Shatapatha Brahmana 8.2.4.19

8.2.4.19

tadyāni varṣiṣṭhāni candāṃsi | ye sthaviṣṭhāḥ paśavastānmadhya upadadhāti madhyaṃ tatprati paśuṃ variṣṭhaṃ karoti tasmānmadhyam prati paśurvariṣṭho 'tha ye vīryavattamāḥ paśavastāndakṣiṇata upadadhāti dakṣiṇaṃ tadardham paśorvīryavattaraṃ karoti tasmāddakṣiṇo 'rdhaḥ paśorvīyattaraḥ

The metres which are longest, and the animals which are biggest, he puts in the middle: he thus makes the animal biggest towards the middle; whence the animal is biggest towards the middle. And the animals which are the strongest he puts on the right side: he thus makes the right side of an animal the stronger; whence the right side of an animal is the stronger.