SQUIRRELS, BEAVERS, DORMICE, AND RATS 225 



Family: SCIURID.E. THE SQUIRRELS 



The squirrels and marmots are a closely allied group exhibit- 

 ing very varied modes of life. Some almost fly, and many are 

 wholly arboreal, while others never leave the ground or burrow 

 and live beneath its surface. 



Sciurus vulgaris. The Common Squirrel 

 In this charming little animal, the teeth, as in most squirrels, 

 consist of the single pair of incisors in the upper and lower jaws, 

 one or two pairs of premolars in the upper jaw and one pair in the 

 lower, and three pairs of molar teeth in both jaws. The molar 

 teeth of the squirrels are remarkable in that they present perhaps 

 more archaic features than can be met with in other groups of 

 Rodents, their crowns being still marked by tubercles and retaining 

 roots (see p. 238). The incisor teeth, as is the case with so many 

 Rodents, are stained a chestnut colour. In the hind limbs of the 

 squirrel there are five functional toes, but in the " hands " there 

 are only four fingers, for the thumb is marked by little else than 

 a claw. In the toes and fingers the terminal joints are crooked, 

 and armed with long, curved, sharp claws admirably adapted for 

 clinging tightly to the bark of trees. The number of teats in 

 the female varies from two to three pairs, and they are situated 

 along the abdomen. The tail is long — indeed, nearly as long as 

 the body. From the tip of the nose to the base of the tail an 

 average male squirrel measures just over 8 in., while the tail 

 from its base to the end of the bone measures 7 in. The tail 

 is somewhat heavily plumed on either side, though the thickness 

 of these long hairs varies according to season, being more abun- 

 dant in winter than in summer. When sitting up on its hind 

 legs in repose the tail usually coils over the back, but is always 

 stretched out behind when it is in movement, sometimes quite 

 straight, at other times slightly curved. The nose is rather 

 arched, the upper lip is cleft, the eye is large and full, and the 

 ears are rounded, wide, and of considerable size. This circular 

 outline of the outer ear is disguised during the winter months by 



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