Pony Express mochila

A mochila (Spanish, pronounced [mo-chee-lah], for "knapsack", "pack", "pouch") is a removable lightweight leather cover put over a horse's saddle. In the nineteenth century, it was used as a mail bag by the Pony Express. The eighth-of-an-inch leather cover draped over the saddle on a horse. There were slits cut into the leather which allowed the saddle horn and cantle to protrude through.