196 BRITISH BIRDS. 
Family PASSERID, or SINGING BIRDS. 
The Singing Birds, together with three other families* (of which there 
are no representatives in Europe), constitute what are frequently called 
the true Passeres, the great central group of dominant birds—by far the 
most numerous in genera and species, yet exhibiting few anatomical 
differences inter se—the most highly developed, and yet at the same time 
the most cosmopolitan of birds. They may indeed be said to be absolutely 
cosmopolitan, being found throughout the world, except on such rocky 
coasts where no bird can exist which does not obtain its food from the 
water. 
The Passeres are the typical birds, the great central apex of the genea- 
logical tree, very nearly related to each other, and surrounded by outlying 
families or. branches much more distantly related, and consequently pre- 
senting important anatomical characters by which to separate them from 
the great central group and from each other. 
The Passeres are the true Aves; the other families are the failures, the 
least developed descendants of the intermediate forms which once connected 
Birds and Reptiles, families containing comparatively few genera and 
species, some fast dying out, but so widely separated from each other that 
to trace their relationship we should have to go back almost to the roots 
of the genealogical tree. So obscure indeed is this connexion that orni- 
thologists cannot decide in some cases (the so-called Ratite, for imstance) 
whether they form one family or great group, or are the remnants of 
several distantly connected groups. 
The Passeride are separated from the other three families to which 
they are most nearly allied by a peculiar structure of the singing-appa- 
ratus at the lower end of the windpipe; but this apparently exhausts 
the anatomical characters which our physiologists have been able to discover, 
and leaves us with nearly half the known species of birds so closely 
related to each other that no known internal characters exist by which 
they may be subdivided. 
* Sclater (Ibis, 1880, p. 345) divides his order Passeres into four suborders :—Oscines, 
comprising about 4550 species (nearly half the species of birds known), principally found 
in the Old World, but many peculiar to the New; Oligomyode, comprising about 550 
species, principally found in the New World, but some peculiar to the Old ; Zracheophone, 
comprising about 500 species confined to the New World; and Pseudoscines, comprising 
half a dozen species confined to Australia, 
