*eeth of Gnawing Mammals. 



107 



wears away more quickly than the harder enamel, the 

 tooth is kept constantly sharp ; hence when one 

 incisor in a rodent is broken, the one that should 



FIG. 51. 



Flying squirrel. 



oppose it grows on continuously, and sometimes this 

 mode of growth locks the jaws together. 



There are no canine teeth in rodents, and the 



