One thing for its class.
182. The before class nouns may mark one thing as a representative of the class to which it belongs; for example,—
The faint, silvery warblings heard over the partially bare and moist fields from the bluebird, the song sparrow, and the redwing, as if the last flakes of winter tinkled as they fell!—Thoreau.
In the sands of Africa and Arabia the camel is a sacred and precious gift.—Gibbon.
For possessive person pronouns.
183. The is frequently used instead of the possessive case of the personal pronouns his, her, etc.
More than one hinted that a cord twined around the head, or a match put between the fingers, would speedily extract the required information.—Kingsley.
The mouth, and the region of the mouth, were about the strongest features in Wordsworth's face.—De Quincey.
184. In England and Scotland the is often used where we use a, in speaking of measure and price; as,—