BIRDS. 



'3S5 



trary, the ribs, and the viscera which they protect, are 

 placed as far back along the spinal column as possible; and 

 a long and flexible neck extends from the trunk to the head, 

 which is thus carried considerably forwards. These circum- 

 stances are very apparent in the skeleton of the swan, re- 

 presented in Fig. 224. In the fish, progressive motion is 



eff'ected principally by the movements of the tail, which im- 

 pels the body alternately from side to side: in the bird, the 

 only instruments of motion are the wings, which are affixed 

 to the fore part of the trunk, and are moved by muscles situ- 

 ated in that region. In the fish, the spine is flexible ncar- 

 VoL. I. 49 



