THE HOUSE MOUSE 639 
Field Mouse; the strongly recurved coronoid processes rise slightly 
above the level of the condyles. 
The teeth have been described above under the genus. 
Local variation:—The yellow subterminal bands of the longer 
hairs are usually better developed in outdoor House Mice, which, 
therefore, have a more sandy appearance than those generally caught 
in houses. This fact has long been known, as, to Macgillivray, who 
states (251) that “individuals obtained in the fields are sometimes 
almost as beautifully coloured as the Wood Mouse, there being much 
yellowish-brown on their upper parts, and their lower being of a dull 
cream-colour” ; and to Jenyns, who adds (J/au., p. 32) that they “ some- 
times attain a larger size, measuring nearly four inches in length.” 
The mice described by Jameson (/ourn. Linn. Soc., xxvi., 1898, p. 
405) from the sandhills of the North Bull, Dublin Bay, though differing 
among themselves, are characterised by their very light colour, and may 
be regarded as representing the extreme phase of the yellow outdoor 
coloration ; these mice live on a barren sandy waste, where they are 
exposed only to the attacks of enemies hunting by sight alone; there- 
fore, as suggested by Jameson, it is not unlikely that natural selection 
has played and is playing an important part in the elimination of the 
darker individuals of the colony. 
Adams! (J/S.) has caught tawny bellied House Mice in Surrey and 
Sussex ; these were taken usually in cornfields and hedge-banks—often 
300 or 400 yards from any building, sometimes in ricks at threshing, 
and once or twice in country houses. He notes that the tails were 
often relatively longer than in indoor House Mice. A few years ago 
W. Evans observed that the House Mice living out of doors on the Isle 
of May (Firth of Forth) were lighter in colour than ordinary indoor 
examples; he sent one of these to Barrett-Hamilton. It seems probable 
that the original colour of wild JZ. musculus was some shade of yellow 
or tawny; and that in this case, as Adams suggests, the tawny hue of 
present outdoor families may be explained either as a reversion to 
type, if such families have descended from a domestic stock, or as a 
retention of the ancestral coloration, if they have always been feral. 
In either case the difference between the indoor and outdoor coloration, 
whatever its “protective” value may be, is probably to be explained 
as a result of the wide difference in the light intensities to which the 
two stocks are respectively exposed. 
Kinnear (Anu. Scott. Nat. Hist., 1906, 65) describes the House Mice 
of Fair Isle as being rather larger and more tawny in colour than main- 
1 Adams (47S.) “noticed very markedly in the sunny summer of 1911, that the 
coats of the Common Shrew were lighter in colour than usual. There was much 
more albinism in ears than usual—about 25 per cent. had white ears in that year, 
whereas about 4 per cent. is the normal condition.” 
