CHAPTER XXXIV. 
Rodents,— concluded. 
The Hare-Like Rodents. 
Families LAGOMYIDJE and LepopJDAE. 
The whole of the Rodents described in the preceding chapters are characterised 
by having but a single pair of incisor teeth in the upper (as in the lower) jaw; 
and they are hence collectively spoken of as the single-toothed Rodents, or Rodentia 
Simplicidentata. On the other hand, the hares and rabbits, together with their 
cousins the picas, have a second smaller pair of incisors placed behind the large 
front pair in the upper jaw, as shown in the accompanying cut. These Rodents 
are accordingly regarded as con¬ 
stituting a group of equal value 
with the one containing all the 
other families, for which the term 
double-toothed Rodents, or Rodentia 
Duplicidenta, is adopted. In the 
young of this group three pairs of 
incisors are present in the upper 
jaw, but the hindmost pair soon 
disappear, and are not succeeded by 
permanent teeth. In addition to skeleton and teeth of hare. 
these extra incisor teeth, these 
Rodents are characterised by the enamel extending all round the large incisors, 
instead of being confined to their front surfaces. In the skull the palate is 
distinguished by the shortness of its bony portion, in which there are very large 
vacuities in front; while its hinder border is situated between, instead of behind, 
the molar teeth. In all cases the latter teeth have tall crowns without roots, and 
are divided into parallel transverse plates surrounded by enamel. In the hind- 
limb the bones of the lower leg (tibia and fibula) are united together. The upper 
lip is invariably cleft. 
These Rodents, which are divided into two families, are all strictly terrestrial 
in their habits, and have a wide geographical distribution, although more abundant 
in the Northern than in the Southern Hemisphere. 
