58 THE STORY OF BIRD-LIFE. 



which we call — the fore- and hind-limbs of the 

 horse and dog, the arms and legs of the man, 

 the wings and legs of the bird or bat. The 

 wings then are homologous with our arms, and 

 the horse's fore-limbs ; they are developed from 

 the same parts in the unborn young or embryo. 

 The butterfly and the bee have six legs, which 

 cannot be compared 'with our legs, except in 

 so far as they perform the same function of sup- 

 porting the body. The wings certainly then 

 cannot correspond to our fore-limbs. Moreover, 

 there is some evidence tending to show that 

 the wing in these last is a highly specialised 

 and modified gill. 



The plan upoji which the bird's wing is built 

 is quite different. Let us compare it with our 

 own arm and hand. The wing of a bird then 

 and the " arm" of a man are precisely similar in 

 kind, but the former has become much more 

 highly specialised or modified, so as to perform 

 the office of a wing. To this end, as we shall 

 see, certain fingers have been lopped off, and the 

 remainder so altered as to be scarcely recognis- 

 able. The wing and the arm are both divisible 

 into three main divisions: (1) the long single 

 bone from the shoulder to the elbow called the 

 "arm"; (2) the two long bones from the elbow 

 to the wrist called the "fore-arm"; and (3) the 

 series of bones from the wrist to the fingers 

 which make up the hand ! It is in the form of 

 the wrist and hand that the bird differs from 

 ourselves. The bird has retained but three of 

 his original five fingers. One of these forms the 

 tiny thumb ; the second or index finger, and the 



