﻿EXTERNAL ANATOMY. SCANSORIAL FEET. 139 



the whole foot, would make us believe that nature was 

 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 

 Oxyurus Dendrocolaptes 

 {fig. 75.), 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 thrown into 

 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 consider- 

 ably shorter, is yet longer than the hinder toe. Here 

 then, a superficial reasoner might be led to exclaim, is 

 a complete refutation 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 Dendrocolapti, 

 notoriously the most typical of all the scansorial creepers, 

 this very toe, which according to our theory should be 

 unusually large, is actually less than any of the others ? 

 The theory, as these critics would declare, and honestly 

 believe, refutes itself ! f A little more consideration, 

 however, will show the absurdity of such a conclusion. 



* This relation of Certhia to Sitta is at once explained by the law of re- 

 presentation, Certhia representing Sitta in the circle of the Certhiance. 



f It is by this sort of partial reasoning that reviewers, altogether ignor- 

 ant of natural history, maintained, upon a former occasion, that we could 

 not possibly be right in asserting that the glossy feathers of the vultures were 

 for defending the skin from blood and offal, because this structure was not 

 found in all the species ; as if all had the same habits,— as if, in short, there 

 were no gradations in nature ! 



