380 
VERTEBRATA. 
BEAVER. — (See p. 33S.) 
not seem to have been greatly prized — and knowing this fact, were accustomed to bite off the 
part that yielded it ! 
This animal is furnished with two incisors and eight molars in each jaw, twenty in all; and is 
particularly distinguished from all the rest of the rodentia by a broad horizontally-flattened tail, 
which is nearly oval and covered with scales. There are five toes on each of the feet, but those 
of the hinder ones — somewhat resembling those of a goose — only are webbed, the webs extending 
beyond the roots of the nails. The second toe of these last is furnished with a double nail, or 
rather two, one like those of the other toes, and another beneath it, situated obliquely, with a 
sharp edge directed downward. There is also a less perfect double nail on the inner toe of the 
hind-feet. 
The incisor teeth of the beaver are broad, flattened, and, as in most of the order, protected an- 
teriorly by a coat of very hard orange-colored enamel, the rest of the tooth being of a compara- 
tively soft substance, whereby a cutting, chisel-like edge is obtained; and, indeed, no edge-tool, 
with all its combinations of hard and soft metal, could answer the purpose better. In fact, the 
beaver's incisor tooth is fashioned much upon the same principle as that followed by the tool- 
maker, who forms a cutting instrument by a skillful adaptation of hard and soft materials till he 
produces a good edge. But the natural instrument has one great advantage over the artificial 
tool; for the former is so organized that as fast as it is worn away by use, a reproduction and pro- 
trusion from the base takes place, and thus the two pairs of chisel-teeth working opposite to each 
other are always kept in good repair, with their edges at the proper cutting angle. When in- 
jury or disease destroys one of these incisors, its opposite, meeting with no check to resist the 
protrusion from behind, is pushed forward into a monstrous elongation. So hard is the enamel, 
and so good a cutting instrument is the incisor tooth of the beaver, that, when fixed in a wooden 
handle, it was used by the Northern Indians to cut bone, and fashion their horn-tipped spears, 
cfec, till it was superseded by the introduction of iron, when the beaver-tooth was supplanted by 
the English file. 
The power of these natural tools is such, that a beaver will bite off" a sapling of the size of a 
