Śatapatha Brāhmaṇa ("of a hundred paths") 8.3.2.9

8.3.2.9

tā vā etāḥ | catasra ṛtavyā madhyamāyāṃ citā upadadhāti dve-dve itarāsu citiṣu catuṣpādā vai paśavo 'ntarikṣam madhyamā citirantarikṣe tatpaśūndadhāti tasmādantarikṣāyatanāḥ paśavaḥ

There are here four seasonal (bricks) he lays down in the middlemost layer; and two in each of the other layers,--animals (cattle) are four-footed, and the middlemost layer is the air: he thus places animals in the air, and hence there are animals that have their abode in the air.