CHAPTER XXXI 



BIRDS, THEIR STRUCTURE AND ADAPTATIONS 



Vocabulary 

 Flexible, easily bent. 

 Impair, to interfere with. 

 Competent, able. 

 Concave, curved in. 



Eliminate, to excrete or throw off, as waste. 

 Coordinate, to make to work together. 

 Acute, keen. 



The group of birds is one of the most familiar, useful, and 

 interesting, of all the animal kingdom. Among the vertebrates 

 they are the most highly specialized in structure, every organ 

 being adapted for the one object, namely, flight. 



Birds are sharply distinguished from all other animals by the 

 following points, among many others: 



1. Their body is covered with feathers. 



2. Their forelimbs (arms) are developed as wings, solely for 

 locomotion and never for prehension. 



3. The mouth is provided with a horny, toothless beak. 



4. The body is supported on two limbs only (like man). 



Adaptations for Flight. The general smooth outline, due to the 

 thick covering of feathers, permits easy and swift passage through 

 the air with little resistance. The flexible neck and legs provide 

 for easy " fore and aft " balance, while the wings, being attached 

 high above the bulk of the body, prevent danger from tipping 

 over sidewise. Lightness is secured by very slender, hollow, air- 

 filled bones, with few heavy joints; by numerous air sacs scattered 

 through the body; by feathers for covering and locomotion; and 



281 



