CHAPTEE XV 



UODENTIA TILLODONTIA 



Order IX. RODENTIA' 



Small to moderately large animals, furry, sometimes with spines. 

 Toes with nails of a claw-like character, or sometimes approach- 

 ing hoofs. Usually plantigrade, and only occasionally and 

 partly carnivorous. Canine teeth absent ; incisors long and 

 strong, growing from persistent pulps, and with enamel only or 

 chiefly on the anterior face, producing a chisel-shaped edge; 

 molars few (two to six), separated from the incisors by a wide 

 diastema. Caecum (nearly always present) very large, and often 

 complicated in structure. Brain, if not smooth, with few furrows, 

 the hemispheres not overlapping the cerebellum. Surface of skull 

 rather flat ; orbits not separated from temporal fossae ; malar 

 bone in middle of zygomatic arch ; palate very narrow, with 

 elongated incisive foramina ; articular surface for lower jaw 

 antero-posteriorly elongated. Clavicles generally present. Testes 

 generally abdominal. Placenta deciduate, and discoidal in form. 

 The Rodents are a very large assemblage of usually small, 

 sometimes quite minute, creatures, embracing an enormous 

 number of living generic types. They are distributed all over 

 the world, including the Australian region, and, being small and 

 often nocturnal, and by no means particular in their diet, have 

 managed to thrive and multiply to a greater extent than any 

 other group of living mammals. They are chiefly terrestrial 

 creatures, and often burrow or live in ready-made burrows. 



' See especially Tullberg, " Ueber das System der Nagethiere, " Act. Ak. Upsala, 

 1899 ; and Alston, Pi-oe. Zool. Soc. 1875, p. 61 ; and for nomenclature, Thomas, Proc. 

 Zool. Soc. 1896, p. 1012 ; and Palmer, Prnc. Biol. Soc. Jt'ds/nngfMi, xi. 1897, p. 241. 



