Shatapatha Brahmana 13.2.11

Pragâpati desired, 'Would that I were great, and more numerous!' He perceived those two Mahiman (greatness) cups of Soma at the Asvamedha; he offered them; and thereby, indeed, became great and more numerous: hence whosoever should desire to become great, and more numerous, let him offer up those two Mahiman cups of Soma at the Asvamedha; and he indeed becomes great and more numerous.

He offers them on both sides (before and after) the omentum;--the Asvamedha, doubtless, is the Sacrificer, and that Mahiman (cup) is the king: it is with royal dignity he thus encompasses him on both sides. Some gods have the svâhâ-call ('hail') in front, and the other gods have the svâhâ-call behind: it is them he thus gratifies. With 'Hail to the gods!' and 'To the gods hail!' he makes offering by means of the king (Soma) on both sides of the omentum: he thereby gratifies those gods who are in this world, and those who are in the other, and thus gratified, both these kinds of gods lead him to the heavenly world.