I love this book, it's one of the most used in my studio. I periodically return to it and either read it or work from it, and each time I find some new subtlety of how our hands are constructed, and how they look.
The detail is incredible - not so much in the pcitures themselves, which can tend toward the sketchy - but in the range, accuracy and depth of observation by the author. Highly recommended.
I have to mention, simply because my fellow reviewer has named it, that I consider this book to be superior to Hogarth's work. Although Hogarth's is still worth owning in addition.