Jaiminīya (Talavakāra) Brāhmaṇa 1.127

1.127

Because Uśanā Kāvya saw it, therefore it is called the Auśana.
It has a final tone.
By means of the tone, food is given to the gods at the end.
At the end of the pavamāna, it equals the verse.
They do not make the sāman exceed the verse, nor the verse the sāman.
When they do not praise in the pavamāna here and here, it is for the sake of the equality of this, for proper arrangement.
Preceded by a tone with the verse-foot, the Gāyatra is in front; preceded by a tone with the verse-foot, it is above at the end of the pavamāna.
Therefore creatures have breaths on both sides, upward and downward.
The Gāyatrī has two sāmans.
It is this downward breath.
Therefore by this breath he performs two actions: he produces feces and he passes wind.
The Bṛhatī has two sāmans.
It is this forward breath.
Therefore by this breath he performs two actions: he discharges semen and he urinates.
The Triṣṭubh has one sāman.
It is the navel itself.
On it is one sāman.
Therefore with this single breath he performs only one action: whatever breath breathes out after breathing in.