s of rodents are composed of
dentine coated in front with a layer of hard enamel, the other
surfaces being without this protection, except in the case of some,
amongst which are the hares and rabbits, which have a thin coating
as well all over. These forms are those with rudimentary incisors,
and constitute the links connecting the other mammalia with the
Gnawers.

The molars are much alike in structure, and can hardly be divided,
as they are by some naturalists, into molars and premolars. They take
the three hindmost as molars, regarding the others as premolars.
Sometimes these grinders have roots, but are more commonly open at
the end and grow from a permanent pulp. They are composed of tubular
and convoluted portions of enamel filed up with dentine, and their
worn surfaces show a variety of patterns, as in the case of the
Proboscidea. These enamelled eminences are always transverse, and
according to Cuvier those genera in which these eminences are simple
lines, and the crown is very flat, are more exclusively frugivorous;
others, in which the teeth are divided into blunt tubercles, are
omnivorous; whilst some few, which have no points, more readily
attack either animals, and approximate somewhat to the Carnivora.

The head is small in proportion to the body, the skull being long
and flat above; the nasal bones are elongated; the premaxillaries
very large on account of the size of the incisor teeth, and the
maxillaries are, therefore, pushed back; the zygomatic arch is well
developed in most, but is in general weak; the orbit of the eye is
never closed behind; the tympanic bulla is very large; the jaw is
articulated in a singular manner; instead of the lateral and
semi-rotary action of the Herbivora, or the vertical cutting one of
the flesh-eating mammals, the rodent has a longitudinal motion given
by the arrangement of the lower jaw, the condyle of which is not
transverse, but parallel with the median line of the skull, and the
glenoid fossa, or cavity into which it fits, and which is situated
on the under side of the posterior root of the zygoma, is so open
in front as to allow of a backwards and forwards sliding action. The
vertebral column is remarkable for the great transverse processes
directed downwards, forwards, and widening at the ends. In the hare
these processes are largely developed; the metapophyses or larger
projections on each side of the central spinous process are very long,
projecting upwards and