62 CALIFORNIA MAMMALS, 



Order Glires. (The Rodents or Gnawers.) 

 Incisors two in lower jaw, usually two but occasionally four 

 in upper, large, 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 asually 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 greatl}- diversified. 



Rodents form the largest order of mammals, contaming" near- 

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

 distributed terrestrial order. South America seems to be the 

 center O'f distribution. 



Suborder Simplicidentata. 



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

 fined to their front surfaces; incisive foramina distmct and or 

 moderate size. 



The general structure of the ^•arious genera of this sub- 

 order are so similar that the characters available for distinguish- 

 ing them are comparatively trivial and of slight structural im- 

 portance. 



Family Sciuridse. (Squirrels.) 

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

 orbital processes present, various 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 vertebras 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 



