CLASS AVES. 



num, especially, to which are attached the muscles 

 which lower the wings in flight, is very much ex- 

 tended, and has its surface increased, moreover, by a 

 laminous projection in the middle. It is formed of 

 five pieces ; one central, of which the laminous pro- 

 jection makes a part ; two anterior lateral, for the 

 attachment of the ribs ; and two posterior lateral, for 

 the extension of its surface. The degree of ossifica- 

 tion of these last in each species denotes the pro- 

 portion of vigour for flight. 



The furca produced by the union of the two clavi- 

 cles^ and the two vigorous supports formed by the cora- 

 coi'd apophyses, widen the shoulders ; the wing, sus- 

 tained by the humerus, by the fore-arm, and by the hand » 

 which is long, and has one digit, and the vestiges of 

 two others, carries along its whole length a range of 

 elastic quills, which greatly extend the surface which 

 resists the air. The quills adhering to the hand are 

 called primari/, and there are always ten ; those be- 

 longing to the fore-arm are called secondary, and their 

 number varies ; feathers less strong, attached to the 

 humerus, are called scapular ; the bone which repre- 

 sents the thumb has also certain quills called bastards. 



The bony tail is very short, but it has also a range 

 of strong feathers, which, by spreading, continue to 

 support the bird : their number is commonly twelve, 

 but there are sometimes fourteen ; in the gallinaceous 

 birds there are eighteen. 



The feet have a femur, a tibia, and a peroneum 

 articulated to the femur by a spring, whose extension 

 is maintained without effort on the part of the muscles. 



