﻿EXTERNAL ANATOMY. SCANSOR1AL TAIL. 107 



stances so hard and rigid that it appears more like horn 

 than of the ordinary substance. Thus far all scansorial 

 tails are constructed alike, but there are several curious 

 modifications in the other details which deserve our at- 

 tention^ because they serve to characterise different groups. 

 The most typical form is seen in the woodpeckers 

 {fig. 55. a), all of which possess it, with the exception 

 of one type, the genus Asthenurus, represented by the 

 minute woodpecker of Lin- 

 naean authors : in the 

 others, not only the shafts 

 but the webs are unusu- 

 ally stiff, and always show 

 the appearance of being 

 worn at their extremities 

 by their frequent applica- 

 tion to the trunks of trees : 

 all these feathers are lan- 

 ceolate, that is, terminat- 

 ing gradually in a point ; 

 the webs diminishing in 

 breadth as they approach 

 the extremity, but which 

 is never naked ; most of 

 them, also, have the webs on both sides nearly equal. 

 The next modification is seen in the family of Cer- 

 thiadce or creepers, but more especially in the Brazilian 

 genus Dendrocolaptes ; here we find the external shaft 

 very narrow, while the internal is remarkably broad ; 

 both, however, terminate before reaching the extremity 

 of the feather ; so that about a quarter of an inch of the 

 shaft, at its tip, is entirely naked, and the tip itself 

 acutely pointed and inclined downward. This structure 

 will be perfectly understood by the annexed figure (b), 

 while the the abrupt manner in which the broad inner 

 shaft terminates is better seen in the genus Oxyurus. 

 {fig. 56. a.) Now it is quite clear, that a tail thus 

 constructed has equal, if not greater power than that of 

 the woodpecker in assisting a bird to climb, inasmuch as 



