(iii.) In the 2nd century A.D., Lat. v (i.e. ṷ) had become a voiced labio-dental fricative, like Eng. v; and the voiced labial plosive b had broken down (at least in certain positions) into the same sound; hence they are frequently confused as in spellings like vene for bene, Bictorinus for Victorinus.
25. (a) Latin s
(i.) became r between vowels between 450 and 350 B.C. (for the date see R. S. Conway, Verner’s Law in Italy, pp. 61-64), as āra, beside O. Lat. āsa, generis from *geneses, Gr. γένεος; eram, erō for *esām, *esō, and so in the verbal endings -erām, -erō, -erim. But a considerable number of words came into Latin, partly from neighbouring dialects, with -s- between vowels, after 350 B.C., when the change ceased, and so show -s-, as rosa (probably from S. Oscan for *rodḭa “rose-bush” cf. Gr. ῥόδον), cāseus, “cheese,” miser, a term of abuse, beside Gr. μυσαρός (probably also borrowed from south Italy), and many more, especially the participles in -sus (fūsus), where the -s- was -ss- at the time of the change of -s- to -r- (so in causa, see above). All attempts to explain the retention of the -s- otherwise must be said to have failed (e.g. the theory of accentual difference in Verner’s Law in Italy, or that of dissimilation, given by Brugmann, Kurze vergl. Gram. p. 242).
(ii.) sr became þr (= Eng. thr in throw) in pro-ethnic Italic, and this became initially fr- as in frīgus, Gr. ῥῖγος (Ind.-Eur. *srīgos), but medially -br-, as in funebris, from funus, stem funes-.
(iii.) -rs-, ls- became -rr-, -ll-, as in ferre, velle, for *fer-se, *vel-se (cf. es-se).
(iv.) Before m, n, l, and v, -s- vanished, having previously caused the loss of any preceding plosive or -n-, and the preceding vowel, if short, was lengthened as in
prīmus from *prismos, Paelig. prismu, “prima,” beside pris-cus.
iūmentum from O. Lat. iouxmentum, older *ieugsmentom; cf. Gr. ζεῦγμα, ζύγον, Lat. iugum, iungo.
lūna from *leucsnā-, Praenest, losna, Zend raoχsna-; cf. Gr. λεῦκος, “white-ness” neut. e.g. λευκός, “white,” Lat. lūceō.
tēlum from *tēns-lom or *tends-lom, trānāre from *trāns-nāre.