THE FLIGHT OF BATS 



293 



bat's wing and umbrella fold up in a similar way. The steering 

 membrane is supported on either side by a gristly spur which 

 projects from the ankle. 



Examination of a Bat's skeleton (fig. 830) brings out some of 

 the peculiarities more clearly. It will be seen that the fingers, in 

 spite of their length, only possess three supporting bones apiece, 



Fig. S29. — Pipistrelles {Vcsperugo pipi^treUus) 



the usual number among Mammals. As in all cases where the 

 fore-limbs have free lateral movements, there are well-developed 

 collar-bones, propping up the shoulders from the inner side. 

 There is a prominent ridge or keel running along the sternum, 

 and correlated with the existence of large pectoral or breast- 

 muscles, the principal agents in moving the wings. The hind- 

 limbs are turned backwards in a remarkable manner, and the 

 size of the flying-membrane is therefore greater in that direction 

 than would otherwise be the case. 



The parachuting arrangements in a Colugo (see p. 282) afford 



