Many of them are derived from Egyptian types; others show the influence of Mesopotamian art, or of the hybrid craftsmanship of Phoenicia. The borrowing or imitation of such foreign types may at first sight appear to show even less promise of artistic progress than variations on the old native images; but it is not in its origins, but in its development and perfection that the chief excellence of Greek art is to be found. The types borrowed by sculpture from foreign art are almost exclusively of human form. The monstrous mixed forms in which the deities of Egypt or Mesopotamia often found the expression of their superhuman and mysterious powers do not seem to have appealed to the imagination of the Greeks. Such mixed forms were, indeed, frequently borrowed by early decorative art, and on "Orientalising" vases we constantly find human-headed and bird-headed quadrupeds, usually winged, and human-headed birds. The delight in winged figures generally, which was mainly decorative in early times, also finds its origin in Oriental woven stuffs. Greek sculpture adopted and translated into stone or bronze some of these mixed types--notably the human-headed bird and the human-headed winged lion; these it identified as the Siren and the Sphinx of Greek myth, and associated them with the mysteries of the tomb. To some other forms, that of the Centaur and the Satyr and the Triton, it also gave considerable scope. But all these, if not human, are hardly to be regarded as divine; they are mostly noxious, and, even if benignant, do not attain the rank of gods. Perhaps a nearer approach to divine character is to be found in the river-gods, who are often represented as bulls with human heads or as human with bull's horns; but here, too, we have only to deal with minor deities. No sculptor represented Dionysus in this way, even though he was called "bull-shaped" by poets; nor is the horse-god Posidon even represented as a Centaur. The horse-headed Demeter of Phigalia remains the strange and solitary exception, however we may explain her existence.