PERCHING BIRDS. 147 
\ 
Zi 
Fig. 122.—Rhinoceros Horn-bill. 
a 
v4 
with its appendage, is not as heavy as it appears, for its 
structure is of a light, honeycomb character. The upper 
protuberance is hollow, and it is supposed that it serves 
as a sort of sounding-board, to give by its reverberations 
force to the roaring cry of the bird. There are several 
species found in India and Africa. 
245. Of the division of the Perchers called Dentiros- 
tres, or Tooth-billed, there are five families: the Shrikes, 
or Butcher-birds, Warblers, Thrushes, Fly-catchers, and 
Chatterers or Waxwings. The notch in the upper man- 
dible which makes the tooth-like projection, § 234, is not 
always deep, and is sometimes wanting. In such a case 
the proper place of the bird in the classification is known 
by its resemblance in other respects to the true tooth- 
billed species. There are some, indeed, whose charac- 
teristics are so intermediate between the Conirostres 
and the Dentirostres, that zoologists differ as to the 
