446 DP PETIGPEW ON THE PHYSIOLOGY OF WINGS. 



fibrous ligament d, e. The elastic ligament g, i flexes the hand upon the forearm, and the 



ligament r the fingers upon the hand. 

 Figure 23 shows the muscles and elastic ligaments in the wings of the pheasant, as seen on the dorsal 



aspect, the wing to the right of the observer being fully extended, that to his left being 



fully flexed. In the former the elastic ligaments are put upon the stretch ; in the latter, 



they are in a state of contraction. 

 a, b, Voluntary muscular fibres, terminating in fibrous and elastic tissues c and k. These structures 



act in conjunction, and fold or flex the forearm on the arm. 

 / h, Voluntary muscular fibres, sending processes into elastic ligament g ?', to flex the hand upon the 



forearm. The arm is drawn towards the body by the elastic ligament d, and by the 



muscles v, w. 



Plate XVI. 



Figures 24 and 28 show the muscles and elastic ligaments, and the arrangement of the primary and 

 secondary feathers on the ventral and dorsal aspects of the wing of the crested crane. 

 The wing is in the extended condition in both cases. 



a b, Voluntary muscular fibres terminating in elastic band k. This band splits up into two portions 

 (k, m, figure 24). A somewhat similar band is seen at j (figure 24). These three bands 

 are united to, and act in conjunction with, the great fibro elastic web c, to flex the fore- 

 arm on the arm. 



f g, h, i, Musculo-fibro-elastic ligament, which envelopes the roots of the primary and secondary feathers. 

 The musculo-fibro-elastic ligament forms a symmetrical network of great strength and 

 beauty, its component parts being arranged in such a manner as to envelope the root of 

 each individual feather. The network in question supports the feathers, and limits their 

 peculiar valvular action. It is enlarged at figures 25 and 27, and consists of three longi- 

 tudinal bands, r s, tu, viv. Between these bands two oblique bands, g and h, run; the 

 oblique bands occurring between every two feathers. The marginal longitudinal band 

 (v, iv) splits up into two processes, one of which curves round the root of each feather (x) 

 in a direction from right to left (a, b, c), the other in a direction from left to right (d, e,f). 

 These processes are also seen at in, n of figure 26. They have the root of each feather 

 completely under control, and their function, in conjunction with the oblique bands, is to 

 rotate the feathers from right to left during flexion, and from left to right during exten- 

 sion. The longitudinal and oblique bands are so geared together that they work in har- 

 mony, all the feathers enveloped by them being made to rotate in the same direction at 

 exactly the same instant of time. It is in virtue of the rotation of the individual primary 

 and secondary feathers at their roots that the feathers are separated from each other during 

 flexion, and brought into close contact during extension ; and thus it is that the air is 

 avoided during the up stroke, and seized during the down one. The primary and 

 secondary feathers are supported on their dorsal aspects by a series of subsidiary featheis 

 (inn op of figure 28), which are placed obliquely across their roots, and act as buffers. 

 The subsidiary feathers prevent the primary and secondary feathers from rising too far 

 during the down stroke. 



Figures 25, 26, and 27. See under figures 24 and 28. 



CONTENTS. 

 NATURAL FLIGHT. 



PAGE 



Introductory Remarks, . . . . . . . . . 32 1 



History of the figure of 8 theory ox Wing movements, ..... 322 



The Wing a twisted lever or helix, ........ 322 



The Wing twists and untwists during its action, ...... 325, 336 



The image produced on the eye by the Wing in motion is concavo-convex and twisted, . 336 



The Wing rotates on its long axis, ........ 336 



Compound rotation of the Wing, ........ 335, 375 



The Wing during its action reverses its planes, and describes a figure of 8 track in space, . 326 



