72 ZOOLOGICAL GARDENS. 
and externally, by a folding inwards of the outer coat. 
Their tongues are roughened by papille similar to those 
of the cats; their heads generally short and truncate ; 
their nostrils large and open; their ears and eyes com- 
paratively small; and their general form, short, thick, 
and clumsy. 
M. F. Cuvier has lately attempted to subdivide this 
truly natural family mto smaller generic groups, depen- 
dent chiefly on his own theoretic notions of the value 
of the shghtest modifications in the form of the skull 
and teeth in the discrimination of genera. Some varia- 
tions in the number of toes, and still more remarkable 
peculiarities in the structure of the tail are brought 
in aid of this subdivision; but we can scarcely admit 
the justice of his views unless when supported by a 
marked difference in the mode of life, such as exists 
between the burrowing Porcupines of the Old Conti- 
nent, the arboreal species of North America, and the 
prehensile-tailed climbers of the South. 
The name of Hystrix is retained by M. F. Cuvier 
for the Old Continent group, of which the Common 
Porcupine is regarded as the type, and of which it is 
at present the only described species, although it is 
probable that the Indian and South African animals 
which have hitherto been confounded with it may here- 
after be shown to be distinct. The principal discrimi- 
nating character of this group is made to consist in the 
great convexity of its line of profile, the nasal bones 
being developed to an extraordinary degree. The teeth 
are more elevated above the level of the jaw, and less 
irregular in their outline and in the lines of enamel 
upon the surface of their crowns, than those of the 
other genera of the family. On the fore feet there are 
but four distinct toes, the existence of the fifth being 
indicated only by the presence of its claw; on the 
