EODKNTIA, 163 



Ord. RODENTIA. 



Syn. Glires of some. 



Two incisors only in each jaw, large, incurved, and without roots. No 

 canines. Molars separated from the incisors by an interval, usually few in 

 number, varying from two to six on each side, rarely more than four. Feet 

 unguiculate, generally with five toes. 



The so called iacisors are, howeverj by most anatomists considered the 

 representative of canine teeth, the incisors being obliterated except in hares, 

 Vfhich have a pair of incisors behind the upper gnawing teeth.* 



The Eodents or Gnawers are chiefly characterized by the remarkable 

 conformation of their teeth. Their quasi-incisors have a plate of enamel 

 only in front, often colored yellow or brownish ; behind this the anterior 

 plate of true dentine is also harder than the posterior layer, though 

 not so hard as the enamel. From this structure a sharp edge is effected 

 by the constant attrition, the teeth acquiring a chisel-shape with the 

 slope backwards. The pulp being persistent, these teeth are always 

 growing, and if from any cause the upper tooth is displaced or lost, 

 its antagonist in the lower jaw has been known to grow on, enter the 

 skull, and cause death. The molars have flat crowns, and the ena- 

 melled eminences, which are always transverse, vary from thin lines 

 to blunt tubercles, according as their diet varies from frugivorous 

 to omnivorous. The condyle of the tower jaw is longitudinal, and slides 

 backwards and forwards, and this motion acting on the peculiar chisel- 

 shaped incisors, serves to reduce the hardest substances by a constant filing 

 or gnawing. The orbits are not separated from the temporal fossse. The 

 intermaxillaries are enormously developed to hold their large incisors, and 

 the maxillaries are therefore pushed far backwards. The nasal bones 

 are greatly elongated. Some possess clavicles, other have none. The os 

 magnum of the carpus is often divided into two, as in some monkeys. 

 The pelvis resembles that of Carnivora. The fibula is situated behind the 

 tibia, and consolidated with it in the lower portion in many. The os calcis 

 is much developed. » 



The stomach is usually simple or in two distinct pouches ; the intestinal 

 canal is very long, and pretty even in diameter ; and the coecum is general- 

 ly much developed ; and is only absent in one group. The liver is large, 



. • I shall continue to call these teeth the Incieors, or quaBi-inciaors. Blyth has lately named them 

 the rodential tusks. 



