THE LIVING WORLD 221 



the brain, and ramify in the membrane which lines the 

 back of the nostrils. Similarly the tongue and hinder 

 part of the palate are supplied with tasting or gustatory 

 nerves which also proceed from the brain, though from 

 quite its hinder portion . 



The spinal cord gives off nerves on either side 

 symmetrically in pairs, each nerve arising by two 

 roots, one from the front and one from the back of 

 the cord.* 



The cat's body possesses what is called bilateral sym- 

 metry, that is to say there is a close resemblance and 

 correspondence between its right and left sides, though 

 this does not apply to all its internal organs. There is 

 also a serial symmetry as, e.g., between the front and 

 the hind leg, between the successive ribs of either 

 side, and between the successive bones which together 

 make up the back-bone. 



Such being the structure of the cat, we have next to 

 consider its physiology the functions of its various parts. 



We have seen that protoplasm has a power of con- 

 traction. This exists greatly intensified in muscular 

 tissue, and all the cat's movements are performed 

 through contractions of its muscles which move the 

 bones to which they are attached, causing them to act 

 like levers of different orders.f Thus, when the cat 

 raises its fore-paw to strike, the paw is the weight, the 

 fulcrum is the lower end of the bone of the upper part 

 of the fore-leg, and the force or motive power is the 

 muscle which is attached to a bone of the lower part of 

 the fore-leg, and which, by its contraction, raises the 

 paw, and so this action is an example of a lever of the 

 third order. 



* See Fig. 44, p. 226. f See ante, p. 51. 



