17 And as for the second beast, he said concerning him that it was like a bear and raised itself up upon one side. Because when the kingdom of Media and Persia arose, it arose in the east. And three ribs were in its mouth. Because the ram was pushing towards the West and towards the North and towards the South, towards three winds of heaven. These three winds it held, and pushed against, like the three ribs that were in the mouth of the bear; until the he-goat came forth from the west, and smote the ram and took out the ribs that were in his mouth.
Source: Demonstrations (New Advent)