From a 1933 patent application by Rennie Renfro:
In the sport of greyhound racing, that is enjoyed by dog fanciers and racing enthusiasts, there has been recently introduced, the use of monkey riders, who serve in the capacity of jockeys. Because of the aptitude and imitative tendencies of simians, when they are positioned on the backs of their fleet charges, they imitate the actions of regular jockeys. The employment of the monkey jockey adds considerable zest and enjoyment to the sport. However, as in horse racing, there is always present the danger of the rider being accidentally thrown, and unless some means is provided for safely securing the riders, there is ever present the hazard of the rider being dislodged, with consequent injury.