DIGESTIVE SYSTEM OF BIRDS. 



149 



Bill of tlic Flamingo. 



of the Whale, to give passage to the superfluous fluid. The 

 aquatic habits of all these 

 birds are in harmony with 

 this structure. But the long- 

 legged palmiped sifts the sand 

 of the sea-shore by raking it 

 up with the bill reversed, as 

 shown in fio;. 14. In the 

 Goosanders {Mergiis,^g. 71), 

 the lateral laminae are de- 

 veloped into small conical 

 reflected tooth-like processes, 

 which serve to hold fast the 

 fishes on which they feed. 



The bills of the Toucans and Hornbills are remarkable for 

 their enormous size, which is sometimes equal to that of the 

 whole bird. The substance of the 

 beak in these cases is extremely 

 light and delicately cellular ; yet 

 the osseous portions are adapted 

 to combine, with great bulk, a 

 due degree of strength. The 

 external parietes are extremely 

 thin, especially in the upper beak : they are elastic, and yield 

 in a slight degree to moderate pressure, but present consider- 

 able resistance if the force be increased for the purpose of 

 crushing the beak : they gain thickness at the points of the man- 

 dibles. 



On making a longitudinal section of the upper mandible, 

 fig. 53, «, its base is seen to include a conical cavity about two 

 inches in length and one inch in diameter, with the apex directed 

 forward. The walls of this cone consist of an osseous network, 

 intercepting irregular angular spaces, varying in diameter from 

 half a line to two lines. From the parietes of the cone a net- 

 work of bony fibres is continued to the outer parietes of the 

 mandible, the fibres which immediately support the latter being 

 almost invariably at right angles to the part in which they are 

 inserted. The whole of the mandible anterior to the cone is 

 occupied with a similar network, the meshes of which are largest 

 in the centre of the beak, in consequence of the union which 

 takes place between different small fibres as they pass from the 

 cu'cumference inwards. The principle of the cylinder is intro- 

 duced into this structure : the smallest of the supporting pillars 



Bill of the Goosander. 



