544 



NATURAL HISTORY. 



on its upper surface a curious casque, or helmet, varying in shape and size 

 with the species. Though so large, this bill is very light, and is of a 

 regular honey-combed structure ; but this is much more marked in some 

 than in others. In the great hornbill it is very much heavier than in 

 others, and this bird beats the trees with its heavy hammer-fronted casque, 



Fig. 447. — Hornbill (Buceros bicornis). 



producing resounding thuds which can be heard long distances. Before 

 this hammering habit was actually known, Professor Flower was confident 

 that the head was used as a pounding organ, so peculiar is its structure. 

 The bone in the part that hammers is very thick, and from it proceeds a 

 layer of dense bone which passes above the cavity of the brain, so that the 

 strain comes on the neck, while the 1 train itself is out of the line of the 

 -hock. 



