AVES. 



313 



of the mandibles are bent downwards abruptly 

 (Jig. 148), have all transverse horny lamina; 



Fig. 148. 



which are nearly allied to the Anat'ulee, the la- 

 teral laminae are developed into small conical 

 tooth-like processes, which serve to hold fast 

 the fishes, which the Goosander destroys in 

 great numbers. 



Fig. 149. 



Bill of the Flamingo. 



arranged along their edges, which, when the 

 bird lias seized any object in the water, serve, 

 like the whalebone laminae of the Whale, to give 

 passage to the superfluous fluid. The aquatic 

 habits of all these birds are in harmony with 

 this structure. In the Goosanders (Mergus), 



Bill of the Goosander. 



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, without 

 which the equilibrium necessary for flight 

 would have been destroyed. The singularity 

 of the structure of these bills demands a more 

 particular consideration. 



The osseous portions of the mandibles of 

 the Toucan (fig. 150) are adapted to cora- 



Fig. 150. 



Bitt of the Toucan. 



bine, with great bulk, a due degree of 

 strength and remarkable lightness, and their 

 structure is consequently of a most beautiful 

 and delicate kind. 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 considerable 

 resistance if the force be increased for the pur- 

 pose of crushing the beak. At the points of 

 the mandibles the outer walls are nearly a line 

 in thickness ; at other parts in the upper beak 



case. In the specimen which we dissected (see 

 Proceedings of the Zoological Society, Part ii. 

 p. 141) the upper mandible was so firmly fixed to 

 the cranium as only to be moved with that part, 

 while the lower mandible was freely moveable 

 when the head was fixed. The Flamingo is remark- 

 able for applying the upper mandible to the soil, 

 which it shovels backwards in searching for its 

 food. 



they are much thinner, varying from one- 

 thirtieth to one-fiftieth part of an inch, and in 

 the lower beak are from one-twentieth to one- 

 thirtieth of an inch in thickness. 



On making a longitudinal section of the upper 

 mandible (a,jig. 150) in the Rhamphastos Touco, 

 its base is seen to include a conical cavity about 

 two inches in length and one inch in diameter, 

 with the apex directed forwards. The walls of 

 this cone consist of a most beautiful osseous 

 net-work, 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 imme- 

 diately support the latter being almost invariably 

 at right angles to the part in which they are in- 

 serted. The whole of the mandible anterior to 

 the cone is occupied with a similar net-work, the 

 meshes of which are largest in the centre of 



