AEEIAL LOCOMOTION 



229 



record the contractions of the pectoral muscles. A 

 long flexible tube unites the capsule and the chamber 

 of a recording tambour. This tube does not impede 

 the bird's flight, but allows a record to be obtained 

 which shows variations according to the species of bird 

 used in the experiment. By means of a tuning-fork 

 and chronograph, the duration of the different phases 

 of muscular action occurring 

 during the movements of the 

 wings can be estimated 

 r J-Q of a second. 



We will not dwell upon the 

 interpretation of these curves, 

 since the variations depend 

 largely on questions of com- 

 parative anatomy. 



Record of the Trajectory of 

 a Bird's Humerus. — To fully 

 understand the mechanism of 

 the wing movement, we set 

 up some rather complicated 

 apparatus so as to register 

 the trajectory of the humerus 

 of the bird with the variations 

 in inclination of the surface 



of the wing at different periods of the movement. In 

 different species we found the form of the curves 

 slightly different, but they all took more or less the 

 shape of an ellipse, the principal axis of which was 

 directed downwards and forwards. These experiments 

 were very difficult to carry out ; we succeeded, never- 

 theless, in repeating them a number of times with 

 practically the same result, and the buzzard which we 

 used in the experiments in the end became quite tame 

 and accustomed to the apparatus. 



The trajectory of the humerus of the buzzard proved 



Fig. 159. — Myographic record of the 

 pectoral muscles of a bird in flight. 



