([3.]) Nasals changed their place of articulation to that of the following consonant. Thus, dental n before the labials p and b became labial m: as, imbibō, I drink in, impendeō, I hang over. Labial m before the gutturals c and g became guttural n ([62]): as, prīnceps, leader, singulī, severally (the original labials appear in prīmus, semel ([138])); hunc for *homce ([662]). Labial m before the dentals t, d, s became dental n: as, cōnsecrō, I consecrate, from com (cum) and sacrō; tantus, so great, from tam; quondam, once, from quom; tandem, at length, from tam. But sometimes the etymological spelling was retained: as, quamdiū, as long as. But m does not change to n before t or s in the inflection of verbs and nouns, where mt, ms develop into mpt, mps ([167]): as, sūmptus, sūmpsī, from sūmō.
([4.]) p and b before n changed to m: as, somnus, sleep, for *sop-nus (cf. sopor); omnis, all, for *op-nis (cf. opēs); Samnium, for *Sabnium (cf. Sabīnī).
([5.]) m before unsyllabic i (i̭) became n: as, quoniam (with vocalic i; [153, 4]), since, for *quoni̭am from quom iam ([1882]); coniungō, I join together, for *comiungō.
([6.]) c between n and l, and before m, changed to g: as, angulus, corner, with anaptyctical ([172]) vowel u for *anglus, from *anclus (cf. ancus); segmentum, section, from the stem sec- in secāre.
[165]. It appears that at a very early period the neighbourhood of a nasal changed an unvoiced mute into a voiced one: as, ē-mungō, I clean out, by the side of mūcus; pangō, I fix, by the side of pāc- in pāx, peace (gen. pāc-is).
[166]. Entire assimilation. ([1.]) One mute is assimilated to another: thus p or b to c: as, suc-currō, I assist; t or d to c: as, sic-cus, dry (cf. sit-is, thirst), accipiō, I accept; d to g: as, agglūtinō, I glue on; t or d to qu: as, quicquam, anything; t or d to p: as, appellō, I call; quippe, why? ([1690]).
([2.]) A mute is assimilated to a spirant: thus, p to f in officīna, workshop, for *opficīna, syncopated form of *opificīna; d to f: as, afferō, I bring hither; when t is thus assimilated to s the result is ss after a short vowel, and s after a long vowel ([170, 7]) or when final ([171]); as, in the -s- perfects, concussī, I shook, for *concutsī (concutiō, [961]); messuī, I mowed, for *metsuī (metō, [835]); suāsī, I advised, for *suātsī (suādeō, [1000]); clausī, I shut, for *clautsī (claudō, [958]); haesī, I stuck, for haes-sī ([868]) from haerēre, stem haes- ([154]); in the same way possum, I can, for *potsum (cf. pot-est, [752]); prōsum, I am of advantage, for *prōtsum (cf. prōd-esse); legēns, reading, for *legents (from the stem legent-, cf. genitive legent-is). An s is never assimilated to a following t: as, haustus, drained ([1014]), from the stem haus-, present hauriō ([154]). Forms like the rare hausūrus (Verg.) are made after the analogy of dental stems.
([3.]) One spirant, s, is assimilated to another, f: as, difficilis, difficult, differō, I am unlike, from dis and facilis, ferō.
([4.]) A mute is assimilated to a nasal: thus d to m in mamma, woman’s breast, from the stem mad- (cf. madeō, [1006]); rāmus, branch, rāmentum, splinter, from the stem rād- (cf. rādō, [958]) with simplification of the double m after the long vowel. d to n in mercēnārius, hireling, from the stem mercēd-, reward, (for mercennarius, see [133], 1); p to m in summus, highest, from the stem sup- (cf. super). A progressive assimilation of nd to nn belongs to the Oscan dialect, and occurs only very rarely in Latin: as, tennitur (Ter.), distennite (Plaut.) See [924]; [950].
([5.]) One nasal, n, is assimilated to another, m: as immōtus, unmoved. But an m before n is never assimilated: as, amnis, river.