RODENTIA III

that they may not only be looked upon as ancestral
to the land and water carnivores, but to the in-
sectivores as well, besides filling the gap between the
living carnivores and the marsupials.

RODENTIA. — The rodents are the most
numerous of the mammals. There are quite 1,000
species of them, and their representatives are in
multitudes. They are easily recognised by the long
curved chisel-shaped incisor teeth, and by the hairy
pad which projects from the outside skin into the
mouth behind the incisors in such a way as to keep
the mouth clear of the dust and chips produced by
gnawing. Rodents are conveniently divided into two
sub-orders—those with only two incisors in the upper
jaw, and those with four ; no rodent having more than
two incisors in the lower jaw; and no rodent has
canine teeth.

To the first sub-order, the S7zmplicedentata, belong
the squirrels, the mice, and the porcupines; to the
other, the Duplicidentata, belong the hares, both tailed
and tailless. Among the squirrel-like rodents are
included the flying squirrels, the marmots, and the
beaver. The flying squirrels of Europe, Asia, and
North America have their parachute-like membranes
extended from the wrist ; those of Africa have them
starting only from the elbow. In another respect the
Africans differ markedly from the rest, for they have
a series of scales at the roots of their tails, with which
they are said to cling to the bark of the trees they
climb. These African squirrels belong to a distinct
family, the Anomaluride ; the true squirrels, with no