12 
ON THE CLASSIFICATION OP BIRDS. 
probable that the three last — which constitute the aber- 
rant group of the class — are only of the rank of tribes ; 
equivalent to the Fissirostres, Scansores, &c. hereafter 
noticed. As the circularity of these three groups^ taken 
collectively, has not yet been made out, we shall there- 
fore, for the present, consider tliem as holding the rank 
of orders. The typical circle is seen in the order Inses- 
SORES, and the subtypical in that of the Raptores. 
Groups, truly natural, may be defined by more than 
one set of characters ; hence it is, that, independent of 
every other, the primary divisions of this class may be 
shortly and beautifully discriminated by their feet. In 
these members we have three striking modifications of 
structure {fig. 2.). In the Raptores, or birds of prey 
the feet (n) are raptorial ; that is, adapted for seizing and 
destroying other animals ; the claws are consequently 
sharp, much hooked, and retractile, and they may be em- 
ployed both offensively and defensively. In the second, 
or pre-eminent type — the Insessores — the feet are 
constructed more especially for grasping or perching (6) ; 
the claws are comparatively small, less curved, and are 
not retractile ; while the hind toe, as in the last, is 
placed upon the same level as the fore toes. In the third, 
or aberrant division, composed of the fowls (c), the 
waders (d), and the swimmers (e), none of the above 
characters are found. The hind toe, when it exists, is 
always elevated above the plane of the others, and the fore 
toes are more or less connected by a membrane. The 
