Glass 6. Mammalia. Order 12. Rodentia. 529 



is a longitudinal groove^ so that the mandible possesses considerable 

 mobility from before backwards' (in masticating, the lower jaw moves 

 backwards and forwards ; the enamel stripes upon the molar run in 

 the opposite direction, i.e., transversely). The feet are usually small 

 and bear claws, and the animals are generally plantigrade. The first 

 digits of the manus are rudimentary or absent, whilst the other 

 fingers and toes are usually all present. In several forms there are 

 internal cheek-pouches, outgrowths of the cheeks, connected with 

 the buccal cavity ; in some, in approximately the same position, there 

 are ingrowths of the skin covered with hairs (external cheek- 

 pouches) .* 



The Eodents are widely distributed and rich in species, includ- 

 ing for the most part small forms which are almost exclusively 

 herbivorous. 



1. The Rabbit family {Leporidm). i f , m ^-^, the large upper 

 incisors are gi'ooved, the molars are plicate and grow from persistent pulps. The 

 genus Lepus, with m f , long pinn» ; very short tail ; long hind limbs ;t 

 comprises the Hare {L. i?t(.rqp«Ms),]: distributed throughout the greater pai-t 

 of Europe: and the Polar or Variable Hare {L. timidus or variabilis), 

 in the Northern parts of Europe and Asia, in Ireland, the Alps and the Pyrenees ; 

 it is white during winter in the colder regions : also the shorter-legged burrow- 

 ing Rabbit (i. cMmicwfes), indigenous to South Europe ; the Pika (Lagomys), 

 with m ^ ; short pinns ; shorter limbs than the Hares ; ecaudate ; in Siberia and 

 North America. 



2. The Squirrel family (Sciuridx). m f, tuberculate or plicate; the 

 anterior molars of the upper jaw very small ; poUex rudimentary ; tail hairy : 

 the Squirrel (Sciurus vulgaris), with long, bushy tail; arboreal: the 

 Plying Squirrel (Pieromys) , characterised by the possession of a patagium 

 between the fore and hind limbs (one European species, Pt. volans, in North 

 Russia). The Marmots (Arctomys) ai-e fossorial, hibernating animals; they 

 ai-e thick- set, with short pinns and a short tail : there are two European species, 

 the Alpine Marmot {A. marTnota), and an allied form, the Pouched 

 Marmot (Spermophilus citillus) of East Europe. Allied to the Squirrels is 

 the Beaver {Castor fiber), a fair-sized animal with f plicate molars; short 

 ears ; large, flattened, scaly tail ; and webbed toes on the hind feet : they are 

 excellent swimmers and diggers, and feed upon bark. Beavers were formerly 

 abundant in the British Isles, but are now quite extinct; they occur on the 

 Continent, and are, for instance, still faii-ly abundant in the Elbe : an allied 

 species (C. canadensis) occurs in North America. 



3. Dormice [Myoxidx). M %, with transverse bands of enamel; poUex 

 rudimentary ; tail long and hairy : superficially' they somewhat resemble Squirrels 

 or Mice. The small, mouse-like Common Dormouse {M. avellanarius) 



* In the maxiUse of Mammals generally, there is a shorter or longer canal, the 

 canalis infraorlitalis, through which a large nerve (the maxillary branch of the 

 trigeminus) runs. The canal opens in front of the orbit by a perforation termed the 

 infraorbital foramen. In the Rodents the infraorbital canal is quite short, and 

 usually very wide, and a portion of the masseter muscle passes through it. 



+ The soles of the feet appear to have a complete covering of hair, but as a matter 

 of fact there are small, naked, plantar cushions, which are, however, covered by the 

 hair of adjacent regions. 



t In many books this is incorrectly termed L. timidus. 



M M 



