xii INTRODUCTION. 



With the exception of variations in the shape and 

 length of the bill, neck and limbs, the shape of birds is 

 very constant. The neck is always long compared with 

 that of other animals, and very flexible, to make up 

 for the inflexibility of the body, which is always com- 

 paratively short. 



The true tail is movable only at the root and is always 

 short, although the feathers on it may be of great 

 length. 



The fore-limbs or wings are modified for the support 

 of the quill feathers ; the bones of the hand being fused 

 together and encased in a common skin, with the excep- 

 tion of the thumb, which carries a little plume of stiff 

 feathers. The arm is folded up in a " Z " shape, with 

 the hand or " pinion " pointing backwards. 



The wings of flightless birds often show some depar- 

 ture from this type, but they are always obviously 

 degenerate wings, pointing to the fact that their 

 possessors have degenerated from flying birds, and do 

 not bear any resemblance to the paws of reptiles. In 

 many birds claws are present on the first finger, and in 

 some cases on the second also. 



On the hand or pinion grow the primary quills, which 

 are the chief agents in flight. If they are clipped in 

 both wings the bird cannot fly by reason of the reduc- 

 tion of the wing area, nor can it, if only one wing 

 be operated upon, by reason of the destruction of the 

 balance. 



The secondary quills, which grow on the fore-arm, 

 and largely or entirely cover the primaries in repose, 

 can be clipped without destroying the power of flight. 



The innermost secondaries are often different in form 

 and colour from the rest, and are hence called tertiaries. 



The remaining small feathers of the wing are known 

 as coverts. 



In flying birds the front edge of the wing nearest the 

 body is formed by a membrane or web, which stretches 



