Note g — BOOK VII.
Reading edition
Mr. Willughby, Ray, and many others, imagine the principal use of the Tail to be to steer, and turn the Body in the Air, as a Rudder. But Borelli hath put it beyond all doubt, that this is the least use of it, and that it is chiefly to assist the Bird in its Ascents and Descents in the Air, and to obviate the Vacillations of the Body and Wings. For as for turning to this or that Side, it is performed by the Wings and Inclination of the Body, and but very little by the help of the Tail.