486 
THE LIVING WORLD. 
striking, it is an intelligence whose limits are very narrow. The stomach is 
simple in its structure, and the intestinal canal proportionately favored. I he 
provision for acute hearing, clear sight, quickness of scent, and delicacy of touch 
is as notably great as one would expect from the lives which the rodents are 
to live. To illuminate all this verbal description, let the reader think of an 
example of each of the four families—the hares, the porcupines, the rats and 
mice, and the squirrels. The one fossil rodent , (if, as many naturalists believe, 
it is a rodent ) is the Mesotherium Cristatum, belonged to the Pliocene Age, and 
dwelt in the South American Pampas. In the lower jaw, it had two small supei- 
numerarv incisors, the teeth were enamelled on all sides, and hence wore down 
more like those of 
the eqiiidcc than 
like those of living 
rodents. The mo¬ 
lars are ten above 
and eight below', 
four in the upper 
jaw and tw o in the 
low^er,being simply 
pre-molars ; they 
have no roots. 
The skull is large 
and stout; and the 
feet, though five- 
clawed, are hoof¬ 
like ; in the latter 
particular, as well 
as in the gigantic 
size of the animal, 
the height of w T hcse 
skull w r as a full 
foot, seem to re¬ 
late the mesothe- 
rium to the toxo- 
dontia . Whether 
or not the meso- 
. _ . ., therium was the 
earth hog (Orycteropus capensis). . , r ,, 
Adam of the ro¬ 
dents, it is quite certain that it represents a less differentiated type than is 
found in existing species. Its remains, like those of the monotremes , mar¬ 
supials and edentates , will interest such visitors to our museums as care to 
make real to themselves the resemblances and differences between earlier forms 
and the varieties which have been evolved from these. 
Passing now to existing rodents, we shall consider first the Leporidse, or 
Hare Family, which has the two-fossil forms of Palaeologus and Titanomys, 
corresponding to the tw^o branches of the hare family —the hares proper and 
the hare- like animals. There is an extra pair of “milk” incisors in the 
upper jaw, and the enamelling is such that the teeth do not get the edge 
which is found in rodents, other than the hares . Externally, the hares are dis- 
