CHAPTER II 



THE FROG {continued) : general internal structure 



You have now seen that a frog can perform a number of 

 very complicated actions ; and, if you have any curiosity 

 in these matters, you will probably want to know some- 

 thing of the mechanism by which these actions are 

 brought about. Now, the best way to understand the 

 construction of a machine, such as a clock or a steam- 

 engine, is to begin by taking it to pieces ; and, in the 

 same way, you can find out the parts of which the 

 living machine we call a frog is made, and the way they 

 are related to one another, only by taking it to pieces, or 

 dissecting it. 



First notice, in addition to the external characters described 

 in the last chapter, that the various parts of the body 

 are strengthened or stiffened, as in ourselves, by a number of 

 bones, which together form the greater part of the skeleton. 

 It is quite easy to ascertain by feeling that the head con- 

 tains a hard skull; the lower jaw, a lower-jaw-bone or 

 mandible ; that running through the back is a jointed 

 vertebral column, or back-bone ; that the region of the 

 chest is protected by a sternum, or breast-bone , and that 

 each division of the limbs has its own bone or bones. 



The Mouth-Cavity. — ^There are also several points to 



