Here is a short book covering the details of carving the human face, showing a range of emotions. Though only 64 pages long, it includes details on the muscles of the face and some step-by-step examples of carvings. There are also reference photographs to serve as the basis for your own carvings. The author's obvious skill is enviable.
At about $10 USD new, I think you might want to consider getting the book Carving Facial Expressions
For those more interested in carving caricatures, check out Dave Stetson' book Caricature Carving from Head to Toe
and Pete LeClair's book Carving Caricature Head & Faces
Labels: books, carving, techniques, tips, tools, wood