Note 1586 — BOOK VIII. THE NATURE OF THE TERRESTRIAL ANIMALS.
John Bostock translation
As to the tusks of the elephant, no doubt the opinion of Herodotus, B. iii. c. 97, is correct, that they are teeth, and not horns. They are essentially composed of the same substance with the other teeth, and, like them, are inserted into the jaw, and not into the os frontis, as is the case with horns.—B.