2 ANATOMY OF THE RAT 



to the front of the incisor, so that in gnawing the softer 

 dentine is worn away at the tip faster than the enamel, 

 thus keeping the tooth sharp. There are no canine teeth. 

 Rodents are mostly herbivorous in diet, are usually small, 

 and have clawed digits. The family Muridae, to which 

 rats and mice belong, is said to include nearly half the 

 genera of the Rodentia. 



Four common species of this family are found in the 

 United States. The common house mouse {Mus musculus) 

 is less than two hundred millimeters in length when adult. 

 The generic designation Epimys has been established for 

 the rats, but the older term Mus is doubtless more familiar. 

 Mus rattus rattus (the black, or house rat) is the rat 

 of the Middle Ages in Europe. It probably reached that 

 continent some six hundred years before the Norway rat 

 arrived. The black rat preceded the Norway rat in North 

 America, and occurs still in scattered localities in the 

 northern United States. Its diagnostic characteristics are: 

 the ears when laid forward extend at least to the middle 

 of the eye ; the tail is longer than the head and body ; and 

 is dusky all around ; hind foot 33-37 millimeters ; the color 

 is blue-black above, and slaty below. A color variety, Mus 

 rattus alexandrinus (roof, snake, or Alexandrian rat) is 

 "grayish-brown above, white or yellowish white below" 

 (Lantz). It is said to be common in the southern states 

 near the coast. Mus norvegicus (the brown, gray, barn, 

 wharf, sewer, or Norway rat) has, as a result of its adapta- 

 bility, fecundity, strength, and ferocity, largely replaced 

 the other species of rats in temperate climates. When well 

 fed it is said that a female Norway rat can give birth to 

 from sixty to a hundred young a year. It is more of a bur- 

 rower than the black or roof rat, and is the common form 

 found about bams, houses, warehouses, etc., in the United 

 States. This species' characteristics are: ''Ears moderate. 



