xviii CONTENTS 



THE WING A TWISTED LEVER OR HELIX— ITS MODE OF ACTION IN THE INSECT, &c. 



PAGE 



§§ 389-391. Arrangement for Moving the Wings of Insects — Speed Attained by Insects — The Centre of 



Gravity in Insects — Articulation of the Wing to the Body of the Insect 1225 



When the Body of the Volant Animal is Fixed and its Wings are made to Vibrate they 



Describe the Figure-of-8 Trajectories in the Air . 1227 



When the Body of the Volant Animal is Advancing and its Wings are made to Vibrate they 



describe first Looped and then Waved Tracks in Space . 1228 



§ 392. Mode of Investigation pursued by the Author 1228 



§ 393. The Muscles and Joints of the Wing . . .1228 



§§ 394-395. Mechanical Theory of the Action of the Insect's Wing as Stated by Chabrier — Objections to the 



Mechanical Theory of Wing Movements . . . 1229 



§ 396. Method of Demonstrating the Accuracy of the Figure-of-8 Movements made by all Wings . . 1230 

 §§ 397-398. Flight of the Common House-fly as seen in the Living Insect — ^FUght of the Crane-fly under 



similar Conditions ... . . 1230-1231 



THE WINGS OF BIRDS 



§§ 399-401. Structure and General Appearance presented by the Wing of the Bird — Movements of the Wing of 

 the Bird — Flexion and Extension of the Wing — Valvular Action of the Primary and Secondary Feathers 

 of the Wing — Muscles, Bones, Joints, Elastic Structures, &c., of the Wing . . 1238-1247 



§ 402. Dimensions and Weights of Important Parts of the Pigeon (Columba livia) . 1249 



§ 403. Consideration of the Forces which propel the Wings of Birds and Bats . . . 1251 



§§ 404-406. Lax Condition of the Shoulder-Joint in Birds and Bats — The Wing Flexed and partly Elevated by 

 the Action of Elastic Ligaments — The Nature and Position of such Ligaments in the Pheasant, Snipe, 

 Crested-Crane, Swan, &c. — The Elastic Ligaments more highly Differentiated in Wings which are 

 made to Vibrate rapidly 1251-1252 



§ 407. Power of the Wing, to what Owing . 1253 



§§ 408-409. The Skeleton or Osseous System of the Bird (Golden Eagle)— The Bones of the Wing of the Bird— 



Their Articular Surfaces, Movements, &c. . ... 1253-1255 



THE MOVEMENTS PECULIAR TO THE SHOULDER, ELBOW, WRIST, AND OTHER 



JOINTS IN THE WING OF THE BIRD 



§§ 410-416. Shoulder-Joint, Elbow-Joint, Wrist-Joint — The Elbow, Wrist, and Other Joints Alternate and 

 Eeciprocate — Elevation and Depression of the Wing, how caused — The Elbow, Wrist, and other Joints 

 always at nearly Right Angles — Lateral Movements in the Elbow, Wrist, and other Joints 125G-1258 



TRACES OF DESIGN IN THE WING OF THE BIRD— THE ARRANGEMENT OF THE 

 PRIMARY, SECONDARY, AND TERTIARY FEATHERS, &c. 



§ 417. Flexion and Extension of the Wing of the Bird in Flight . . j259 



The Wing Strikes Upwards and Forwards during the Up Stroke, and Downwards and Forwards 



during the Down Stroke ... 2262 



§ 418. Reasons why the Effective Stroke should be delivered Downwards and Forwards . j267 



§ 419. The Wing Acts as an Elevator, Propeller, and Sustainer, both during Extension and Flexion 1267 



