The Knife presents, both in form and substance, more direct evidence of its Aztec origin; for, in addition to its incrustation with the unique mosaic of turquoise, blended (in this case) with malachite and white and red shell, its handle is sculptured in the form of a crouching human figure, covered with the skin of an eagle, and presenting the well-known and distinctive Aztec type of the human head issuing from the mouth of an animal. (_See cut_, p. 101.) Beyond this there is in the stone blade the curious fact of a people which had attained to so complex a design and such an elaborate ornamentation remaining in the Stone-age; and, somewhat curiously, the locality of that stone blade is fixed, by its being of that semi-transparent opalescent calcedony which Humboldt describes as occurring in the volcanic districts of Mexico—the concretionary silex of the trachytic lavas. The second Mask is yet more distinctive. The incrustation of turquoise-mosaic is placed on the forehead, face, and jaws of a human skull, the back part of which has been cut away to allow of its being hung, by the leather thongs which still remain, over the face of an idol, as was the custom in Mexico thus to mask their gods on state-occasions. The mosaic of turquoise is interrupted by three broad transverse bands, on the forehead, face, and chin, of a mosaic of obsidian, similarly cut (but in larger pieces) and highly polished,—a very unusual treatment of this difficult and intractable material, the use of which in any artistic way appears to have been confined to the Aztecs (with the exception, perhaps, of the Egyptians). The eye-balls are nodules of iron-pyrites, cut hemispherically and highly polished, and are surrounded by circles of hard white shell, similar to that forming the teeth of the wooden mask. The Aztecs made their mirrors of iron-pyrites polished, and are the only people who are known to have put this material to ornamental use. The mixture of art, civilization, and barbarism which the hideous aspect of this green and black skull-mask presents accords with the condition of Mexico at the time of the Conquest, under which human sacrifices on a gigantic scale were coincident with much refinement in arts and manners. The European history of these three specimens is somewhat curious. With the exception of two in the Museum at Copenhagen, obtained many years ago by Professor Thomsen from a convent in Rome, and, though greatly dilapidated, presenting some traces of the game kind of ornamentation, they are believed to be unique. The Wooden Mask and the Knife were long known in a collection at Florence. Thirty years ago the mask was brought into England from that city, as Egyptian: and, somewhat later, the knife was obtained from Venice.