BEAKS. 



189 



form and thickness according to the habits of the species. In the 

 genus Falco the bill is shorter than the head ; the upper mandible 

 is furnished at the base with a bare coloured skin, of a peculiar 

 dense texture, called the cere ; its outline slightly conyex as far 

 as the edge of the cere (Fig. 61), then curved so as to form about 



Fig. 61. 



the third of a circle, and evidently destined, in connection with its 

 formidable claws, to tear its prey. 



In the Toucans Eamphastid^ the bill is half a foot long, 

 hollow within, thin, and nearly transparent ; and the mandibles 

 are so disposed as to combine, with their great bulk, strength 

 and lightness, and assisting by their digestive power to assimilate 

 both animal and vegetable food (Fig. 62). In the Pelicanidje, 



Fig. 6a. 



as in the Common Cormorant, Phalacrocorax carbo, the bill is 

 long, straight, and compound; the upper mandible curved 

 towards the point, the lower compressed ; the base inserted in a 

 email membrane which extends under the throat. In the back 

 part of the head is an additional bone (Fig. 63, a), attached in 



Fig. 63. 



such a manner to the occiput as to admit of great expansion, which 

 permits of its swallowing plaice and other flat fish of considerable 



