188. Once more, in the Veda

Once more, in the Veda, the same alteration, both of an initial and of a final s, is not infrequent even between the words composing a sentence. The cases are detailed in the Prātiçākhya belonging to each text, and are of very various character. Thus:

a. The initial s, especially of particles; as ū ṣú, hí ṣma, kám u ṣvít;—also of pronouns: as hí ṣáḥ;—of verb-forms, especially from √as: as hí ṣṭhá, diví ṣṭha;—and in other scattering cases: as u ṣṭuhi, nū́ ṣṭhirám, trī́ ṣadhásthā, ádhi ṣṇóḥ, nákiḥ ṣáḥ, yájuḥ ṣkannám, agníḥ ṣṭave.

b. A final s, oftenest before pronouns (especially toneless ones): as agníṣ ṭvā, níṣ ṭe, īyúṣ ṭé, çúciṣ ṭvám, sádhiṣ ṭáva;—but also in other cases, and wherever a final s is preserved, instead of being turned into visarga, before a guttural or labial (171): as tríṣ pūtvā́, ā́yuṣ kṛṇotu, vā́stoṣ pátiḥ, dyāúṣ pitā́, víbhiṣ pátāt.