INTRODUCTION. 



or in a soft membrane. The base of the bill is in some 

 birds covered bj a membrane, the cere, in whk^h the nostrils 

 are pierced. The upper edge of the bill is called the culmen, 

 or keel, or ridge; and the corresponding ridge of the low- 

 er mandible, the gonys. The two edges that meet are the 

 margins, and the line of their meeting is the commissure, 

 or gape, which is sometimes overhung by rictal bristles or 

 vihrissse, of various degrees of strength, which assist oc- 

 casionally in holding insect prey. The margin of the 

 upper mandible is frequently notched, or toothed near the 

 tip, and, in some cases, is serrated so as to represent teeth, 

 which are totally wanting in birds. Some tubercles, re- 

 sembling teeth, have been found in the foetus of Parrots, 

 and the horny laminae in the margin of the bill have dis- 

 tinct pulps, like teeth ; and these are the nearest approach 

 to those organs in the class of Birds. 



Feathers consist of the quill, the shaft, and the vane 

 or web ; the last composed of barbs which are themselves 

 furnished with barbules, some of which are also provided 

 with hooked microscopic hairs, which interlock with those 

 of the next and hold them together. They may be divided 

 into clothing feathers, and those subservient to locomo- 

 tion, the feathers of the wings and tail. In many groups 

 of birds the clothing feathers are furnished with an ac- 

 cessory plume fixed to the inner surface of the shaft. 

 This is developed to the extreme in Emeus, so that two 

 feathers appear to be growing from the same root, and in 

 the Cassowary there is a trace of a third shaft in addition. 

 In other birds it is reduced to a small tuft of down. 



In some parts of the body, as over the nares, above the 

 gape, over the eye in a few birds, and in others, on the nape 

 and throat, certain feathers are reduced to mere bristles 

 or hairs of greater or less, strength ; but that these are 



