MAMMALIA 



The price of seal-skins has varied with the year and the character 

 of the skins, ranging from about $8 to $40 each. 



The treatment of the seal-skin before it is ready to be made into 

 garments is rather an extended process and, of course, adds to the cost 

 of the finished article. 



Rodentia (Glires). Gnawing Animals. This is a large group of 

 small animals, whose chief characteristic is the possession of sharp, 

 chisel-like incisor teeth, which are particularly well adapted to gnawing. 

 There are never more than two incisors in the lower jaw and usually 

 only two in the upper jaw. The incisors and sometimes the back teeth 

 have persistent pulps which causes them to continue to grow, to make 



PIG. 145. Photograph of skull of woodchuck, showing an upper incisor that 

 had grown in an arc of a circle until it entered the roof of the mouth, after its oppos- 

 ing lower incisor had been broken off. X i . 



up for the wearing away of their cutting surfaces. If an incisor be 

 broken off, the opposite tooth, having no mate to wear against : will 

 continue to grow, in the arc of a circle, until it may cause the death 

 of its possessor, Fig. 145. No canine teeth are present, which leaves 

 a wide space between the incisors and the premolars. While rodents, 

 as a class, are vegetable feeders, some forms, such as the common rats 

 and mice, are practically omnivorous. The integument is usually furry, 

 sometimes hairy and occasionally spiny (Porcupines); the digits end 

 in claws; the cecum is very large; the cerebral hemispheres are com- 

 paratively smooth. 



This extensive order of more than 1400 species includes the 

 following well-known North American families: Muridae, the rats 



