64 
ON THE CLASSIFICATION OF BIRDS. 
mouths, both which characters belong to the goatsuckers 
and the swallows : in both these the mandibles are so 
weak as to be only capable of clasping small insects ; 
and it is very questionable whether those of the ordinary 
Caprimulgida are ever employed for this purpose, the 
remarkable smallness of both mandibles rendering them 
little more than rudimentary. The great majority of 
birds which catch their food in the air have short bills. 
but of great breadth, as we see in the flycatchers ; while 
those birds which peck their food, like crows and thrushes, 
have them generally of a moderate length ; or, at least, 
they are never depressed, as this latter form always im- 
plies weakness, and an incapacity for striking the bill 
against any substance. The longest bills are found among 
the w'aders (GraUatores, fig. 31. ab), and such birds as 
plunge this member into substances which contain their 
food. The snipes, woodcocks, and many of the godivits, 
are familiar examples of this structure ; and they are 
well known to insert their bills to a considerable depth 
in soft mud, for the purpose of finding worms and 
aquatic insects. This great elongation of the bill, or 
mouth, as we have had frequent occasion to remark 
before, is one of the leading characters of the grallatorial 
type in its different modifications throughout the animal 
kingdom. We consequently find that the tenuirostral 
tribes, represented by the humming birds, have the long- 
est bills (/g.31 .c)among the perchers ; and the pigeons 
are so characterised by this very circumstance in the order 
of Rasores, although their bills, in comparison with 
those of the generality of birds, are only moderately long. 
