x.] RODENTIA. 179 



moderately developed paroccipital processes, which in the 

 Capybara (Hydrocharus) are of great length, curving for- 

 wards and compressed laterally. They are also very large 

 in the Coypu (Myopotamus). 



The parietals are moderate or small. The frontals, except 

 in the Squirrels, Marmots, and Hares, have little more than 

 a rudiment of a postorbital process, and there is never any 

 marked corresponding process arising from the zygoma, so 

 that the orbit is perfectly continuous with the temporal fossa. 

 The latter is always very small. 



In a very remarkable East African genus, Lop/iiowys, a 

 broad bony lamella extends from the upper part of the 

 parietal outwards and downwards to join a similar ascending 

 plate from the malar, and thus forms an arched covering 

 to the temporal fossa, an arrangement unknown in any 

 other Mammal, but recalling that met with in the Tortoises. 

 The whole of the superior surface of the cranial bones of 

 this animal are covered with miliary granulations, disposed 

 with perfect regularity and symmetry. 1 



The nasals in Rodents are both long and wide, and 

 generally extend so far forwards as to make the anterior 

 nares quite terminal and vertical, or even with a downward 

 inclination. In Hystrix their development is enormous, but 

 this is chiefly owing to their breadth and backward extension 

 over the great nasal chambers and air sinuses. They are 

 narrowest in Jiathyergus and its allies. 



The premaxillai are large, and lodge the great curved 

 incisor teeth,'- and always send a narrow prolongation back- 

 wards by the side of the rasals to join the frontals. 



1 See A. Milne-Edwards, Xour. Archiv. du Museum, iii. 1867. 



2 These teeth, though first developed in the gum covering the pre- 

 maxilla, have their roots, when fully developed, in the maxilla. This 

 does not invalidate their determination as incisors. 



N 2 



