^be 1Ro6ent6 or (3nawinG Hnimale. 



SEVENTH ORDER: Rodentia. 



OH E order of the Rodents or 

 Gnawing Animals presents 

 a class of animals with 

 clearly defined limits. The 

 creatures belonging to it 

 are perhaps still more en- 

 titled to their name than 

 the beasts of prey 'are to 

 theirs. The distinctive 

 feature, common to all, is 

 found in the fact that two 

 incisors in each jaw are de- 

 veloped into large gnaw- 

 ing teeth, while the canine 

 teeth are lacking. Little can be said about the gen- 

 eral appearance of Rodents, as the order is rich in 

 families and species and comprises the most varied 

 forms. The following general characteristics may 

 be said to be found in them. The body, in the major- 

 ity of cases, is cylindrical and is supported by short 

 legs, usually of .unequal length, the hind-legs gen- 

 erally being somewhat the longer, and frequently 

 very much longer, than the fore-legs. The head is 

 set on a short, thick neck; the eyes are large and 

 usually very prominent, and the upper lip, which is 

 adorned with whiskers, is fleshy, very mobile and 

 cleft in front. The front feet, as a rule, have four 

 toes, the hind feet five, the toes being armed with 

 more or less strong claws and occasionally webbed. 

 The fur is nearly always of uniform length, except 

 that it sometimes shows tuft-like elongations at the 

 tips of the ears or becomes bushy at the tail. 



Diatinctiue The gnawing teeth (incisors) are 

 Gnawing Teeth considerably larger than any of the 

 of Rodents. others, the upper ones being always 

 the lower ones. Both upper and 

 are curved, the cutting edge being 

 broad or chisel-shaped; the base is either three or 

 four sided, and they may be flat or arched, smooth 

 or furrowed, of white, yellowish or red color. The 

 external or front surface of these teeth is covered 

 with enamel, which has the hardness of steel, and 

 forms the sharp point or the broad, chisel-shaped 

 cutting edge. The rest of the tooth consists of the 

 usual tooth pulp. Being subjected to continuous 

 use, these principal teeth would become blunt ' and 

 worn out in a short time, if they were not possessed 

 of a great advantage over the teeth of all other 

 mammals: their growth is unlimited. The root of a 

 tooth lies in a socket, which pierces deeply into the 

 jaw, and at the open extremity, in a funnel-shaped 

 cavity, the tooth contains a permanent germ, which 

 constantly supplies the tooth with a new growth as 

 it wears off in front. The trenchant sharpness of 

 the edge is preserved by the reciprocal friction of 

 the upper and lower teeth and the grinding effected 

 by it; the jaws have no lateral motion, and the lower 

 jaw can work only vertically or with a slightly pro- 

 jectile or retractile motion' from front to rear. In 



stronger than 

 lower incisors 



this way these teeth meet all the requirements of the 

 enormous expenditure of material the gnawing proc- 

 ess entails. It is easy to demonstrate the constant 

 growth of the gnawing teeth by forcibly breaking 

 one of them in some Rodent, for instance a Rabbit. 

 Then the tooth opposite the broken one, as it is no 

 longer worn off by friction, grows rapidly until it 

 stands out of the mouth in a narrow arch, and curves 

 inward like a horn, thereby mutilating all the other 

 teeth and rendering the sustenance of the animal 

 extremely difficult. With many of the Rodents 

 cheek-pouches open on the inner side of the jaws; 

 they may extend to the shoulders and serve to store 

 away the food as it is gathered. A special muscle 

 pulls these pouches back when they are about to be 

 filled. 

 Rodents Spread The Rodents are distributed over all 

 allouerthe continents and are found in all cli- 

 Earth. mates of any latitude and altitude, 



as far as there is any vegetation. "In the midst of 

 perennial ice and snow," says Blasius, "where a 

 warm ray of the sun shining but for a few weeks 

 calls forth a short-lived, scanty vegetation in places, 

 on the quiet, lonely, snowy heights of the Alps, in 

 the wide, desolate plains of the north, one still 

 finds Rodents, which do not yearn for a more beau- 

 tiful sun. The richer and more abundant the vege- 

 tation is, however, the more varied and manifold 

 grows the life of this order of animals, which scarcely 

 leaves a spot on earth uninhabited." 



Life and These widely distributed animals ex- 

 Habits of the hibit a great diversity in their ways 

 Rodents. and habits' Not a few of them lead 

 an arboreal life, many live on the ground; some live 

 in the water, others in underground burrows which 

 they dig for themselves; some in bushes, some in 

 the open field. All are more or less' active creatures, 

 and according to the character of their different 

 habitations and modes of life are either excellent 

 runners or climbers, diggers or swimmers. Most of 

 them are inquisitive and lively, but still they do not 

 impress one as sagacious or specially intelligent. 

 The great mass of them form a dull-witted mob, 

 which while timid, are neither cautious nor cunning, 

 and are never distinguished by any prominent intel- 

 lectual capacity. Some live in couples, some in 

 colonies, and not a few congregate in large com- 

 munities; they are on good terms with other ani- 

 mals, but do not associate much with them. Very 

 few exhibit a wicked, malicious, fierce or impudent 

 disposition, unless excited thereto by some extrane- 

 ous cause. At the approach of danger they retreat 

 to their places of concealment with all possible 

 speed; but only a very few species are intelligent 

 enough to baffle pursuit by craft. All Rodents feed 

 mainly on vegetable substances: roots, barks, leaves, 

 buds, fruit of all kinds, plants, grass, farinaceous 

 tubers and even wood fibres are consumed by them; 

 the majority, however, eat animal food also, and are 



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