254 STUDY OF NATURAL HISTORY. 
modification of the same structure exemplified in 
all the species of rhinoceros ; while the tusks of the 
elephant are no more than teeth, performing the 
same office, and applied to the same uses, as the 
horns of the ox. Now it is very remarkable, that 
naturalists agree in placing all these quadrupeds 
close to each other ; or rather, in one of the primary 
divisions of the class: so that, with the exception 
of the morse and the monodon, or narwhal, the 
whole ef the horned quadrupeds are found belonging 
to one natural order. This circumstance, of itself, 
is a strong corroboration of the opinion here ex- 
pressed, and should lead us to infer that horns and 
such like appendages indicate one of the essential 
characters of such groups or forms as possess them. 
But where, the student may exclaim, are we to look 
for horns among birds? for, if such appendages 
really constitute, essential characters, they must 
either be found in other vertebrated animals, or a 
structure, limited to one class, can never be ranked 
as one of the primary types of nature. Now, the 
only family of birds which may be said to possess 
horns analogous to what we see among quadrupeds, 
are the hornbills, Buceride, nearly all of which have 
excrescences, as they appear, rising from the front 
of the bill; and one of the species is so remarkable 
in this respect, that it is called the rhinoceros horn- 
bill. Other birds,—as the Tragopan pheasant of 
India, the horned screamer of America, and the 
unicorn chatterer of Brazil,— have hornlike pro- 
tuberances, but they are soft and fleshy. The truth, 
however, appears to be, that horns are represented 
in the feathered tribes by crests, which are not 
