PURPORT

In the Visnu Purana it is stated:

gayatri ca brhaty usnig
jagati tristup eva ca
anustup paṅktir ity uktas
chandamsi harayo raveh

The seven horses yoked to the sun-god's chariot are named Gayatri, Brhati, Usnik, Jagati, Tristup, Anustup and Paṅkti. These names of various Vedic meters designate the seven horses that carry the sun-god's chariot.