In the Viṣṇu Purāṇa it is stated:
gāyatrī ca bṛhaty uṣṇig
jagatī triṣṭup eva ca
anuṣṭup paṅktir ity uktāś
chandāṁsi harayo raveḥ
The seven horses yoked to the sun-god’s chariot are named Gāyatrī, Bṛhati, Uṣṇik, Jagatī, Triṣṭup, Anuṣṭup and Paṅkti. These names of various Vedic meters designate the seven horses that carry the sun-god’s chariot.