198 RODENTIA. 



coarse, and even quills, in others. Most have a great variety of powers 

 with their fore-teeth : they are a kind of carpenter's tools, becoming a 

 compound instrument. [See the concluding paragraph of this Section.] 



The first, then, or most striking characteristic of this order of animals 

 is the fore-teeth, having two above and two below, which are long, and 

 narrow at their ends, falling off from their external surface, where the 

 edge is, to the internal, like a chisel ; from the fore-teeth a vacuity is 

 continued to the grinders. 



Their lips are of a peculiar structure. Their tongue is thick between 

 the upper and under surface and narrow laterally ; adapted to the shape 

 of the mouth ' : it has a very little motion in it, never passing beyond 

 the teeth. 



The second characteristic is a flat head laterally, nearly of an equal 

 thickness at the nose and ears, curved on the fore-part like a bow from 

 the crown to the nose, and rounded from right to left. 



Thirdly, the eye in most is very prominent : very nearly one half of 

 the diameter of the ball projects beyond the eyelids. 



In all, I believe that the metatarsus exceeds in length the metacarpus 

 more than it does in most other animals ; but this is much more so in 

 some of this order than in others. It is least so, perhaps, in the mouse : 

 the guinea-pig shows a considerable difference : the rabbit much more : 

 the hare still more : the jerboa of Arabia, and the [helamys] of South 

 Africa are remarkable instances of this disproportion, which gives the 

 hind leg a considerable length over the fore. 



They are all retromingent, and have a considerable glandular appa- 

 ratus for the secretion of a thick mucus about the external parts of 

 generation, both of the male and female. The beaver is a striking 

 instance of this. 



I believe that the females have all 2 two ora tineas. Some of them 3 

 have two vena? cavas superiores, a right and a left ; but this is not 

 peculiar to the present order of animals 4 . 



The caecum, colon, and rectum, are very similar in the whole order, 

 and very different from those of any other animal. 



1 [Hunt. Preps. Nos. 1506 (Coelogenys), 1507 (Lepus).~\ 



2 [The rat, aguti, la paca, are exceptions; but the common uterus in these is 

 extremely short, and the cornua very long, showing the general tendency to the 

 divided oviparous type.] 



3 \_Sciurus cinereus, Pteromys, Mus, Orycterus, Bathyergus, Dipus, Alactaga, 

 Helamys, Echimys, Hystrix, Lepus, Coelogenys. The exceptions observed by the 

 Editor are C'avia Cobaya and Dasyprocta Aguti.] 



1 [It is common to the Lyencephala, and is a structure found in most of the Liss- 

 encephala, and is indicative of the general affinity or tendency of these low-brained 

 groups to the oviparous vertebrata.] 



