82 THE FLIGHT OF BIRDS 



radius) is pulled towards the body when the elbow 

 is straightened and this straightens the wrist. A 

 further result inevitably accompanies the first 

 straightening movement. There is an elastic liga- 

 ment that stretches from the armpit to the extremity 

 of the digits. Through this pass all the secondary 

 flight-feathers and, in every bird in which I have 

 traced its course, all the primaries (those that spring 

 from the hand). Part of this ligament is shown in 



Fig. 24. 

 Wing viewed from below (after Alix, with a slight alteration, 

 see text). AM : Muscle and tendon supporting anterior mem- 

 brane, Dl : Digit 1. El: Elastic ligament. F: Flexor carpi 

 ulnaris, dividing into two. T : Tendons connecting muscle with 



quills. 



figure 24. But it is easy to see the whole of it in 

 any bird's wing when the small covering feathers 

 have been removed. The straightening of the wing 

 stretches the ligament and the great flight-feathers 

 spread like a fan.* {See PL xi.) 



* There are differences in different families. In some the liga- 

 ment, instead of being pierced by the quills, fastens only to their 

 under-side. 



