I've noticed that all of the nine Muses except one - Talia - has a circle or sphere incorporated into the image. Does anyone have any thoughts on why she alone would be excluded?
There are eight strings, and eight musical modes; there are eight celestial spheres - the spheres of the seven planets, with the addition of the heaven of the fixed stars, caelum stellatum. But the Muses? What shall be done with the ninth, who would make one too many? This difficulty has long since been resolved: Martianus Capella, who also assigned one celestial sphere to each of the Muses, decreed that Thalia should remain on earth... It is for this reason that Thalia, instead of taking part in the music of the spheres, rests in the lap of the silent and immobile earth."