62 CALIFORNIA MAMMALS. 



Order Glires. (The Rcxlents or Gnawers.) 

 Incisors two in lower jaw^ usually two but occasionally four 

 in upper, larg-e, with chisel-shaped points, fitted for gnawing; no 

 canines, but a considerable gap in their usual place; premolars 

 present in some families, absent in others; molars tisually three in 

 each side of each jaw, adapted for grinding-; condyles of lower 

 jaw not received in special sockets, but permitting more or less 

 longitudinal grinding- movement of the jaw; cerebrum small, 

 but little convoluted; clavicles present but sometimes rudiment- 

 ary; digits generally five, furnished with nails or claws; food 

 chiefly vegetable; modes of life greatly diversified. 



Rodents form the largest order of mammals, coniaming- near- 

 ly or quite one thousand living species. It is also the most widelv 

 distributed terrestrial order. South America seems to be the 

 center of distribution. 



Suborder Simplicidentata. 



But one pair of upper incisors; enamel coating incisors con- 

 fined to their front surfaces; incisive foramina distnici and or 

 moderate size. 



The general structure of the various genera of this sul3- 

 order are so similar that the characters available for distinguish- 

 ing them are comparatively trivial and of slighr structural im- 

 portance. 



Family Sciuridae. (Squirrels.) 

 Skull varying with genera in length relative to breadth ; post- 

 orbital processes present, Aarious in form; first premolar small, 

 often deciduous; molars rooted, tubercular; palate broad; clavicles 

 developed; fibula free; tail without scales, well haired, various in 

 length of vertebrc-e and hairs; ears varying in length from quite 

 long to rudimentary. 



The Squirrels are a large and important family of rather 

 small sized mammals. They are distributed over nearly all parts 



