404 



GENERAL ZOOLOGY 



hairs called vibrissa. At the back of the head are movable 

 flaps of skin (external ears, or pinnae) placed at the opening 

 of the ears. The long and bushy tail is useful in a number 

 of ways : it is an ornament ; it is useful as a balancing or- 

 gan in the long leaps from branch to branch ; and it serves 

 to keep the squirrel warm in its nest in cold weather. 



The Digestive Sys- 

 tem. The mouth is pro- 

 vided with fleshy lips, 

 which assist in seizing 

 and holding food. On 

 the ventral surface of 

 the mouth rests a 

 large, fleshy tongue 

 (Fig. 215), with nu- 

 merous nerve endings 

 of the organ of taste 

 (papillae) scattered 

 over the surface. The 

 front teeth, called in- 

 cisors (Fig. 215), are 

 long, sharp, and chisel- 

 shaped, and are fitted 

 for gnawing ; those in 

 the back of the jaw, separated from the incisors by quite 

 a space, are shorter, broader, and flattened on top, and are 

 fitted for grinding (Fig. 213). The incisors are four in num- 

 ber, two in each jaw ; the grinding teeth in an adult squirrel 

 may be eighteen in number, — four on either side of the 

 lower jaw and five on either side of the upper jaw. Of the 

 grinding teeth the last three on either side in both jaws are 

 termed molars, the others premolars. One of the premolars 

 in the upper jaw is very likely to be minute, or even missing, 

 having been shed in early life. 



Fig. 212. Photograph of a gray squirrel 



