170. The s

a. The स् s, as already noticed (145), becomes visarga before a pause.

b. It is retained unchanged only when followed by त् t or थ् th, the surd mutes of its own class.

c. Before the palatal and lingual surd mutes—च् c and छ् ch, ट् ṭ and ठ् ṭh—it is assimilated, becoming the sibilant of either class respectively, namely श् ç or ष् ṣ.

d. Before the guttural and labial surd mutes—क् k and ख् kh, प् p and फ् ph—it is also theoretically assimilated, becoming respectively the jihvāmūlīya and upadhmānīya spirants (69); but in practice these breathings are unknown and the conversion is to visarga.

Examples are: to b. tatas te, cakṣus te; to c. tataç ca, tasyāç chāyā; pādaṣ ṭalati; to d. nalaḥ kāmam, puruṣaḥ khanati; yaçaḥ prāpa, vṛkṣaḥ phalavān.