580 Vertehrata. 



occurs in Britain, and is widely distributed over tlie Continent. Several other 

 species are met with in southern, or southern and eastern Eui-ope : the Squirrel- 

 tailed Dormouse (Jf. jrKs), the largest species : the Garden Dormouse 

 (M. nitela): the Tree Dormouse (M. dry as). Allied is the Sminthus 

 hetulinus or vagus, in North and East Eiwope, very like a Mouse externally, with 

 m f. The Sminthus is closely allied to the Jerboa (Dipus), which is chiefly 

 characterised by the great length of the hind foot ; this especially affects the 

 second to the fourth metatarsals, which are fused (the first to the fifth toes are 

 small or absent) ; the animals hop along, stepping only upon the second, third, 

 and fourth toes of the hind foot ; the tail is long, with a tuft of hairs at the end : 

 desert animals ; South Russia, Asia, Africa. Also allied to the Sminthus is the 

 blind, earless, and tailless Mole-rat {Spalax typhlus), -whose habits are some- 

 what similar to those of the Mole ; South-East Europe (e.g.. South Russia) and 

 Western Asia. 



4. Mouse Family (Muridx). ilff (occasionally |, c/., p. -528); very varied 

 in structure ; tail longer or shorter, scaly ; pollex rudimentaiy. Usually of small 

 size. 



(a) Rats and Mice {Mu.i). Molars tuberculate, with short crowns and 

 with roots ; tail long, slightly hairy ; pinnse fairly well developed. In England 

 occur: the Wood Mouse, or Long-tailed Field M one e (M. sylvaticus), 

 and the Harvest Mouse (M. minutns) -. the following have invaded and live in 

 human dwellings: the House Mouse (M. musculus), the Black Rat (Jf. 

 ratius), now rare, having been almost completely exterminated by the more 

 recent immigrant, the Brown Rat (M. deeumanus). Allied to the Mice is the 

 brightly-coloured Hamster (Gricetus frumentarius), with cheek pouches and 

 short tail ; somewhat larger than a Rat : Central Eiu-ope. 



(6) Field Mice (Arvicola). Molars long, growing from persistent pulps, 

 with deep grooves on each side (gi-inding surface with loops of enamel) ; occasion- 

 ally there are short roots ; tail shorter and more hairy than in the Mice ; pinnae 

 short. They burrow in the ground, and are more exclusively herbivorous 

 (feeding upon roots, bark, etc.) than the true Mice. The following species 

 occur in England: the Bank-vole (A. glareola), •which. aSoria a transition to 

 true Mice ; the molars with short roots ; pinnae and tail somewhat longer than in 

 the rest: the Field Mouse (A. agrestis and arvalis) : the Water Rat 

 (A. amphibius) ; the latter is the size of a Brown Rat, the others about as large 

 as the House Mice. Closely allied is the Lemming (My odes lemmus), with very 

 short tail, and strong claws on the fore limbs ; Scandinavia ; famed on account of 

 its migrations. Another form allied to the Field Mice is the Musquash or 

 Musk Rat (Fiber zibeihicus), with long, compressed tail; the toes with stiff 

 hairs at the edges; furry animals of fairly large size, inhabiting northern 

 North America, and by their mode of life recalling the Beaver. 



5. Hystricomorpha, a group consisting of numerous forms, differing very 

 much externally, but agreeing chiefly in the characteristics of the skull.* Molars 

 }, banded, with roots, or growing from persistent pulps. 



(a) The C o y p u (Myopotamus coypu), an aquatic animal of beaver-like 

 appearance, but smaller, and with a rounded tail ; the toes of the hind foot are 

 webbed ; South America. 



(6) Porcupines (Bi/sfricife), characterised by the modification of some 

 of the hairs into stiff spines, often of enoi-mous thickness and considerable 

 length ; animals of considerable size. The Common Porcupine (Hystrix 

 crisiata), in South Europe ; lives in holes in the ground; tail short. In America, 

 there are various arboreal forms, (Cercolabes) with pi-ehensile tails. 



* E.g., th,e infraorbital foramen is huge, and the mandiblf is peculiar in forni. 



