Naturally, as with us, it is more emphatic at the beginning and end of words than in the middle (as, Do not give the tendrils the wrong turn. Is not the sin condemned?)
Priscian says:
[Keil. v. II. p. 29.] N quoque plenior in primis sonat, et in ultimis, partibus syllabarum, ut nomen, stamen; exilior in mediis, ut amnis, damnum.
As in English, before a guttural (c, g, q, x), n is so affected as to leave its proper sound incomplete (the tongue not touching the roof of the mouth) while it draws the guttural, so to speak, into itself, as in the English words concord, anger, sinker, relinquish, anxious.
[Nigidius apud Gell. XIX. xiv. 7.] Inter litteram n et g est alia vis, ut in nomine anguis et angaria et anchorae et increpat et incurrit et ingenuus. In omnibus enim his non verum n sed adulterinum ponitur. Nam n non esse lingua indicio est. Nam si ea littera esset lingua palatum tangeret.
Not only the Greeks, but some of the early Romans, wrote g, instead of n, in this position, and gave to the letter so used a new name, agma. Priscian says:
[Keil. v. II. p. 29.] Sequente g vel c, pro ea (n) g scribunt Graeci et quidam tamen vetustissimi auctores Romani euphoniae causa bene hoc facientes, ut Agchises, agceps, aggulus, aggens, quod ostendit Varro in Primo de Origine Linguae Latinae his verbis: Ut Ion scribit, quinquavicesima est littera, quam vocant “agma,” cujus forma nulla est et vox communis est Graecis et Latinis, ut his verbis: aggulus, aggens, agguilla, iggerunt. In ejusmodi Graeci et Accius noster bina g scribunt, alii n et g, quod in hoc veritatem videre facile non est.
This custom did not, however, prevail among the Romans, and Marius Victorinus gives it as his opinion that it is better to use n than g, as more correct to the ear, and avoiding ambiguity (the gg being then left for the natural expression of double g).
[Mar. Vict. I. iii. 70.] Familiarior est auribus nostris n potius quam g, ut anceps et ancilla et anguia et angustum et anquirit et ancora, et similia, per n potius quam per g scribite: sicut per duo g quotiens duorum g sonum aures exigent, ut aggerem, suggillat, suggerendum, suggestum, et similia.
N before f or s seems to have become a mere nasal, lengthening the preceding vowel.