[329.] Declension of the Cardinals. Of the cardinals only ūnus, duo, trēs, the hundreds above one hundred, and mīlle used as a noun, are declinable.

a. ūnus is one of the nine irregular adjectives, and is declined like nūllus (cf. [§§ 109], [470]). The plural of ūnus is used to agree with a plural noun of a singular meaning, as, ūna castra, one camp; and with other nouns in the sense of only, as, Gallī ūnī, only the Gauls.

b. Learn the declension of duo, two; trēs, three; and mīlle, a thousand. ([§ 479].)

c. The hundreds above one hundred are declined like the plural of bonus; as,

ducentī, -ae, -a
ducentōrum, -ārum, -ōrum
etc. etc. etc.

[330.] We have already become familiar with sentences like the following:

Omnium avium aquila est vēlōcissima Of all birds the eagle is the swiftest Hoc ōrāculum erat omnium clārissimum This oracle was the most famous of all

In such sentences the genitive denotes the whole, and the word it modifies denotes a part of that whole. Such a genitive, denoting the whole of which a part is taken, is called a partitive genitive.

[331.] Rule. Partitive Genitive. Words denoting a part are often used with the genitive of the whole, known as the partitive genitive.

a. Words denoting a part are especially pronouns, numerals, and other adjectives. But cardinal numbers excepting mīlle regularly take the ablative with ex or instead of the partitive genitive.