180 ZOOLOGICAL GARDENS, 
With the true or tree Squirrels, familiarly known to 
us by means of the common species that so abundantly 
inhabits our native woods, Linneus associated several 
other groups of animals, some of which, the Dormice 
for instance, have subsequently been distinguished by 
common consent, while the rest are still regarded by 
many naturalists as forming part of the same genus. 
In fact, were we to rely upon the teeth alone as fur- 
nishing the means of subdividing an imconveniently 
extensive group, we should be compelled to leave in 
connexion with the Squirrels many species which differ 
from them most essentially, not only m certain modifi- 
cations of their outward form, but even in the still more 
important characters of their habits and mode of life. 
Thus although we find no appreciable differences in 
dentition between the Tree Squirrels, the Ground Squir- 
rels, the Flying Squirrels, and the Guerlinguets, we 
cannot avoid seeing that there exist other distinctions 
which, combined with the striking discrepancies in 
their manners, are fully sufficient to justify us in re- 
garding each of these divisions as forming a distinct 
group. We are consequently compelled to treat of the 
Squirrels in general not as a genus but as a family, 
divided into the four genera just enumerated, to which 
may perhaps be added a fifth for the reception of the 
Flying Squirrels of the Asiatic Islands, whose dentition 
is said to present a slight variation from the form com- 
mon to all the other species of the tribe. 
In all the other Squirrels the lower incisors are long, 
slender, directed forwards, and much more narrow and 
compressed than the upper, which are strongly curved. 
The molars are four on each side of either jaw, and 
nearly equal in size, with their crowns surmounted by 
elevated lengthened tubercles, variously disposed in 
those of the upper jaw, and in the lower forming on 
