﻿60 



ON THE CLASSIFICATION OF BIRDS. 



Ptilonorhynchus {fig. 17.), as its name implies, has the 

 base of the bill entirely covered with small close-set 

 feathers instead of bristles ; but unfortunately we know 

 nothing of the economy which renders this structure 

 necessary. The second mode in which the nostrils are 

 developed, is almost peculiar to the toucans, and has 

 already been adverted to. The third structure is 

 equally rare, and most developed in that magnificent bird 

 the Musophaga violacea (fig. 33.), or violet plantain- 

 eater : we know not, however, the manner in which 

 this peculiar structure harmonises with the functions 

 of life. 



(57.) We now come to the Bill, or rather to the 

 jaws of birds, the two mandibles of which are merely 

 the jaws of a vertebrated animal lengthened out into a 

 rostrum or beak, analogous to that form which is seen 

 in crocodiles, garfish, and even in long-snouted quad- 

 rupeds. In birds, however, these parts are altogether 

 naked, of a horny substance outside, and are unprovided 

 with teeth, properly so called. The upper of these pieces 

 forms the superior, and the under the inferior, mandible ; 

 while both collectively constitute the bill. It is by 

 this organ that the food is seized, or laid hold of, by 

 ordinary birds, or torn in pieces by the rapacious tribes. 

 The absence of teeth, in such birds as seize their food 

 by the bill, or in which this member has superior 

 powers of prehension, is supplied by a notch, which forms 

 a tooth-like projection close to the point of one or both 

 mandibles : but in some of the rapacious birds, as the 

 sparrow hawk, this process is placed rather more to- 

 wards the middle of the bill, and is rather in the shape 

 of a festoon (fig. 27- a) ; whereas, in the typical falcons 

 (6), the notch is so deep as to produce a sharp tooth-like 

 angle. The owls, on the other hand, have neither the 

 one nor the other of these projections on the upper 

 mandible (c) ; but still the tip is as much curved as in 

 the two former, and the under mandible is toothed. It 

 is almost unnecessary to say how greatly this structure 

 facilitates the operation of tearing and dividing the 



