Satapatha Brahmana Part IV (SBE43), Julius Eggeling tr. [1897], at sacred-texts.com
10:6:4:11. Verily, the dawn is the head of the sacrificial horse 1, the sun its eye, the wind its breath, Agni Vaisvânara (the fire belonging to all men) its open mouth. The year is the body of the sacrificial horse, the sky its back, the air its belly, the earth the under part of its belly, the quarters its flanks, the intermediate quarters its ribs, the seasons its limbs, the months and half-months its joints, the days and nights its feet, the stars its bones, the welkin its flesh, the sand its intestinal food, the rivers its bowels, the mountains its liver and lungs, the herbs and trees its hair, the rising sun the forepart, and the setting sun the hindpart of its body, the lightning its yawning, the thundering its whinnying, the raining its voiding urine, and speech its voice. The day, indeed, was produced as the Mahiman 2 (cup) before the horse, and its birthplace is in the eastern sea. The night was produced as the Mahiman (cup) behind (or after) it, and its birth-place was in the western sea: these two Mahiman (cups), indeed, came to be on both sides of the horse. As Haya (steed) it carried the gods, as Vagin (racer) the Gandharvas, as Aryan (courser) the Asuras, as Asva (horse) men. The sea, indeed, is its kindred, the sea its birth-place.
401:1 That is, of Pragâpati, in the form of a horse. For this and the next chapters see the beginning of the Kânva recension of the Brihad-âranyakopanishad.
401:2 This is the name of two gold cups used at the Asvamedha; cf. XIII, 2, 11, I seq.; 5, 2, 23.