16 CLASSIFICATION OF BIRDS. 
Suborder 11. ACCIPITRES. 
The Birds of Prey, after the Owls (Striges), the American Vultures (Cathartes), and the 
Secretary Bird (Serpentarii) have been excluded, may be diagnosed as follows :— 
A. Young born helpless, but covered with down. B. Basipterygoid processes absent. 
C. Spinal feather-tract well defined on the neck. D. Hallux always present, and 
connected with the flewor longus hallucis, and not with the flecor perforans digitorum ; 
the two tendons bound together by a fibrous vinculum. 
A simpler, though much less satisfactory, diagnosis is as follows :— 
E. Myological formula A+. F. Dorsal vertebra heteroccelous. 
The first of these characters (which implies that the ambiens and femoro-caudal muscles 
are present, whilst the accessory femoro-caudal, semitendinosus, and accessory semitendinosus 
are absent) excludes all birds except the Fregatide (a family in the suborder Steganopodes), 
which are excluded by the second character. 



























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The vertebre of most birds are heteroccelous or saddle-shaped—that is to say, the facets, 
where they articulate with the adjoining vertebra, are convex in front and concave behind 
when seen in yertical section, but are concave in front and conyex behind when seen in 
lateral section. In a few birds, however, the dorsal vertebrae, especially the hinder ones, are 
more or less opisthoccelous—that is to say, the facets, where they articulate with the 
adjoining vertebrae, are either straight or concaye (not conyex) behind when seen in lateral 
section. 
This character breaks down in the Coracie and the Steganopodes, in both of which sub- 
orders families with opisthoccelous dorsal vertebre occur, together with others in which the 
dorsal yertebrie are heteroccelous. 

