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 iyArchcsopteryx, fig. 

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



ci less specialized than in living 



'^^§;;;v forms. For example, claws were 



^^^5\, present on all three digits. Al- 



^^^^^^^^(' ^ though an undoubted bird, with 



1^^ "'^!: y^~''~^^\\ , -S '^ wings and feathers, this ancient 



"^S?=~i^^iCD»^-cr.l^ type approximated to reptiles in 



^^^' y9^''\hK\ ^ M " several respects, notably in the 



/0Zf\^^^ZX\ '/£^ II presence of well-developed teeth 



;• t!>^^^^^^^ o^V.^^^\ and a long tail. There are good 



<''''"M'^=-^^ \ T reasons for thinking that Birds 



,r ' y/~^^ ^"/f'' — " ^^^ descended from reptilian an- 



&^X\^^^^ uf cestors, though none of the known 



:^%^M*f' \ ofroups of Reptiles can be worked 



^^3\y I A ^ into their pedigree. But it is 



C'^^y'\\ V rl---iii permissible to picture those an- 



''/^¥it\f~ " ' cestors as hopping forms (see 



'*/'/Ww P' ^^5)' '^^'^^ fi''^^ ^^^^ to climb- 



/^\ iji I ing and then to parachuting. 



" ^ "■ '' And it is quite conceivable that 



Fie. 831.— Extinct Toothed Bird (^r<;/2<r(7/i'i;>-jjr) . , ^ 



. ^ , , . , „ , , , the two winCT - membranes of a 



J, loothed jaws; ci, collar-bone; n, ulna; 2 and 3, "^ 



second and third fingers; s, shin-bone; s/t, shank- Bird arC the laSt rCmalnS of para- 



bone; ill, third toe; t, a-\is of tail. . _ ^ . ^ 



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 the hinder one has long since been superseded by feathers, the 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

 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" 



