: 8 ANIMAL LIFE PAST AND PRESENT. 



bird. Then, again, the larger and stronger feathers -of 

 the wings are the most efficient instruments for obtain- 

 ing the utmost advantage from the resistance of the 

 air to their strokes during flight. The peculiar nature 

 of the wings of Birds may be summarised by the state- 

 ment that whereas all other animals fly by means of 

 expansions of the skin itself, these alone fly by means 

 of separate outgrowths or processes developed from the 

 skin. 



The wing of a Bird, although constructed on the 

 same fundamental plan as that of a Pterodactyle, 

 differs altogether in the manner in which the bones 

 corresponding to those of the human hand have been 

 modified for the purposes of flight. In the wing of a 

 Bird only three fingers are represented at all, and 

 these probably correspond to the thumb, index, and 

 middle finger of the human hand. Moreover, while 

 the thumb is only represented by a small splint of 

 bone, carrying the so-called "bastard wing," the bones 

 of the index finger are flattened, and much larger than 

 those of the third one, with which, in living birds, they 

 are more or less closely un ted. This finger, therefore, 

 forms the chief part of the extremity of the wing or 

 pinion ; but, instead of its bones being much longer than 

 those of the arm and fore-arm put together, as is the 

 case with the elongated outer finger (4th or 5th, as the 

 case may be) of the Pterodactyle, it is much shorter ; 

 and, indeed, is frequently shorter than either the bone 

 of the upper arm or those of the fore-arm alone. The 

 finger, therefore, is the least important part of a Bird's 



