Here are the stone clamps shaped like the letter U, which were put over the wrists and ankles of the victims, to hold them down on the sacrificial stone. They are of hard stone, very heavy and covered with carvings. It is remarkable that, though the altars for human sacrifices are no longer to be found, these accessory stone clamps, or yoke-like collars, are not uncommon. A fine one from Mr. Christy’s collection is figured. _(See opposite page.)_ The obsidian knives and arrow-heads are very good, but these I have spoken of already, as well as of the stone hammers. The axes and chisels of stone are so exactly like those found in Europe that it is quite impossible to distinguish them. The bronze hatchet-blades are thin and flat, slightly thickened at the sides to give them strength, and mostly of a very peculiar shape, something like a T, but still more resembling the section of a mushroom cut vertically through the middle of the stalk. The obsidian mask is an extraordinary piece of work, considering the difficulty of cutting such a material. It was chipped into a rude outline, and finished into its exact shape by polishing down with jeweller’s sand. The polish is perfect, and there is hardly a scratch upon it. At least one of the old Spanish writers on Mexico gives the details of the process of cutting precious stones and polishing them with _teoxalli_ or “god’s sand.” Masks in stone, wood, and terra-cotta are to be seen in considerable number in museums of Mexican antiquities. Their use is explained by passages in the old Mexican writers, who mention that it was customary to mask the idols on the occasion of the king being sick, or of any other public calamity; and that men and women wore masks in some of the religious ceremonies. A fine mask of brown lava (from Mr. Christy’s collection), which has been coloured, is here figured. _(See illustration.)_ The mirrors of obsidian have the same beautifully polished surface as the obsidian mask shows; and those made of nodules of pyrites, cut and polished, are worth notice.