866 



posteriorly, finely tuberculate anteriorly ; plantar tubercles 

 small, widely- spaced, without noticeable contrasts in size or form, 

 the two anterior slightly the largest, the postero-external slightly 

 the smallest, their outlines ovate or nearly circular ; a small but 

 distinct supplemental tubercle at outer margin of tubercles lying 

 at base of first and fifth toes. Claws simple, curved, those on 

 hind feet slightly the larger. Tail about as long as head and 

 body, sometimes a little longer, rarely much shorter unless 

 injured, its diameter at base about 3 mm., its tip not so 

 slender as in Apodemus sylvaticus ; annulations well defined but 

 narrow, about twenty-two to the centimeter at middle, the boun- 

 daries of the individual scales obscurely marked ; hairs rather 

 numerous but not concealing annulations, and not forming pencil, 

 their length equal to about width of two and a half rings. Fur 

 soft throughout, the grooved hairs so slender as not to suggest 

 bristles in texture. Mamms : p 3 — 3 ; i 2 — 2 = 10. 



Colour. — Upper parts a light, dull wood-brown, irregularly 

 darkened with slaty and blackish along back, faintly more buffy 

 on sides, the general effect not far from the broccoli-brown of 

 Ridgway, but usually with a peculiar dusky cast ; underparts 

 essentially like sides or a little more yellowish, the line of demar- 

 cation absent or very obscure ; bases of hairs everywhere slate- 

 grey, this colour usually appearing at surface on chin and throat, 

 where it produces a smoke-grey or drab-grey effect ; ear dull 

 brownish, the outer side of anterior border usually darker ; feet 

 drab or dusky, not contrasting with back ; tail dull brownish 

 throughout, occasionally lighter below than above. 



Skull. — As compared with that of small European Muridse of 

 other genera, Micromys excepted, the skull of Mus musculus is 

 immediately recognizable by its small size. Its general form is 

 characterized by a peculiar flatness not 

 found in any of the others. Dorsal 

 profile slightly convex throughout, the 

 nasals sloping forward at an angle which 

 causes an evident break in the general 

 curve ; occiput low, somewhat obliquely 

 truncate, so that the entire supraocci- 

 pital between lambda and foramen 

 magnum is visible when skull is viewed 

 from above ; ventral profile faintly con- 

 cave ; contrast between depth of brain- 

 case and rostral depth noticeably less 

 than in Apodemus sylvaticus. Brain-case 

 short-oval in outline when viewed from 

 above, with a slight though evident ten- 

 dency toward squaring behind and in 

 front. Interparietal rather large, its area nearly equal to that 

 of one parietal, its general form ligulate, the anterior border pro- 

 jecting forward at middle, the lateral extremities almost squarely 



Fid. 177. 

 Mus musculus. Nat. size. 



