Śatapatha Brāhmaṇa ("of a hundred paths") 4.2.1.19

4.2.1.19

tau jaghanena yūpamaratnī saṃdhattaḥ | yadyagnirnodbādheta yadyu agnirudbādhetāpyagreṇaiva yūpamaratnī saṃdadhyātāṃ saṃjagmāno divā pṛthivyā śukraḥ śukraśociṣetyevādhvaryuḥ saṃjagmāno divā pṛthivyā manthī manthiśociṣeti pratiprasthātā cakṣuṣorevaite āramaṇe kurutaścakṣuṣī evaitatsaṃdhattastasmādime abhito 'sthinī cakṣuṣī saṃhite

They put their elbows together behind the sacrificial stake, unless the fire should blaze up; but. if the fire blaze up, they may join their elbows in front of the stake,--the Adhvaryu with, 'The Sukra (bright), uniting with the sky, with the earth, with the brightly shining;' the Pratiprasthâtri with, 'The Manthin, uniting with the sky, with the earth, with the manthin-shining.' Thus they make these two (cups) the resting-places of the eyes, and join the two eyes together: whence these two eyes are joined together with bones all round.