Jaiminīya Upaniṣad Brāhmaṇa 3.3.2

3.3.2

sa eṣa evoktham
yat purastād avāniti tad etad ukthasya śiro yad dakṣiṇatas sa dakṣiṇaḥ pakṣo yad uttaratas sa uttaraḥ pakṣo yat paścāt [tat] puccham /

This very one is the uktha.
That which breathes forward in front, that is the head of the uktha; that which is to the right is the right wing; that which is to the left is the left wing; that which is behind is the tail.