If you grew up with pony books, then you're already familiar with Sam Savitt, one of the great horse illustrators of the 20th century. This book is not only full of his beautiful drawings, but each page includes tips to make your work more accurate. There aren't a lot of words, but the ones that are there add value.
I ordered my copy from his estate (SamSavitt.com); it now appears to be sold out there, but it can be acquired from other sources for a reasonable price.