14 GENERAL DEFINITIONS. 



ters of the bill, feet, wings and tail, with which de- 

 scriptive ornithology is so largely occupied. 



The Bill. Whatever its shape, this part of a bird 

 always consists of an upper and an under mandible, 

 these being its bony framework, covered with horny 

 or leathery integument. Some birds of early periods 

 had true teeth, like most reptiles and mammals, but 

 such is not the case with any birds now living ; the 

 hardness of the bill answering every purpose of 

 teeth. The principal parts of the bill are illus- 

 trated in Fig. 2. In most birds the covering of the 



FIG. 2. PARTS OF A BILL. <z, side of upper mandible; , oilmen; c, nasal fossa : ^nos- 

 tril ; e (see below) ; f-, gape, or whole commissural line ; g t rictus : k, coinmissural 

 point or angle of the mouth ; /, ramus of under jaw ; /, tomia of under mandible (the 

 reference line e should have been drawn to indicate the corresponding tomia of the 

 upper mandible) ; k, angle of gonys ; /, gonys ; tn, side of under mandible ; , tips of 

 mandibles. 



bill is entire ; in some, as in the Petrel, it is pieced. 

 Birds of prey and some others have a soft swollen cov- 

 ering of the base of the upper mandible, called the 

 cere ; and in such the tip of this mandible is hooked 

 over that of the lower mandible. The upper outline 

 of the bill is the culmen, the corresponding lower out- 

 line is the gonys, the line of meeting of the two man- 

 dibles is the commissure. The nostrils open usually 

 at the base of the upper mandible, and commonly in a 



