Satapatha Brahmana Part V (SBE44), Julius Eggeling tr. , at sacred-texts.com
13:2:3:11. Now, the gods did not know the Pavamâna 2 at the Asvamedha to be the heavenly world, but the horse knew it. When, at the Asvamedha,
they glide along 1 with the horse for the Pavamâna (-stotra), it is for getting to know (the way to) the heavenly world; and they hold on to the horse's tail, in order to reach the heavenly world; for man does not rightly know (the way to) the heavenly world, but the horse does rightly know it
13:2:3:22. Were the Udgâtri to chant the Udgîtha 2, it would be even as if one who does not know the country were to lead by another (than the right) way. But if, setting aside the Udgâtri, he chooses
the horse for (performing) the Udgîtha, it is just as when one who knows the country leads on the right way: the horse leads the Sacrificer rightly to the heavenly world. It makes 'Hiṅ 1,' and thereby makes the. Sâman itself to be 'hiṅ': this is the Udgîtha. They pen up mares, (and on seeing the horse) they utter a shrill sound: as when the chanters sing, such like is this. The priests’ fee is gold weighing a hundred (grains): the mystic import of this has been explained 2.
304:2 Pavamâna is the name of the pressed Soma while it is 'clarifying.' Hence the first stotra of each of the three Savanas of a Soma-day--chanted after the pressing of the Soma and the drawing of the principal cups--is called Pavamâna-stotra. Whether by the term 'Pavamâna' here the clarifying Soma is alluded to, as well as the stotra--which alone the commentator takes it to mean, and to which the second mention certainly refers--must remain p. 305 doubtful. The commentator, it would seem, accounts for this identification of the Pavamâna-stotra with heaven by the fact that the second day of the Asvamedha is an ekavimsa day (see XIII, 3, 3, 3; Tândya-Br. XXI, 4, 1), i.e. one on which all the stotras are performed in the twenty-one-versed hymn-form; and that the Sun is commonly called 'ekavimsa,' the twenty-first, or twenty-one-fold. The particular chant intended is that of the morning pressing, viz. the Bahishpavamâna, or outside-Pavamâna-stotra, so-called because at the ordinary one-day's Soma-sacrifice, it is chanted outside the Sadas. But, on the other hand, in the case of Ahîna-sacrifices, or those lasting from two to twelve days, that stotra is chanted outside only on the first day, whilst on the others it is done inside the Sadas. An exception is, however, made in the case of the Asvamedha, which requires the morning Pavamâna, on all three days, to be performed in its usual place on the north-eastern part of Vedi, south of the Kâtvâla.
305:1 For the noiseless way of sliding or creeping from the Sadas, and returning thither, and approaching the different Dhishnyas, or fire-hearths, see part ii, p. 299, note 2. As has already been stated, it is only after the chanting of the Bahishpavamâna that the victims are driven up to the offering place.
305:2 It is from this, the principal part of the Sâman, or chanted verse (cf. part ii, p. 310, note), that the Udgâtri takes his name; this particular function of his being, on the present occasion, supposed to he performed by the whinnying of the horse. After this they make the horse step on the chanting-ground, apparently either as a visible recognition of the part it has been made to play, or because the horse thereby is made to go to heaven with which the Bahishpavamâna was identified.
306:1 On the mystic significance of this ejaculation (here compared with the neighing of the horse) in the sacrifice, and especially in the Sâman, see I, 4, 1, 1 seqq.; II, 2, 4, 12.
306:2 XII, 7, 2, 13.