BIRDS 199 



Ci lk \ II. -Aves (Birds). 



General Characters of Birds. — The graceful, pi 

 - of the bird's body; othing of feathers; the 



toothless jaws encased with horn to form the bill, and the 

 remarkable change "f the fore-limbs into wings — these are 

 i he marks which separate the birds from othi 



de8 this, they are warm-blooded, and (heir bones are 

 compacl and in manj cases hollow, thus combining 1 ■_ 



with strength; hence birds are the most active and 

 volatile creature- among all the back-boned annuals. The 

 vertebral column is so adapted that birds can fly in any di- 

 rection, particularly in a vertical one; and it is the strei 



a 



IT 6 



til. Various curves of the wing of a bird at different points in its 1< 



r Ma ivy. 



and flexibility of its spinal column that enables the lark to 

 rise up and shoot high into the air. Birds can turn the 

 head 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 i i 

 pari of its body with its bill. 



The most striking difference from other animals is in the 

 modification of the fore-leg into a limb which supports a 

 broad expanse of feathers, and ends in two rudimentary 

 boe-bones. Another peculiarity in the skeleton conn* 

 with the power of flight is the very large breast bone, with 

 its keel, which is very high and thin, serving for the at- 

 tachment of the muscles of B Thus in all respects we 

 see a complete adaptation of the bird's ly to its life in 

 the air. The wings are attached exactly at the hig 



