What the Bible says about Media, Country of
(From Forerunner Commentary)
Among modern interpreters there is a consensus that the three ribs represent three nations subjugated by the Persians. They also represent the three kingdoms that posed the greatest threat to their power: Lydia, Babylon and Egypt (or some think, Media, Lydia and Babylon). The command to "devour much flesh" emphasizes Persia's superior military might over the peoples from Asia Minor and Egypt to India.
Richard T. Ritenbaugh
Nebuchadnezzar's Image (Part Two): Chest and Arms of Silver