336 VERTEBRATE ANIMALS. 
is tufted. The Royal Tiger is exclusively Asiatic, as are most of 
the Tiger-cats, but some of the latter are American. The 
Spotted Cats or Leopards are represented, among others, by the 
Leopard and Cheetah of the Old World, and the well-known 
Jaguar of the American Continent. The Puma is also American, 
but its colour is uniform. The Lynxes are distinguished by 
their tufted ears, and are found both in the Eastern and Western 
hemispheres. 
ORDER X. RODENTIA—lIn this order are a number of small 
animals, characterised by the absence of canine teeth, and the 
possession of two long curved incisor teeth in both jaws, which 
are separated by a wide interval from the molars (fig. 182). 
WHY. 
ULL LL 
aia 2 
Wy ap =— 
GLEE. 
Fig. 182.—A, Skull of the Beaver (after Owen); B, Diagram of one of the incisor 
teeth of a Rodent, showing the chisel-shaped point. a Enamel; @ Softtooth- 
substance (dentine). 
There are seldom more than two incisors in the upper jaw 
(sometimes four), but there are never more than two in the 
lower law. The molar teeth are few in number (rarely more 
than four on each side of each jaw). The feet are usually fur- 
nished with five toes each. 
The most characteristic point about the Rodents is to be 
found in the structure of the incisor teeth, which are adapted 
for continuous gnawing. They grow from persistent pulps, 
and consequently continue growing as long as the animal lives. 
They are large, long, and curved, and are covered in front with 
a layer of hard enamel, so that the softer parts of the tooth are 
placed behind (fig. 182, B). The result of this is, that as the 
tooth is used in gnawing, the softer parts behind wear away 
more rapidly than the hard enamel in front, and thus the crown 
