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 something 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 feel- 

 ing that the head contains a hard skull ; the lower jaw, a 

 lower- jaw-bone or mandible ; that running through the 

 back is a jointed backbone or vertebral column; that 

 the region of the chest is protected by a breastbone or 

 sternum ; and that each division of the limbs has its own 

 bone or bones. 



The Mouth-Cavity. There are also several points to 



