Identifier: animallocomotion00pett (find matches)
Title: Animal locomotion or walking, swimming, and flying : with a dissertation on aëronautics
Year: 1873 (1870s)
Authors: Pettigrew, James Bell, 1834-1908
Subjects: Animal locomotion Physiology Aeronautics
Publisher: London : Henry S. King & Co.
Contributing Library: Yale University, Cushing/Whitney Medical Library
Digitizing Sponsor: Open Knowledge Commons and Yale University, Cushing/Whitney Medical Library

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g)—an upper or dorsal set (fig. 61, d, e,f p. 136), alower or ventral set (c, a, b), and one which is intermediate.This division is intended to refer the feathers to the bones ofthe arm, forearm, and hand, but is more or less arbitrary inits nature. The lower set or tier consists of the primary (b),secondary (a), and tertiary (c) feathers, strung together byfibrous structures in such a way that they move in an out-ward or inward direction, or turn upon their axes, at preciselythe same instant of time,—the middle and upper sets offeathers, which overlap the primary, secondary, and tertiaryones, constituting what are called the coverts and sub-coverts. The primary or rowing feathers are the longest andstrongest (b), the secondaries (a) next, and the tertiaries third(c). The tertiaries, however, are occasionally longer than the PROGRESSION IN OR THROUGH THE AIR. 181 secondaries. The tertiary, secondary, and primary feathersincrease in strength from within outwards, i.e. from the body
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-d ■= rr s *- g ~v s ■ 3 a 5 ~ ° O «= > 2 .03>^_^° _■■§ s>s 5 g-g tffi-J- g-g towards the extremity of the wing, and so of the several setsof wing-coverts. This arrangement is necessary, because the 182 ANIMAL LOCOMOTION. strain on the feathers during flight increases in proportion totheir distance from the trunk. The manner in which the roots of the primary, secondary,and tertiary feathers are geared to each other in order torotate in one direction in flexion, and in another and oppositedirection in extension, is shown at figs. 98, 99, 100, and 101,p. 181. In flexion the feathers open up and permit the airto pass between them. In extension they flap together andrender the wing as air-tight as that of either the insect or bat.The primary, secondary, and tertiary feathers have conse-quently a valvular action. The Wing of the Bird not always opened up to the same extentin the Up Stroke.—The elaborate arrangements and adaptationsfor increasing the area of the wing,

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