CHAPTER II 



THE FROc; {continued) : general internal structure 



\'ou have now seen that a frog can perform a number of 

 very com[)Hcated 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 bust 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 tind 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 

 6(7nes, 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 



