Shatapatha Brahmana 10.1.2.7

10.1.2.7

tasya vā etasya jyotiṣṭomasyāgniṣṭomasya trivṛdbahiṣpavamānaṃ tadvratasya śiraḥ pañcadaśasaptadaśā uttarau pavamānau tau pakṣau pañcadaśaṃ hoturājyaṃ saptadaśam pṛṣṭhamekaviṃśaṃ yajñāyajñiyaṃ tatpucam

In this Gyotishtoma Agnishtoma the Bahishpavamâna (stotra) is (in) the Trivrit (stoma)--that is the head of the rite; the two other Pavamânas are (in) the Pañkadasa and Saptadasa (stomas)--they are the two wings; the Hotri's Âgya (stotra) is (in) the Pañkadasa, the Prishtha (stotra in) the Saptadasa, and the Yagñâyagñiya (stotra in) the Ekavimsa (stoma)--they are the tail.