296 



ANIMAL MOVEMENT 



chuting fold of a Bat, and the latter to that part of the "wing" 

 of that animal which occupies the region of the arm-pit. As we 

 shall see later, these folds have a purpose to serve in flight. 



The direct evidence so far at our disposal as to the evolution 

 of Birds' wings is unfortunately exceedingly scanty. For in the 

 oldest known extinct member of this class (Archczopteryx, fig. 

 831) the fore-limb was a well-developed wing, though somewhat 



less specialized than in living 

 forms. For example, claws were 

 present on all three digits. Al- 

 though an undoubted bird, with 

 wings and feathers, this ancient 

 type approximated to reptiles in 

 several respects, notably in the 

 presence of well-developed teeth 

 and a long tail. There are good 

 reasons for thinking that Birds 

 are descended from reptilian an- 

 cestors, though none of the known 

 groups of Reptiles can be worked 

 into their pedigree. But it is 

 permissible to picture those an- 

 cestors as hopping forms (see 

 p. 185), which first took to climb- 

 ing and then to parachuting. 

 And it is quite conceivable that 

 the two wing - membranes of a 

 Bird are the last remains of para- 

 chuting arrangements, of which 

 the hinder one has long since been superseded by feathers, the 

 evolution of which was associated with the development of flying 

 powers. This view, however, must only be regarded as a specu- 

 lation. 



Feathers. The possession of feathers is so eminently charac- 

 teristic of Birds, that to define these as " Feathered Animals J> 

 would suffice to mark them off from all other creatures, living 

 or extinct, of which we have at present any knowledge. As 

 regards flight, the most important of these structures are the 

 " quills " attached to wing and tail. The former are known as 

 "rowing feathers" (remiges) and the latter as "steering feathers '" 





Figr. 831. Extinct Toothed Bird (Archceopteryx) 



j\ Toothed jaws; cl, collar-bone; , ulna; 2 and 3, 

 second and third fingers ; s, shin-bone ; sh, shank- 

 bone; in, third toe; t, axis of tail. 



