The “chestnuts” of the horse have sometimes been compared erroneously to the “pads” on the feet of other animals, and supposed to be survivals of a “pad” in each foot corresponding to the inner of the three toes of the Hipparion. The real representative, in the horse, of the chief pad of the foot of animals which do not (as the horse does) walk on the very tip of the toe, is a little knob called the “ergot.” The diagram, Fig. 13, shows how this ergot corresponds to the chief pad of the three-toed tapir’s foot, and so to that of the dog also. [Illustration: FIG. 13.—Diagram of the under surface of the foot in the dog, tapir, and horse, to show that the horny knob of the horse’s foot, called the “ergot,” corresponds to the central “pad” of the other two.] The absence of living horses, or of any kind of ass or zebra, from the American Continent, when first colonised by Europeans in the sixteenth century, is a very singular fact. For we find a great number and variety of fossil remains of extinct horses in both North and South America. It seems possible that some epidemic disease swept them from the whole Continent not very many centuries before Europeans arrived—for there is evidence in South America of the co-existence there of peculiar kinds of horse with the “Indian” natives. It is even alleged that Cabot, in 1530, saw horses in Argentina, which were the last survivors of the native South American species. And it is also said that the Araucanian Indians of Patagonia have a peculiar breed of ponies, which may be derived in part from a native South American stock. I have never been able to procure a skull of this breed, or any detailed description of it. What is quite certain is that in the great cave of Ultima Speranza, in Patagonia—from which the hairy skin, dried flesh and blood, and unaltered dung as well as the bones, of the giant sloth Mylodon were obtained—a great number of the horny hoofs, and the teeth of a peculiar horse were also found some eight years ago, and are preserved in the Natural History Museum, together with the remains of the giant sloth. The condition of these remains is such that they cannot be many centuries old. The animals appear to have been contemporaneous with an early race of Indians who made use of the cave before the arrival of Europeans. A skull of one and a skeleton of another of the peculiar extinct South American horses (called Onohippidium and Hippidium), which survived until a late period in Patagonia and may possibly have been seen by Cabot, are shown in the Natural History Museum. Their bones are found in the superficial gravel and sand of the pampas.