They told him the way, and, moreover, they gave him a mist-cap helmet from Tartarus, which would make him invisible whenever he put it on, and also a bag, which he slung on his back; and, thus armed, he went further to the very bounds of the world, and he took his mirror in his hand, and looked into it.  There he saw the three Gorgon sisters, their necks covered with scales like those of snakes (at least those of two), their teeth like boar’s tusks, their hands like brass, and their wings of gold; but they were all fast asleep, and Perseus, still looking into his mirror, cleft Medusa’s neck with his all-cutting sword, and put her head into the bag on his back without ever seeing her face.  Her sisters awoke and darted after him; but he put on his helmet of mist, and they lost him, while he fled away on Mercury’s swift-winged sandals.  As he sped eastward, he heard a voice asking whether he had really killed the Gorgon.  It was Atlas, the old heaven-supporting giant; and when Perseus answered that he had, Atlas declared that he must see the head to convince him.  So Perseus put a hand over his shoulder, and drew it up by its snaky hair; but no sooner had Atlas cast his eyes on it than he turned into a mountain, his white beard and hair becoming the snowy peak, and his garments the woods and forests.  And there he still stands on the west coast of Africa, and all our modern map-books are named after him.