The arts thus practised on the great plateau extended to the most southern limits of the North American continent. The ancient graves of the Isthmus of Panama have been ransacked by thousands in recent years, from the temptation which the gold relics they contain hold out to their explorers. Those include representations of beasts, birds, and fishes, frogs, and other objects, imitated from nature, often with great skill and ingenuity. One gold frog which I examined had the eyes hollow, with an oval slit in front, and within each a detached ball of gold, which appeared to have been executed in a single casting. This insertion of detached balls is frequently met with in the pottery, as well as in the goldsmith’s work of the Isthmus, and is singularly characteristic of a peculiar phase of local art. Human figures, and monstrous or grotesque hybrids wrought in gold, with the head of the cayman, the eagle, and other animals, attached to the human form, are also found in the same graves; but, so far as my own opportunities of observation enable me to judge, the human figure generally exhibits inferior imitative skill and execution to the representations of other animate subjects. But all alike display abundant metallurgic art. Soldering as well as casting was known to the ancient goldsmith, and the finer specimens have been finished with the hammer and graving-tool. Judging from the condition of the human remains found in those huacas of the peninsula, they are probably of a much higher antiquity than the era of Mexican civilisation; and lying as they do in the narrow isthmus between the twin continents, they suggest the probability of a common source for the origin of Peruvian and Aztec arts. But while the Mexicans wrought their ingenious toys, lavished their inexhaustible resources of gold and silver in personal decoration, and adorned their public edifices with scarcely less boundless profusion than the Peruvians, they had learned to some extent the practical value of gold and other metals as a convenient currency. By means of this equivalent for the gold and silver coinage of Europe, the interchange of commodities in the great markets of Mexico was facilitated, and an important step in the progress towards a higher stage of civilisation secured. This metallic currency consisted of pieces of tin cut in the form of a =T= or stamped with a similar character, and of transparent quills filled with gold dust. These were apparently regulated to a common standard by their size: for the use of scales and weights, with which the Peruvians were familiar, appears to have been unknown in Mexico.