β. The Icelandic.—"The numbers from 20 to 100 are formed by means of the numeral substantive, tigr, declined like viðr, and naturally taking the word which it numerically determines in the genitive case.
| Nom. | Fjórir tigir manna | = four tens of men. |
| Gen. | Fjögurra tiga manna | = of four tens of men. |
| Dat. | Fjórum tigum manna | = to four tens of men. |
| Acc. | Fjóra tiga manna | = four tens of men. |
"This is the form of the inflection in the best and oldest MSS. A little later was adopted the indeclinable form tigi, which was used adjectivally."—Det Oldnorske Sprogs Grammatik, af P. A. Munch, og C. B. Unger, Christiania, 1847.
[§ 330]. Generally speaking, the greater part of the numerals are undeclined, even in inflected languages. As far as number goes, this is necessary.
One is naturally and exclusively singular.
Two is naturally dual.
The rest are naturally and exclusively plural.
As to the inflection of gender and cases, there is no reason why all the numerals should not be as fully inflected as the Latin unus, una, unum, unius.