576 MURIDA—EPIMYS 
The skull is strongly built, with well-marked supra - orbital 
ridges, which generally extend back to the outer corners of the 
inter-parietal ; the front edge of the zygomatic plate is always 
convex ; the posterior border of the palate is a simple shelf; 
the pterygoids are thin plates, and the pterygoid fosse are 
deep and well defined. The incisors are much deeper than 
broad, and their wearing surfaces are normal and unnotched. 
The cheek-teeth (PIl. XXVIII., Figs. 8 and 9) are character- 
ised by the complete suppression of cusps 7 and 3 in upper 
molars, which have consequently never more than three outer 
and two inner tubercles. The tubercles show a_ nearly 
transverse arrangement, and because of this and the more or 
less relatively large size of those forming the median row, 
the teeth, in the higher species, acquire something of a 
lophodont or laminated character—a feature which becomes 
better marked in certain more highly specialised Oriental 
relatives, e.g. Mesokia. m- are never longer than the combined 
length of #2 and $; m3 show no tendency to disappear. 
The mamme vary from six to twelve or more; typically there 
appear to be three pectoral and three inguinal pairs, and, so far 
as is known, at least one pectoral pair is present in all species. 
The young, born naked, soon acquire a soft, thick, and mole- 
like pelage, in which as a rule the dense underfur is grey ; 
their colour is largely dependent upon this underfur; the 
upper parts are therefore greyer than in adults, and the belly is 
dark grey. The moult appears to take place usually in a gradual 
and inconspicuous manner, but in some Indian specimens of 
the vatéus group the new fur of the rump is sharply separated 
from the old coat remaining on the head and shoulders. 
The true rats may be regarded as the most successful of 
existing terrestrial mammals. Their activity, intelligence, 
prolificacy, and power of procuring and assimilating a great 
variety of foods are all of a very high order. The higher 
species are at home in all climates and under all conceivable 
conditions, except perhaps extreme cold. They accompany 
our ships to sea, and swarm in our houses. Although highly 
palatable, their cautious and cunning habits, their vigorous 
courage and high powers of defence and offence, enable them 
to attain a size which would be fatal to the continued existence 
a 
