ANISODACTYLIC FEET. 265 



are not at all adapted for such surfaces, and those of 

 them which have their own peculiar feet in the 

 greatest perfection, are as helpless upon the ground 

 as the swifts. 



But their feet can adhere to, and, with the assist- 

 ance of the wings, move along' any surface, be its 

 form or position what it may. Those which are bark 

 birds can run along the boles of trees, upwards, down- 

 wards, or round by a circular motion ; and others, 

 again, can hang by the feet to the petals of flowers, 

 while the bill reaches the bottom of the nectary, and 

 sips the sweet juice which accumulates there, as is 

 well exemplified in the humming-birds and the nectar- 

 suckers. 



The structure of foot, by means of which this 

 singular command of all manner of surfaces is ob- 

 tained, is apparently a very simple one ; and if we 

 had not so many instances in nature of the cleverest 

 action performed by organs apparently the most 

 simple, we should never imagine that the apparently 

 small difference of structure that there is between the 

 feet of these birds, and the feet of birds which cannot 

 climb at all, could be sufficient to effect so great a 

 difference of action. The ordinary appearance of 

 the foot, when in a state of repose, is three toes to 

 the front, and one behind, the same as in an ordinary 

 walking foot, only the middle and external toe have 

 a union at their bases which appears to be something 

 more than a merely membranous connexion, like that 

 of many of the insectivorous birds. It is, however, 

 in these two toes, their union and the peculiar mode 

 of their articulation, that the whole peculiarity of the 

 foot, that to which it owes its wonderful climbing 

 power, consists. These two toes form a sort of second 

 foot, which can act upon its own articulation in 



