CHAPTER XXX. 

 THE BIED8. 



Ant bird selected at random, so much alike are they all, 

 will serve as an example of the class. We will suppose the 

 student to have before him a dove; by studying this he can 

 readily grasp the characters which distinguish birds from 

 all other animals. 



The graceful, pleasing lines of the bird's body ; its cloth- 

 ing of feathers ; the toothless jaws encased with horn to 

 form the bill, and the remarkable change of the fore-limbs 

 into wings — these are the marks which separate the birds 

 from other vertebrates. Besides this, they are warm- 

 blooded, and their bones are compact, and in most cases 



Fig. 201.— Various curves of the -wing of a bird at different points in its lengtli. 



hollow, thus combining lightness with strength ; hence 

 birds are the most active and volatile creatures among all 

 the backboned animals. The vertebral column is so 

 adapted that birds can fly in any direction, particularly up- 

 wards ; and it is the strength and flexibility of its spinal 

 column that enable the lark to rise and shoot high into the 

 air. Birds can turn their heads around and look directly 

 back, as seen in the owls : this is owing to the unusually 

 free articulation of the first neck- vertebra to the skull ; 

 thus, the bird can reach every part of its body with its bill. 

 The most striking difference from other animals is in 



