Verily Day arose after the horse as the (golden) vessel, called Mahiman (greatness), which (at the sacrifice) is placed before the horse. Its place is in the Eastern sea. The Night arose after the horse as the (silver) vessel, called Mahiman, which (at the sacrifice) is placed behind the horse. Its place is in the Western sea. Verily, these two vessels (or greatnesses) arose to be on each side of the horse. As a racer he carried the Devas, as a stallion the Gandharvas, as a runner the Asuras, as a horse men. The sea is its kin, the sea is its birthplace.
In plain words: Day and night came after the horse, like a gold bowl set in front of it and a silver bowl set behind it at the sacrifice, linked to the eastern and western seas. The horse carried gods, heavenly singers, demons and humans, and the sea is where it came from.