140 ANIMAL SKETCHES. CHAP. 



feature in which it differs from that of the bat, is that the 

 wing-membrane was spread from the tip of the fourth 

 ringer (the length of this " little " finger sometimes equal- 

 ling that of the whole body) to the ankle and thence to 

 the tail-tip ; whereas in the bat the wing-membrane is 

 spread on the four fingers of the hand, all of which are 

 greatly elongated. As in the winged reptile, so too in the 

 bat, the membrane swept backward to the ankle and 

 thence to the tip of the tail, a long spur from the ankle 



WING BONES OF DUCK AND BAT. 



aiding in the support of the posterior interfemoral mem- 

 brane before alluded to. 



Quite different again is the wing of the bird. Here, as 

 I need not stay to describe, the arm and shrunken hand 

 bear those exquisite structures, the feathers, which are 

 characteristic of birds, and of birds alone. Indeed the only 

 obvious point of similarity between the membraned-hand 

 of the bat and the feathered-hand of the bird is the compara- 

 tive insignificance in each of the thumb. In the bird the 

 thumb is very small, and carries a tuft of feathers called 

 the bastard wing. In the bat the thumb is similar to the 



