THE BODY. 
9 
or beak is unprovided with teeth, but the mandibles are, 
as we have before observed, covered with a horny sheath, 
the edges of which are sometimes sharp, sometimes 
blunt, and in some cases notched or serrated, in others 
smooth, and are either hard or soft according to the 
species. 
In flesh-, fish- and grain-eating birds this sheath is 
excessively hard, while among the insectivorous it is soft, 
and is especially so with those which extract insects from 
mud; in the latter case the bill often acts as a feeler. 
The tongue varies as much in its formation as the beak. 
In those birds which swallow large quantities of food at a 
time, like the Pelican and Stork, it is small and cartila¬ 
ginous ; with those feeding on fruit it serves as a taster, 
being large and fleshy, as in the Parrots; in the 
Sun- and Humming-birds it is provided with brush-like 
extremity, and can be projected like that of the Woodpecker. 
The gape is often surrounded with papillae and spines, 
and is sometimes of a large size; certain glands secrete 
the saliva. The gullet in some birds is of a uniform 
width throughout, and but slightly elastic; in others 
just the reverse. In the Lammergeir it is furnished 
with folds inside, so as to facilitate its extension. In 
others, again, namely, diurnal Raptores and granivorous 
birds, it is distinguished by a single or double pouch 
or bag of a round form, which we call “cropin this 
pouch all food is, in a certain degree, prepared for 
digestion by maceration and decomposition. During 
the breeding season the internal lining of the crop of 
some birds secretes a certain milky or cheese-like 
substance, which serves as the first nutriment of their 
young, as among Pigeons. When there exists a true 
crop the lower portion of the gullet is generally 
I 
c 
