Amelia, Appendix Quarter Horse Second in the Horse of the Year series, this limited edition Appendix Quarter Horse is exclusively available in 2014! An Appendix Quarter Horse is a cross between a Quarter Horse and Thoroughbred. They have the best of both worlds with the height, speed, and refinement of the Thoroughbred, and the muscle and bone of the Quarter Horse. Versatile riding horses, the Appendix is used for many of the same disciplines as its parent breeds. They are also often seen competing in eventing, barrel racing and English riding events!