RODENTIA. 



Zeitschrift fur rationelle Medizin, Band v. 1846. 

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 von Athmen und vom Blutkreislauf, in Zeitschrift 

 fur rationelle Medizin, Band iii. 1845. Renter, Be- 

 leuchtung der Versuche von Prof. Scherer und Dr. 

 Bruch uber die Farbe des Blutes, in Zeitschrift fur 

 rationelle Medizin, Band iii. 1845. Letellier, In- 

 fluence des Temperatures extremes de 1' Atmosphere 

 sur la Production de 1'Acide Carbonique dans la Re- 

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 Rendus, torn. xx. 1845, and Annales de Chim. et 

 de Phys. torn. xiii. 1845. Mulder, Zur Frage, auf 

 welche Weise der Sauerstoff der Luft bei der Respi- 

 ration vom Blute aufgenommen wird, in Hollan- 

 dische Beitrage zu den anatomischen und physiolo- 

 gischen Wissenschaften, Band i. heft i. 1846. The 

 Chemistry of Vegetable and Animal Physiology, 

 translated from the Dutch by Dr. Fromberg, Edin- 

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 kohlensauren Alkalien im Blute, in Annalen der 

 Chemie und Pharmacie, Band Ivii. 1846. Animal 

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 zur Bestimmung des Wassergehalts der vom 

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(John Reid.) 



RODENTIA (Glires, Linn.) (Fr. Rongeurs). 

 An important order of mammiferous Verte- 

 brata, distinguishable by the remarkable struc- 

 ture of their incisor teeth, which are adapted to 

 perform the office of chisels by cutting and 

 gnawing away the hard vegetable substances, 

 which form their principal food. The animals 

 of this order, indeed, appear to be specially ap- 

 pointed to devour the hardest substances, ge- 

 nerally living upon the wood and bark of trees, 

 as well as upon nuts and other shelled fruits. 

 The incisor teeth, which characterize the ani- 

 mals of this order, are situated in both jaws, and 

 are separated from the molar by a considerable 

 space, so that they are ill-adapted to seize 

 living prey, or to devour flesh, notwithstanding 

 that certain genera of rodents exhibit decidedly 

 carnivorous propensities. These incisors, also 

 called denies scalprarii, are only provided 

 with enamel upon their anterior surface, 

 so that the posterior portion of the tooth 

 being worn away more rapidly than the an- 

 terior, these teeth always present a chisel-like 

 edge. The lower jaw is articulated to the 

 cranium by a longitudinal condyle, in such a 

 manner that it has no horizonal motion ex- 

 cept from before, backward, and vice versa; 

 a movement adapted to effect the act of 



gnawing. The molar teeth have their crowns 

 flattened and traversed by plates of enamel, 

 arranged transversely, the better to antagonise 

 the backward and forward movement of the 

 jaws. 



Fig. 247. 



Pteromys volitans. 



Those genera in which these layers of 

 enamel are simple plates, and which have the 

 crowns of their molar teeth very flat, are 

 more particularly frugivorous ; those in which 

 the eminences of these teeth are divided into 

 blunt tubercles, are omnivorous ; whilst a small 

 number of genera, which possess pointed mo- 

 lars, will attack other animals, and in some of 

 their habits approximate the Carnivora. 



This order comprises the following 

 genera : 



Sciurus (Squirrel). Pteromys (Flying 

 Squirrel) (fig. 247.). Cheiromys (Aye-Aye). 

 Arctomys (Marmot). Myoxus (Dormouse). 

 Echimys. Hydromys. Capromys. Mus(Rat). 

 Gerbilius. Meriones. Cricetus (Hamster). 

 Arvicola (Vole). Fiber (Musk Rat). Geo- 

 rychus (Lemming). Otomys. Dipus (Jer- 

 boa) (fig. 248.). Pcephagomys. Helamys. 

 Spalax (Rat Mole) (Jig. 249.) Bathiergus 

 (Cape Mole) (fig. 250.). Geomys. Diplo- 

 stoma. Castor (Beaver). Myopotamus(Coui). 

 Hystrix (Porcupine). Lepus (Hare). Lago- 

 mys (Rat Hare). Hydrochcerus (Capybara). 

 Rhyzomys. Cavia (Guinea Pig). Dasyprocta 

 (Agouti). Ccelogenys (Paca). Chinchilla. 



