156 
CHRYSOPTILUS. 
The lateral angle of the upper mandible, instead of 
being close to the margin, as we have seen in Den- 
drolates, is now either a little way removed from the 
culminal ridge, or it is quite close. Now, the re- 
lative powers of picking holes in trees, which all 
these birds possess in different degrees, is always de- 
termined by the position of this singular angle. In 
those birds, which are proverbial for their superior 
powers in this respect, the angle we are speaking of 
is acute, and is nearer to the margin than to the top 
of the bill, which thus as- 
G sumes the form of a sharply 
angulated wedge ( 1), so that, 
but for these angles, the hill 
would be cylindrical ; every 
mechanist knows the superior power of a wedge 
formed with acute angles over another where the 
angles are obtuse (2). Hence it follows, that the 
different sub -genera of Chrysoplilus are much in- 
ferior in the power of breaking wood to those of 
Picus. Some, in fact, frequently feed upon ants. 
They are clearly, therefore, an inferior race, and 
constitute the sub-typical genus of the family. 
And yet, although the characters of the Chry- 
soptili, as a whole, will always prevent them from 
being confounded with any other genus ; the sub- 
genera, or types of form, require much more study 
than we have yet been able to give them. It is 
very clear, however, that the group we shall now 
enter upon is very distinct, not merely from Den- 
drolates, but from the mere typical examples of 
