Śaunaka Śikṣā 14

14

akuhāḥ kaṇṭhajāḥ proktā visargaścāpi kaṇṭhajaḥ
tālāvicuyaśā jātā mūrdhanyṛṭuraṣā smṛtāḥ

'a', gutturals, and 'ha' are declared to be produced from the throat; the visarga is also guttural. / 'i', palatals, 'ya', and 'śa' arise in the palate; 'ṛ', retroflexes, 'ra', and 'ṣa' are remembered as retroflex.