Jaiminīya (Talavakāra) Brāhmaṇa 58.308

Agni is the first day; Indra the second; Prajāpati the third; Bṛhaspati the fourth; the Maruts the fifth; the All-Gods the sixth; the Vasus the seventh; the Rudras the eighth; the Ādityas the ninth; Prajāpati is the tenth day. This [earth] is the setting out (prāyaṇa); this is the conclusion (udayana). Therefore yonder Āditya sets from here and rises from here. He travels following this very setting out and conclusion. The swift (āśu) is the trivṛt; the shining (bhānta) is the pañcadaśa; the space (vyoman) is the saptadaśa; the supporter (dharuṇa) is the ekaviṃśa; the force (ojas) is the triṇava; the foundation (pratiṣṭhā) is the trayastriṃśa; the brahman is the caturviṃśa; the kṣatra is the catuścatvāriṃśa; the turning of the clans (vivarto viśām) stoma is the aṣṭācatvāriṃśa; Prajāpati is the tenth day.

Now as to why the trivṛt is 'swift': just as a fast bird is, so is this trivṛt stoma.

Then, as to why the pañcadaśa is 'shining': for that is the kṣatra.

And the kṣatra shines.

Then, as to why the saptadaśa is 'space': for he is Prajāpati.