﻿124 ON THE CLASSIFICATION OF BIRDS. 



European species, would do well to investigate this subject. 

 Returning, however, to the more perfect examples of this 

 type, we may observe in the common swift (fig. 64, a), 

 that, although all the four toes are directed forward, the 

 two outer, which are the shortest, have a sidelong incli- 

 nation^ something in the same way as our thumb, 

 which, although placed forward like the other fingers, 

 is yet able to grasp an object in a direction very dif- 

 ferent from that which can be accomplished by the 

 others. Of these two lateral toes, the inner one is the 

 true hallux, and it is, like the thumb of the human 

 hand, placed much more backward than the other three. 

 We have not yet found, in any author, certain inform- 

 ation of the manner in which these singular footed 

 birds perch, or rest themselves ; for although we have 

 frequently witnessed their surprisingly rapid evolutions 

 on the wing, their retreats are always in dark caverns 

 or inaccessible heights. We think, from the peculiarity 

 of their feet and their strong prehensile claws, that the 

 swift rests in a semi-perpendicular attitude, clinging, 

 and supported alone by the feet, all of which are, there- 

 fore, anterior, for it is quite obvious they cannot, like 

 ordinary birds, perch upon a branch. The Colies of 

 Africa present us with another instance of this struc- 

 ture ; the toes, indeed, are disposed like those of the 

 swifts, but the feet are obviously intended for walking, 

 which those of the swifts are not: the tarsus, in fact, 

 considering the size of the body, is unusually thick and 

 strong, and nearly as long as in the sparrow : the length of 

 the toes are proportionate, but the two outer (including 

 the hallux) gradually diminish, leaving the inner next 

 in length to that which follows it, and this latter cor- 

 responds to the middle toe of the true perchers : tbe 

 claws of all the toes, although much more slender than 

 those of the swifts, are more curved than in ordinary 

 birds, so that they must be instruments also of protec- 

 tion. The economy of these birds, for a knowledge of 

 which we are indebted to Le Vaillant*, confirms what we 



* Ois. d'Afrique. 



