SERPENTS. 



155 



as the ribs move in pairs, the scutum under each 

 pair is carried along with it. This scutum, by its 

 posterior edge, lays hold of the ground and be- 

 comes a fixed point from whence to set out anew\ 

 This motion is beautifully seen when a snake is 

 climbing over an angle to get upon a flat surface. 

 When the animal is moving, it alters its shape, 

 from a circular or oval form to something ap- 

 proaching a triangle, of which the surface on the 



SKELETON OP BOA. 



ground forms the base. The Coluber and Boa 

 having large abdominal scuta, which may be con- 

 sidere'd as hoofs or shoes, are the best fitted for 



