EXTERNAL ANATOMY. SCANSORIAL FEET. 139 
the whole foot, would make us believe that nature w^ 
giving us a repetition of the structure we have already 
had in Sitta, and that we were again returning to that 
type. But this similarity can be satisfactorily accounted 
for upon other principles* ; and now, for the first time 
we perceive the tail decidedly assuming the scansorial 
structure. Certhia conducts us to its representatives in 
the new world, the genera 
Oxyurtis Dendrocolaptes 
{fig. 7.5.), and both 
of which, in regard to 
their feet, are the same, 
and both differ in this re- 
spect from Certhia as well 
as from all the genera we 
have yet noticed. The 
scansorial powers of the foot, hitherto chiefly i"*" 
the hallux, is now transferred to the foremost toes, the two 
exterior of which are of the same length, and are also 
equal to the tarsus, while the inner, although consuler- 
ably shorter, is yet longer than the hinder toe. Here 
then a superficial reasoner might be led to exclaim, xs 
a complete reftitation of the theory but lately advanced 
on the importance of the long hind toe of the nuthatch • 
for if the great development of that toe was so essential 
to climbing birds, how is it that in the Devdrocolapt,, 
notoriously the most typical of all the scansorial creeper^ 
this very toe, which according to our theory should be 
unusually large, is actuaUy less than any of the others 
The theory, as these critics would declare, and honestly 
believe, refutes itself !t A little more consideration, 
however, will show the absurdity of such a conclusion. 
• Thin relation of Certhia to Sito is at once 
presentation, Crrthia representing SUta circle o „p,thcr ignor- 
^ t It is by this sort of partial reasoning that ''^viewers, altogc^hcr^ 
ant of natural history, maintain^, upon a w 
not possibly he right in asserting that the structure was not 
for defending the skin from blood and oflal, l>ecause thi short, there 
found in at/ the species ; as if all had the same habits,— > 
were no gradations in nature I 
