452 THE MECHANICAL FUNCTIONS. 



suppose the lengthened body of a serpent to be 

 capable, it will, at first view, be difficult to con- 

 ceive how these simple actions can be rendered 

 subservient to the purposes of progression on land : 

 and yet experience teaches us that few animals 

 advance with more celerity on the surface of the 

 ground, or dart upon their prey with greater 

 promptitude and precision. They raise them- 

 selves without difficulty to the tops of the highest 

 trees, and escape to their hiding places with a 

 quickness which eludes observation and baffles 

 the efforts of their pursuers. 



The solution of this enigma is to be sought for 

 partly in the structure of the skin, which, in 

 almost every species, is covered with numerous 

 scales : and partly in the peculiar conformation 

 of the ribs. The edges of the scales form rough 

 projections, which are directed backwards, so as 

 to catch the surfaces of the bodies to which they 

 are applied, and to prevent any retrograde mo- 

 tion. In some species, the integument is formed 

 into annular plates, reminding us of the struc- 

 tures so prevalent among worms and myriapode 

 animals. Each scale is connected with a parti- 

 cular set of muscular fibres, capable of raising 

 or depressing it, so that in this way it is con- 

 verted into a kind of toe ; and thus the body 

 rests upon the ground by numerous fixed points 

 of support. 



This support is further strengthened by the 



