XXll INTRODUCTION. 



these organs become more and more subordinate, they are 

 greatly assisted by the lateral motion of the bodies, different 

 parts of Avhich are brought into alternate contact with and 

 pressure upon either the roughness of the ground, or the 

 shrubs and herbage through wl^ich they pass. A comparison 

 of the progression of these, however, and even of the Slow- 

 worm, with that of the true Snakes, will show that the latter 

 only employ the free terminations of their ribs as organs of 

 locomotion. In these the ribs serve absolutely and perfectly 

 the function of feet, and with the exception of their being 

 covered with integument, their action is exactly that of the 

 multitudinous feet in the Scolopendra or Julus, the whole 

 series of ribs coming into contact in succession. At 

 the same time, it is upon the lateral motion of the body and 

 the alternate lateral pressure of successive portions of it, that 

 the Serpents mainly depend for the rapidity of their pro- 

 gression. 



It appears almost necessary to apologise for offering this 

 shetch of some of the most important phenomena in the 

 structure and habits of the different groups of existing Rep- 

 tilia. I have been induced to do so by the consideration that 

 very little is popularly known respecting them, and by the 

 eagerness with which information of this nature is sought by 

 many, w^hose habits and opportunities forbid any personal in- 

 vestigation into the depths of anatomical and physiological 

 science. 



