[Prisc. Keil. v. I. p. 35.] F multis modis muta magis ostenditur, cum pro p et aspiratione, quae similiter muta est, accipitur.
From the following words of Quintilian we may judge the breathing to have been quite pronounced:
[Quint. XII. x. 29.] Nam et ilia quae est sexta nostrarum, paene non humana voce, vel omnino non voce, potius inter discrimina dentium efflanda est, quae etiam cum vocalem proxima accipit quassa quodammodo, utique quotiens aliquam consonantem frangit, ut in hoc ipso frangit, multo fit horridior.
G, no less than c, appears to have had but one sound, the hard, as in the English word get.
[Mar. Vict. Keil. v. VI. p. 32.] C etiam et g, ut supra scriptae, sono proximae, oris molimine nisuque dissentiunt. Nam c reducta introrsum lingua, hinc atque hinc molares urgens, haerentem intra os sonum vocis excludit: g vim prioris, pari linguae habitu palato suggerens, lenius reddit.
Diomedes speaks of g as a new consonant, whose place had earlier been filled by c:
[Keil. v. I. p. 423.] G nova est consonans, in cujus locum c solebat adponi, sicut hodieque cum Gaium notamus Caesarem, scribimus C. C., ideoque etiam post b litteram, id est tertio loco, digesta est, ut apud Graecos γ posita reperitur in eo loco.
Victorinus thus refers to the old custom still in use of writing C and Cn, as initials, in certain names, even where the names were pronounced as with G.
[Mar. Vict. I. iii. 98.] C autem et nomen habuisse g et usum praestitisse, quod nunc Caius per C, et Cneius per Cn, quamvis utrimque syllabae sonus g exprimat, scribuntur.
H has the same sound as in English. The grammarians never regarded it as a consonant,—at least in more than name,—but merely as representing the rough breathing of the Greeks.