222 



A COURSE ON ZOOLOGY. 



Rodents have the upper lip slit vertically, giving a pe- 

 culiar physiognomy; this condition occurs sometimes in 

 man as a defect, and is called harelip. Generally, rodents 

 are herbivorous or frugivorous ; some, however, such as 

 rats, are omnivorous. Most of them are small ; the 

 limbs are organized for jumping rather than walking, 

 the hind quarters being higher than the shoulder. The 

 brain is not highly developed. They are timid, and only 

 moderately intelligent, although endowed with remark- 

 able instincts. Nearly all are nocturnal, digging gal- 

 leries, and passing three-fourths of their existence under- 

 ground ; some are semi-aquatic, and a few live in trees. 

 In general they have an instinct of foresight, and lay 

 up for winter a store of provisions, consisting of grains 

 and fruits, in quantity much greater than their real ne- 

 cessities require. Sev- 

 eral hibernate during 

 the cold season. 



Of all the orders of 

 mammals the rodents 

 are most widely dis- 

 tributed over the 

 earth's surface, repre- 

 sentatives being found 

 in every country on 

 the globe. There are 

 more than six hundred 

 species ; many of them 

 may be considered use- 



COMMON SQUIRREL (Sciurus vuigaris). ful to us, because we 



use their skins for furs 



and their flesh for food ; but the necessities of their diet 

 nearly always render them injurious to agriculture, es- 



FIG. 151. 



