142 ON THE CLASSIFICATION OP BIRDS. 
although this part of our subject has expanded itself to 
wider limits than were originally anticipated. The first 
of tliese is seen in the singular and rare genus Orthonyx, 
one of the very few scansorial birds of Australia, and 
which seems to partake of the anomalous, or rather 
unusual structure so prevalent among the animals of 
that region. It will he necessary, however, before we 
can understand how a bird like Orthonyx, — whose great 
and long foot resembles that of the rasorial order, — can lie 
connected with Dendrocolaptes, that we look to the genus 
Selerurun (fig. 76.), an equally rare type, from the forests 
of Brazil, and of 
which the only 
specimen we 
have yet seen is 
in our museum. 
The foot of this 
bird has much of 
the general cha- 
racter of Dendro- 
cotaptes, but the 
tarsus is much longer, and the outer toe (a), instead of 
being equal to the middle one (b), is shorter ; the claws 
are also smaller, weaker, and less curved : in all this dimi- 
nution of the scansorial powers in tliese parts, we see a 
considerable falling off from the typical perfection, and 
adverting to what we have just advanced on the use of 
the anterior feet, it is obvious this bird cannot ascend a 
tree so rapid as a Dendrocolaptes. The same dimi- 
nution of strength can be traced in the tail, the shafts 
of which, although rigid, are comparatively weaker, 
and do not extend beyond the webs, as in all the rest of 
the Certhianai. Yet still, as this bird belongs to the 
pre-eminent group of the tree creepers, its powers 
should not be so very much diminished ; and we con- 
sequently find that the comparative weakness of its 
other members is made up by a great elongation of the 
hinder toe (c), which is one half as long again as in Den- 
drocolaptes (fig. 75.), so that it becomes, as in the nut- 
