FLIGHT 



203 



feathers themselves greatly reduces 

 the work of the muscles and tendons 

 in making the adjustments that arc 

 required in order to render the wing 

 impervious to air (fig. 55). 



The Active Machinery. 



The great muscles of flight lie below 

 the shoulder joint, and yet upon them 

 falls the task of raising the wing. All 

 the great mass of muscle lies behind 

 the joint, and yet the wing must be 

 lowered without being pulled back- 

 ward. Besides this the muscles can 

 incline the wing rightly for upward 

 flight, for a downward swoop, for a 

 sudden halt ; they can adjust it to 

 every varying breeze, to every current 

 or eddy that can be turned to account. 

 In addition to the breast muscles, 

 there are many smaller ones which 

 help in these niceties of adjustment. 

 When we consider the number of 

 these, each with its special office, each 

 giving the wing a slightly different 

 turn from any other, it is extraordinary 

 that Professor Marey should state that 

 " the muscular apparatus of the bird, 

 like that of the insect, has nothing FlG - 55— Primary 



„ & wing feather of Heron 



to do with the course of the wing ; fis? 8 than natura ! size ) 



53 ' T. he outer web is nar- 



devation and depression are almost the row - 



