368 



BONES OF THE WING. 



named wings. When speaking of Bats, we saw an example of 

 the transformation of the thoracic members into an organ of 

 locomotion in the air ; in those animals it is a fold of skin which 

 serves to strike the air, and the fingers are much prolonged for 

 its support ; but in Birds these expansions are of a different 

 nature ; they are formed of stiff feathers, which require to be 

 fixed only at the base ; and the hand, consequently, no longer pre- 

 sents the division into fingers, 

 which would impair its solidity 

 without being of any use ; it 

 has the form of a flattened, and 

 almost motionless stump. The 

 conformation of the arm and 

 fore-arm differs little from that 

 of the same parts in Man ; 

 the humerus has no peculiarity; 

 the radius and ulna cannot 

 turn on one another, and are 

 generally longer as the flight 

 is more powerful. The carpus 

 is composed of two small bones 

 placed together, and followed 

 by the metacarpus, which is 

 formed of two bones united 

 at their extremities ; on the 

 radial side of the base of this 

 last part, is inserted a rudi- 

 mentary thumb ; and lastly, 

 at its extremity is a middle 



joint ; a, humerus ; b, radius ; c, metacarpus ; finger composed of two 

 o, rudimentary thumb ; 1, 2, 3, 4, rudiment- 



ary phalanges of fingers. langes, and a small D lament 



representing the outer finger. 



331. The wing feathers are distinguished as primaries, 

 secondaries, or tertiaries, according as they are supported by the 

 hand, the fore-arm, or the humerus ; and it is on their length, 

 more than on that of the wing bones, that the extent of the 

 wings and the power of flight depend. Whenever the Bird 



