Jamieson, Fausset and Brown on Genesis 41:17

17. Pharaoh said, In my dream, behold, I stood upon the bank of the river--The dreams were purely Egyptian, founded on the productions of that country and the experience of a native. The fertility of Egypt being wholly dependent on the Nile, the scene is laid on the banks of that river; and oxen being in the ancient hieroglyphics symbolical of the earth and of food, animals of that species were introduced in the first dream.