EXTERNAL ANATOMY. SCANSORIAL FEET. 137 
and therefore we find a corresponding diminution in the 
length of the hind toe, which is rather shorter than 
that in the middle ; but addi- 
tional strength is given to the 
claws, all ofwhich arestronger, 
broader, and much more 
curved, than in the genera we 
first noticed : the toes, also, 
are cleft to their base, and tbe 
lateral ones are of the same 
length. Few ornithologists, 
indeed, would suspect these 
birds to be climbers, seeing 
that their feet are of the ordi- 
nary size, and that there is no 
very striking development of the scansorial structure in 
any one part. Nevertheless, we may arrive at this con- 
viction by tlie form and elongation of the hinder toe, 
the strength, curvature, and compression of the claws 
and the diminished flexibility of the tail feathers, when 
compared wdth these parts in ordinary perchers. It is 
at this point of the series that nature determines upon 
a third and new modification of the scansorial faculties. 
In the long-toed nuthatches, first described, she has con- 
centrated this power solely in the feet. In the genera 
Zenopi‘, Anahates, ^-c., it is divided between the toes 
and the claws, some little aid being derived from the 
tail. But in the third modification of these powers, 
which we shall now describe, greater facilities for climb- 
ing are given to all these members, so that we come to 
the highest development of the scansorial faculty in 
birds whose toes are not arranged in pairs. This change, 
however, like aU her other operations in the physical 
world, is marked by harmoniou gradation. The gra- 
dual diminution of the characters last enumerated among 
the more slender clawed Synallaxi, would lead an orni- 
thologist, who merely saw some two or three of the 
species, to suppose they had no connection with this 
family, whereas it is in tllis very genus that nature 
