590 MURIDA—EPIMYS 
somewhat harsh quality to the fur; on the back many of them are stiff, 
broad, flattened bristles, each with a distinct groove along its anterior or 
dorsal surface. In hot countries such hairs are in all rats frequently 
developed as spines. On the back, and particularly towards the 
rump, long black hairs, usually of from 20 to 25, but sometimes 30 or 
40 mm. in length, occur; although these long hairs are a good deal 
more slender than many of the middle hairs, they also contribute 
towards producing a certain looseness and harshness in the appearance 
of the fur. 
Colour:—The colour ranges from uniform dusky to brown, with 
a white or cream belly, and above it is usually darker along the dorsal 
line. Between the extremes every 
intermediate gradation may be 
found. These intermediates occur 
frequently in large towns or ports, 
where, owing to the cosmopolitan 
nature of the rat populations of 
such localities, much crossing prob- 
ably takes place. In more open 
and remote districts the coloration 
conforms usually to one or more 
definite types, and intermediates 
are rare; for details, see below 
under Geographical variation. 
Young:—The pelage of the 
young is relatively soft and full; 
all three kinds of hair can be 
distinguished in individuals with 
a head and body length of from 
78 to 100 mm., but the bristles 
and long dorsal hairs in such 

FIG. g90.—SKULL AND MANDIBLE OF Z/imvys 
vallus (life size). From Miller’s Catalogue 
of Mammals of Western Europe , reproduced 
by the kind permission of the Trustees of 
the British Museum (Nat. Hist.). 
specimens are relatively feeble 
and do not much exceed the 
underfur in length. In the “ wild- 
; coloured” races the coloration is 
generally like that of the adults, although the hue is duller and greyer, 
According to de Isle, the dusky (7 vattus) and the “ wild-coloured” 
( frugivorus) races are distinguishable by colour ten days after birth. 
The adult skull (Fig. 90) compared with that of 2. xorvegzcus differs 
in its smaller size (condylo-basal length 38 to 45 mm., instead of 43-4, 
usually not less than 45, to 54:2 mm.) and lighter build. The brain-case 
is relatively slightly broader; the prominent supra-orbital ridges are 
continued backwards along the parietals, at a relatively low level, as out- 
wardly curving (instead of approximately parallel) crests; the length 

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