their utterance, causing its tip to reach the roof of the mouth more easily at a point further back than the dental one.
b. The general Hindu grammar prescribes the same change after a l also; but the Prātiçākhyas give no such rule, and phonetic considerations, the l being a dental sound, are absolutely against it. Actual cases of the combination do not occur in the older language, nor have any been pointed out in the later.
c. The vowels that cause the alteration of s to ṣ may be called for brevity’s sake “alterant” vowels.
181. Hence, in the interior of a Sanskrit word, the dental s is not usually found after any vowel save a and ā, but, instead of it the lingual ṣ. But—
a. A following r prevents the conversion: thus, usra, tiaras, tamisra. And it is but seldom made in the forms and derivatives of a root containing an r-element (whether r or ṛ), whatever the position of that element: thus, sisarti, sisṛtam, sarīsṛpá, tistire, parisrút. To this rule there are a few exceptions, as viṣṭír, viṣṭārá, níṣṭṛta, víṣpardhas, gáviṣṭhira, etc. In ajuṣran the final ṣ of a root is preserved even immediately before r.
b. This dissimilating influence of a following r, as compared with the invariable assimilating influence of a preceding r, is peculiar and problematic.
c. The recurrence of ṣ in successive syllables is sometimes avoided by leaving the former s unchanged: thus, sisakṣi, but siṣakti; yāsisīṣṭās, but yāsiṣīmahi. Similarly, in certain desiderative formations: see below, 184e.
d. Other cases are sporadic: RV. has the forms sisice and sisicus (but siṣicatus), and the stems ṛbī́sa, kīstá, bísa, busá, bṛ́saya; a single root pis, with its derivative pesuka, is found once in ÇB.; MS. has mṛsmṛṣā́; músala begins to be found in AV.; and such cases grow more numerous; for puṁs and the roots niṅs and hiṅs, see below, 183a.
182. On the other hand (as was pointed out above, 62), the occurrence of ṣ in Sanskrit words is nearly limited to cases falling under this rule: others are rather sporadic anomalies—except where ṣ is the product of ç or kṣ before a dental, as in draṣṭum, caṣṭe, tvaṣṭar: see 218, 221. Thus, we find—
a. Four roots, kaṣ, laṣ, bhaṣ, bhāṣ, of which the last is common and is found as early as the Brāhmaṇas.
b. Further, in RV., áṣa, kaváṣa, caṣā́la, cā́ṣa, jálāṣa, pāṣyà, baṣkáya, váṣaṭ (for vakṣat?), kā́ṣṭhā; and, by anomalous alteration of original s, -ṣāh (turāṣā́h etc.), áṣāḍha, upaṣṭút, and probably apāṣṭhá and aṣṭhīvánt. Such cases grow more common later.
c. The numeral ṣaṣ, as already noted (149 b), is more probably ṣakṣ.