Phorkys married his sister, Keto, and begat a weird offspring enough, the Graiai, Pemphredo, Enyo and Deino, who were grey-haired from birth, and the three Gorgons, Sthenno, Euryale, and Medusa; these strange figures have a part in the legend of Perseus (read the file about the Argosy).
The former are apparently nothing else than old age personified, the spirits of Eld. Their name seems to connect itself with the root of geron (old man) and graus (old woman). It is characteristic of the Greek hatred for uncomeliness that in the text of Hesiod they are called ‘faircheeked,’ an epithet suggesting young and beautiful women, and in art they are shown accordingly with none of the deformities of age. But all accounts agree in making them blind and toothless, or to be exact, as having but one eye and one tooth between the two, or amongst the three, of them. Perseus contrived to steal their eye and tooth, and would not give them back until they gave him in exchange the magic shoes, wallet and cap which he needed; or, according to another version, followed by Aeschylus, he stole the eye only, threw it into Lake Tritonis, and thus left the Gorgons, whose sentries the Graiai were, unguarded, and was able to surprise them.
With regard to the Gorgons, we hear of the head of the Gorgon before anything is told us of the Gorgon herself. The kernel of the myth is, that there existed sometime and somewhere a creature of aspect so terrible that those who saw her turned at once into stone. Homer speaks of the Gorgon most commonly as a decoration and only once as an actual living monster. The older Greek art tallies well with the Homeric passages, for it shows a horrible, grinning head, with flat nose, lolling tongue, and staring eyes, sometimes adding a striding, winged body. With this the descriptions of the poets later than Homer correspond. In particular, several passages give the Gorgons serpents in their hair or girdles, with other monstrous features. This hideous bogey is expanded into the trio, Sthenno (Stheno, Sthenusa; the ‘Mighty One’), Euryale, and Medousa (‘Queen’), of whom the last was mortal. Poseidon was her lover, and when killed by Perseus she was pregnant by him. From her trunk sprang the winged horse Pegasos (it is to be remembered that Poseidon was among other functions a horse-god) and Chrysaor, ‘he of the golden sword.’
There is another tale of Medousa’s death which seems purely Attic. As the armed Athena had a Gorgon-head or gorgoneion on her shield, she was credited with having killed the Gorgon herself, in the battle with the Giants; the two traditions were reconciled by making Perseus slay the Gorgon at Athena’s bidding, and give her the head. A reason was invented for the enmity: Medusa had preferred her beauty above Athena’s. It was supposed that the head was buried under the market-place (Agora) at Athens, and that one lock of it had been given to the city of Tegea, in Arkadia, to protect it. As a result of the Greek hatred of ugliness, or possibly to avoid representing Poseidon as being in love with anything so misshapen as the traditional Gorgon, later art shows Medousa as a beautiful woman; from about 300 b.C. on with a look of terror or pain about the eyes. This last detail is quite late, being part of the realistic art of the third century b.C.; between that time and about the year 400 b.C. or so, Medousa is shown coldly and calmly beautiful.