62 
ON THE CLASSIFICATION OP BIRDS. 
thus to be found only in the two typical orders of 
birds, the Raptores and the Incessores j in aU others it 
is entirely wanting. There is yet a third mode by 
which nature supplies the deficiency of real teeth to 
the bill of birds; and 
that is, by dividing the 
edges into a number of 
saw-like notches, of 
greater or less size as 
the peculiar habits of 
the birds require. The 
first developement of 
this structure is seen 
in the double-toothed 
falcons, as in the genus 
Harpngus {fig. 28. a); 
the next is in the ty- 
pical trogons (6), and 
in the suh-genus An- 
dropadus* (c) : a fur- 
ther advance is seen in the toucans and hortihiUs, where 
the serratures, although coarse and wide apart, extend 
the whole length of the bill : but the highest develop- 
ment is exhibited in the Chizeerhis variegata (d), 
where the teeth are small, shar]), regular, and of equal size. 
IniheMusaphaga violacea {fig. 29.), on the other hand, 
they are somewhat un- 
equal, and nearly obsolete 
towards the base of the 
cutting margins. We 
cannot, unfortunately, il- 
lustrate any one of these 
structures by detailing 
corresponding traits in 
the economy of the birds. 
There is one, however — 
the plant-cutter of Chili — whose bill is described as much 
* North. Zool. vol. ii. p, 485. The Importnn of Lc Vaillant (Ois. d’Af. 
pi. 106. f. 2.), but recently described as a now bird by Jardin and Selby under 
the name of Trkhophorus brachypodiohies. III. of Om. pi. 128. 
