Śatapatha Brāhmaṇa ("of a hundred paths") 3.3.2.15

3.3.2.15

sa vā udācaṃ nyācam mimīte | sa yadudācaṃ nyācam mimīta imā evaitadaṅgulīrnānājānāḥ karoti tasmādimā nānā jāyante 'tha yatsaha sarvābhirmimīte saṃśliṣṭā iva haivaimā jāyeraṃstasmādvā udācaṃ nyācam mimīte

And, again, as to his meting out in bending them up and down,--he thereby renders them of varied power, and hence these (fingers) are of varied power. That is why he metes out in bending them up and down.