iS Field Museum of Natural History — Zoology, Vol. IX. 



2. Hypognathous. Lower mandible longer than upper man- 

 dible. (Example: Black Skimmers, Rhynchops.) 



3. Paragnathous. Both mandibles of about equal length. 



4. Metagnathous. Mandibles crossed. (Example: Crossbill, 

 Loxia. ) 



The shape and size of the bill vary greatly, as will be seen by the 

 following illustrations representing fifteen of the principal types 

 among our birds: — 



PiMirostml bill of WMppoormll 



Tenuirostral bill of llnmming-bxni 



Dent!ro«tral Bill of Shrilct 



Conimalral bill of Song Sparrow 0,ltrin.slral bUl of Lea.'<l BUtrm 



LaviellirostraJ bill of Duck 



Bill of Woodpecker 



Cere. A membrane (usually hard ) , which covers the base of the 

 upper mandible. (Hawks, Parrots, Jaegers. ) 



Nasal Fossa, or Nasal Groove. Groove in which the nostrils open. 



Gonys. Bend of lower mandible; usually used to include the 

 outline of the under mandible, from the angle to the tip. 



Culmen. The ridge of the upper mandible. 



