical Anatomy and Physiology of the Swallow Mechanism by Kim Corbin-Lewis, Julie M. Liss and Kellie L. Sciortino