Exceptions are the following: -
1. Stems in -ón drop n in the nominative: as in legió, stem legi-on-.
2. Stems in din- and gin- drop n and keep an original ó in the nominative: as in virgó, stem virgin-.[These differences depend in part upon special phonetic laws, in accordance with which vowels in weakly accented or unaccented syllables are variously modified, and in part upon the influence of analogy.]
3. Stems in in- (not din- or gin-) retain n and have e instead of i in the nominative: as in cornicen, stem cornicin-. foornote
4. Stems in tr- have -ter in the nominative: as, pater, stem patr-.[These, no doubt, had originally ter- in the stem, but this had become weakened to tr- in some of the cases even in the parent speech. In Latin only the nominative and vocative singular show the e. But cf. Máspitris and Máspiteris (Má[r]s-piter), quoted by Priscan as old forms.]