AVES. 223 
Each of these orders is subdivided into families and genera, 
and principally from the conformation of the beak. But these 
different groups frequently pass into each other by almost 
imperceptible gradations, so that there is no other class in 
which the genera and sub-genera are so difficult to limit. 
ORDER I. 
ACCIPITRES, Lin. 
Birds of prey are known by their hooked beak and talons, 
powerful weapons, with which they pursue other birds, and 
even the weaker quadrupeds and reptiles. They are among 
Birds what the Carnivora are among Quadrupeds. The 
muscles of their thighs and legs indicate the strength of their 
claws ; their tarsi are rarely elongated; they have, all, four 
toes; the nail of the thumb and that of the internal toe are 
the strongest. 
They form two families, the diurnal and the nocturnal. 
The eyes of the diurnal Birds of prey are directed sideways ; 
they have a membrane called the cera, covering the base of 
the beak, in which the nostrils are pierced ; three toes before, 
one behind, without feathers, the two external ones almost 
always united at base by a short membrane; the plumage 
dense, the quills strong, and great power onthe wing. ‘Their 
stomach is nearly altogether membranous, their intestines of 
but small extent, their cecum very short, their sternum broad 
and completely ossified in order to give more extended attach- 
ments to the muscles of the wings, and their fourchette semi- 
-eircular and widely separated, the better to resist the violent 
flexions of the humerus necessary to a rapid flight. 
Linnzus comprehended them all under two genera, which 
are so many natural divisions, the Vultures and the Falcons. 
Vor. I.—2 D 
