OF THE UNITED STATES 423 



found haunting either the woods or the open cultivated fields. 

 Smaller by all odds than many of its kin in foreign lands, it is 

 when captured found to be a gentle and timid little creature, that, 

 with pains and care, is soon broken to domestication and makes 

 a very interesting little pet. 



All of our United States mice belong to the Family Muridce, a 

 group that likewise includes the Muskrats (Fiber, Ncofiberj ; the 

 Lemmings (Myodes) ; and the Cotton and Wood Eats (Higmo- 

 don, Neotoma). And, as has before been said, this family of the 

 Muridce belongs to the Order Rodentia, that includes, besides the 

 Squirrels (Sciuridw) and the Mice, the Jumping Mice (Zapodidcv) ; 

 the Porcupines (Hystricidce) ; the Pikas (Lagomyidw) ; and the 

 Hares (Leporidw). Representatives of all of these families are to 

 be found within the boundaries of the United States, while others 

 of the Rodentia occur not only in Mexico and Central America, 

 but the world's fauna at large oft'ers as many more, and very re- 

 markable rodentine families, containing many species and sub- 

 species. Comparatively speaking, the order Rodentia is composed 

 of mammals of small size, the largest form known to it being 

 the famous Capybara (Hydrochoerus capybara) of South Amer- 

 ica, while some of the little pocket-mice represent, next to some 

 shrews, the smallest of all known mammals. Rodents are mostly 

 terrestrial forms rarely given to tree or aquatic life, and there are 

 probably a thousand good species of them known to science, with 

 a great many more yet to be discovered and described. Animals 

 of this group have no canine teeth, and are readily known by their 

 stout, chisel-shaped incisors, of which, with the exception of Lago- 

 morpha, there are commonly two in each jaw, just as we find them 

 in a squirrel. There are never more than two incisor teeth in 

 the lower jaw in any rodent. These incisor teeth are very re- 

 markable, growing as they do from persistent pulps, and without 

 interruption. Their roots are long and curved, extending far 

 back into the skull or the mandible, the aforesaid pulp from 

 which they continually grow being at the hinder extremities, 

 while their anterior, chisled ends are kept permanently sharp by 

 the friction between the free edges of the upper and lower pair. 

 From one cause or another it sometimes happens, as in the case of 

 a rabbit or squirrel, that the opposing surfaces or edges are dis- 

 torted, whereupon the misplaced tooth or teeth having no op- 

 posed one to wear it off, continues to grow on without interrup- 

 tion, and as the form of the tooth is curved, it usually grows back- 



