238 MOSTLY MAMMALS 



of the ordinary skin of the body, which extends outwards 

 between the limbs as far as the wrists and ankles. In 

 addition to the two lateral membranes, there is a narrow 

 and inconspicuous one passing from each cheek along the 

 front of the shoulder to the front of the wrist ; and another, 

 at least in the larger forms, connecting the two hind-legs 

 and involving the base of the tail. 



In general characters the parachute of the scale-tailed 

 flying-squirrels of Africa conforms to the above type ; and 

 a superficial observer might say that the two were in all 

 respects similar. A closer examination will, however, reveal 

 the fact that the parachute in this group is supported by 

 a process of cartilage projecting like a yard-arm from the 

 elbow and extending to the edge of the membrane. As 

 this is present in all the scale-tails (as we may call them 

 for short, especially as they have no right at all to the 

 title of squirrels) and absent in all the true flying-squirrels, 

 it evidently indicates an important difference between the 

 two groups. 

 ^ A further important distinction between them is afforded 

 by the presence on the under-surface of the basal portion of 

 the tail of a series of overlapping horny scales, from which 

 the African group takes both its popular title of scale-tail 

 and its scientific name of Anomalurus. Evidently these 

 scales are intended to aid in supporting the animals as 

 they climb the boughs or stems of trees, and they are 

 thus strictly analogous to the stiff tail-feathers of wood- 

 peckers. 



Yet another difference between the two groups is to be 

 found in the structure of the crowns of their cheek-teeth. 

 In ordinary squirrels the grinding surfaces of these teeth 

 are surmounted by simple tubercles, which in some cases 

 may be elongated into ridges. And a similar type of 



