FRET OF BIRDS. 587 



Ostrich has only two toes, one having four, and 

 the other five phalanges ; here, again, it is the 

 innermost of the three former, that is, the one 

 having three phalanges, which has been sup- 

 pressed.* 



A bird is capable of shifting the position of 

 the centre of gravity of its body, according as 

 circumstances require it, simply by advancing or 

 drawing back its head. While flying, the neck 

 is stretched forwards to the utmost, in order to 

 bring the centre of gravity immediately under 

 the origin of the wings, by which the body is 

 then suspended. When birds stand upon their 

 feet, they carry the head back as far as possible; 

 so as to balance the body on the base of support. 

 When preparing to sleep, they bring the centre 

 of gravity still lower, by turning the head round 

 and placing it under the wing. These motions 

 of the head are again resorted to when the bird 

 walks ; and the centre of gravity is thus trans- 

 ferred alternately from one foot to the other : 

 hence, in walking, the head of a bird is in con- 

 stant motion ; whilst the duck and other birds, 

 whose legs are very short, have a waddling 

 gait. It may be observed that the more per- 

 fectly predaceous birds are not the best formed 



* The last bone of the outer toe of the ostrich is very small, 

 and being usually lost in preparing the skeleton, has been over- 

 looked by naturalists ; but Dr. Grant has ascertained, by the 

 careful dissection of a recent specimen, the existence of this 

 fifth phalanx. 



