I s<; 



BRANCH VERTEBRATA. 



FIG. 318. 



ORDER RODENTIA (ro den'shi a). 



The Rodents (gnawers) lack canine teeth, but have 

 two upper and lower incisors, fitted to gnaw bark, roots, 

 woody stems, nuts, etc. These are long, slightly curved, 



and deeply rooted in the jaw. The 

 molars are generally ridged trans- 

 versely, and the lower jaw moves 

 backward and forward in mastica- 

 tion. Most of the order have clav- 

 icles, and hence rotary motion of 

 the arms, allowing the food to be 

 held to the mouth while gnawing. 

 The edges of the teeth are of necessity always sharp, 

 since the anterior portions are protected by an intensely 

 hard and resisting enamel, while the softer substance of 

 the back is constantly being worn away.* 



n i f Tail short, i 



I MOLAR TEETH I furpy \ Hare. 



rudimentary. \ WITHOUT BOOTS. 



1 Tailless ............ Guinea Pig. 



( Tail short. \ , 



\ Porcu)nne. 

 bristly. > 



Skull of a Rodent. 



RODENTIA. ^ 



Clavicles 



f MOLAR TEETH 

 . well developed, f WITH ROOTS. 



Tail long, , Jumping 



thinly haired, i 



Gopher. 



Tail medium, ; 

 partially naked, f 



Tail varying in i , 



- Mouse. 

 length, scaly. ) 



Tail flattened, 

 scaly. 



I Beaver. 



Tail long, . 8quirrd 



bushy. ' 



fairly exhausted, we gave up, beaten. Such was the wonderful power in the tail 

 of that small animal." Two Tears in the Jungle. CHARLES SCRIBNER'S SONS, 1886. 



* If one of the incisors be broken off, its opposite continues to grow, some- 

 times curving, in which case at length it locks the jaw, and f he wretched animal 

 starves to death. 



