638 MURIDA—MUS 
and do not afford any noticeable contrast with the general tint of the 
back. The tail is usually dull brown, both above and below, but some- 
times the under surface is slightly the paler. 
The young in first pelage hardly differ from the adults in general 
colour ; their coat is a little softer and closer, consisting chiefly of the 
woolly underfur. 
The skull (Fig. 93) compared with that of the Field Mouse is dis- 
proportionately small and peculiarly flattened. In correlation with the 
small size and weight of the brain (see p. 566 above), the broadly ovate 
brain-case is depressed, its depth being relatively little greater than that of 
the rostrum. The interparietal is large and rectangular, and it belongs 
wholly to the occipital region, the lambdoidal crest and suture passing 
in front of, instead of behind it, as in A. sylvaticus. The interorbital 
region is broader than the rostrum; its edges are square and not 
beaded, and the temporal crests, which are their backward continua- 
tions on the sides of the brain-case, are very feebly developed. The 

(2) (3) 
FIG. 93.— SKULLS OF Mus musculus (1) dorsal, (2) ventral ; AND Mus muralis (3) ventral; x 14. 
zygomatic arches are relatively strong, and their greatest breadth 
usually falls just in front of the glenoid articulations; the vertical 
anterior border of the masseteric plate is situated distinctly in advance 
of the roof of the infra-orbital canal, and at its base there is a quite 
small, but prominent peg-like process, from which the tendon of the 
anterior part of the masseter muscle takes its origin. The incisive 
foramina are greatly narrowed behind; they are of remarkable length, 
and terminate posteriorly about opposite the middle of wz. As in 
Micromys, the palatal shelf extends backwards behind the tooth-rows 
for a short distance; iti this region it shows also a slight median 
ridge, which is frequently channelled by a weak longitudinal ventral 
groove. The mesopterygoid fossa is of moderate length, wider behind 
than in front, where it terminates squarely. The pterygoids are 
straight, and their hamular processes barely meet the moderately large 
auditory bulla. The nasals extend forwards but little in advance of 
the front faces of the incisors. 
The mandible is slightly shorter and deeper relatively than in the 
