156 LECTURE V. 



The skeleton or bony frame of the animal is 

 in general of a lighter nature than in quadrupeds, 

 and is calculated for the power of flight : the spine 

 is immoveable, but the neck lengthened and flex- 

 ible : the breast-bone very large, with a prominent 

 keel down the middle, and formed for the attach- 

 ment of very strong muscles: the bones of the 

 wings are analogous to those of the fore-legs in 

 quadrupeds, but the termination is in three joints 

 or fingers only, of which the exterior one is very 

 short. What are commonly called the legs are 

 analogous to the hind-legs in quadrupeds, and they 

 terminate, in general, in four toes, three ^f which 

 are commonly directed forwards, and one back- 

 wards ; but in some birds there are only two toes, 

 in some only three. All the bones in birds are 

 much lighter or with a larger cavity than in 

 Quadrupeds. 



With respect to the definition of a Bird, as ab- 

 solutely distinguished from all other animals, it 

 would be sufficient to say, according to the old 

 mode, that a bird is a two-footed, feathered animal. 

 The power of flight need not enter into the defini- 

 tion i for there are many birds which are perfectly 

 destitute of the power of flight j as the Ostrich, 



