XXVITI 
BEAKS 
The beaks of birds are 'formed on the same lines 
as the horns of antelopes (see p. 266). There is a 
core, formed by prolongations of those bones known 
as the upper and the lower jaw, covered with a 
modification of skin known as horn; this outer 
covering, or sheath, is as insensitive as the horn- 
sheath of a buffalo, goat, sheep, or antelope. The 
base of the sheath (known as the cere) softens where 
it becomes continuous with the feather-covered skin 
on the bird’s head. 
The beaks of birds are used for offensive and defensive 
purposes : also for constructing nests, but above all 
things for obtaining food, and for this purpose it is 
often strangely modifiedo Long thin beaks are useful 
for obtaining worms from soft mud ; and long, strong 
and sharp beaks are used by herons and darters to 
secure slippery creatures like fish. Beaks which are 
short, but strong and sharp, enable many birds to 
extract the kernels of nuts, or grubs from the trunks 
and branches of trees. By means of powerful, sharp, 
and hooked beaks, birds of prey are able to rend the 
carcases of animals ; ducks, by means of flat, spatulate 
bills, sift mud and ooze to obtain the organisms 
necessary for their sustenance ; with their stout beaks 
open-bills can break the shells of molluscs and extract 
the soft animal within. 
z 
