154 ZOOLOGICAL GARDENS. 
distance, and cemented together so as to form a regular 
and uniform structure. 
The first and most essential character of the Order 
to which they belong is obviously derived from the 
great developement of their incisor teeth; and _ this 
peculiarity in structure, as might naturally be expected, 
is connected with a peculiarity in habits equally re- 
markable. So striking indeed is the propensity to 
gnawing, which distinguishes these animals, that many 
later zoologists, of the French school especially, have 
thrown aside the older designation applied to them by 
Linneus, and adopted in its place the expressive name 
of Rongeurs or Rodentia. Of this faculty the Beavers 
appear to exhibit the highest degree of developement : 
their powerful incisor teeth not only serving them to 
strip off and divide the bark of trees, which forms 
their principal nutriment, but also enabling them, when 
urged by their instinct of construction, to gnaw through 
trunks of considerable thickness, and thus to obtain the 
timber of which they stand in need for the building of 
their habitations. These important organs contribute 
therefore in an especial manner to supply them both 
with food and shelter. 
The incisor teeth of the Beavers are two in number 
in each jaw: they are broad, flat, and generally coloured 
of a deep orange or almost chestnut brown anteriorly, 
and pass into acute angles on their posterior surface. 
Their extremities terminate externally in a cutting edge, 
and shelve considerably inwards; for the anterior sur- 
face being alone coated with enamel, and consequently 
offering the greatest resistance, is less easily worn down 
by the action to which they are exposed. Those of 
either jaw correspond exactly with their opposites, and 
the form of the articulation of the lower jaw admitting 
of little or no lateral motion, their action is always from 
