THE BILL 



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about equal width throughout; clavate, or cluh-shaped ,^^ indi- 

 cates an enlargement at the end nearer the tip of the bill, and 

 ovate ^^ at the end nearer the base of the bill. An oval ^' nostril 

 is widest near the middle and wide for its length, while an 

 elliptical ^* one is narrower. If the nostril is about as wide as 

 long, it is called circular ;^^ if there is a raised border to the 

 circular nostril, it is called tnbidar.'-^' 



Appendages to the nostrils. — The usual plan is to have the 

 opening through material like the covering of the rest of the bill, 

 of soft skin in the snij^es, and of horn in the sparrows. Some- 

 times there is a special piece of about the same material as the 

 bill either above or below the nostril, called a nasal scale.-^ A 

 more frequent appendage consists of feathers proper or bristle- 

 tipped feathers. These are usually frontal feathers, more or 

 less changed into bristles, often entirely filling the nasal fossae, 

 and frequently so covering the base of the bill as completely 

 to cover the nostrils.^ This is well seen in the crow and in 

 the blue jay. 



Sometimes the nostrils have special feathers of their own. 

 If these are separated and quite feather-like, they form 7iasa,l 

 tiijls.^ When not separated but extending from side to side, 

 they form a ruff.-^ Those feathers or bristles which are turned 

 forward are called retrorseP 



Other appendages to the bill. — The base of the bill is, in 

 hawks, etc., covered by a special membrane extending beyond 

 the nostrils; this is called a cere}^ Something somewhat 

 cere-like, but consisting of an enlarged and sicollen mem- 



