3O THE CLASSIFICATION OF BIRDS 



nathous, though there is much ossification of the nasal septum. 

 Basipterygoid processes are always present in the Striges, and 

 always absent in the Psittaci ; but in the Accipitres they are only 

 present in the Gypoyeranidaz. 



The Falconiformes consist of three sharply defined Suborders, 

 which are supposed by some writers to be more nearly related to 

 other suborders than they are to each other : 



Psittaci. Feet zygodactyle; dorsal vertebras opisthocoslous ; 

 casca absent ; oil-gland tufted or absent. 



Accipitres. Feet normal or nearly so ; dorsal vertebrae hetero- 

 coelous; caeca rudimentary ; oil-gland tufted. 



Striges. Feet more or less zygodactyle ; dorsal vertebrae hetero- 

 coalous ; caeca large ; oil-gland nude.* 



5. PSITTACI. 



The association of the aquincubital Psittaci with the quin- 

 cubital Cuculi appears to me to be most objectionable. The 

 Psittaci agree with the Accipitres in their pterylosis much nearer 

 than with the Cuculi. The Psittaci and the Accipitres both possess 

 a cere, which is wanting in the Cuculi. On the other hand, the 

 Psittaci agree with the Cuculi in having the fourth digit directed 

 backwards. 



* The condition of the oil-gland, though occasionally useful in the diagnosis 

 of minor groups, does not appear to have much taxonomic value. Some birds 

 have no oil-gland, principally birds living in dusty localities, where it is of im- 

 portance that the plumage should be dry. None of the Struthioniformes have 

 an oil-gland. It is also wanting in the Otididce, in a few American Psittacidce, a 

 few genera of Co'umbidce, in the genus Argus amongst the Phasianidce, and in 

 the Podargidce. 



When present, the oil-gland may be either naked or surrounded by a tuft of 

 feathers. The tuft is obviously intended to protect the oil-gland from water, 

 and is chiefly confined to aquatic or semi-aquatic birds. 



No web-footed bird has a nude oil-gland. None of the Sphaenisci formes or 

 Ciconiiformes have a nude oil-gland. In the Falconiformes, the Striyidce alone 

 have a nude oil-gland. None of the Ralliformes have a nude oil-gland. In the 

 Charadriiformes, the Cdumbida and the Pteroclidce alone have a nude oil-gland. 

 The Cathartiformes have a nude oil-gland. Of the Coraciiformes, about half the 

 families have a nude oil-gland : CaprimuLgidce, Steatornithidce, Cypselidce, Coraciidce, 

 Meropidce, Trogonidce ; and in two of the families, Momotidce and Galbulidce, the 

 oil-gland, is nude in some species and tufted in others. In the Cuculiformes, the' 

 Cuculidai have a nude oil-gland. All the Passeriformes have a nude oil-gland. 

 In the Turniciformes the Eurypyga: have a nude oil-gland, and in the Galliformes 

 the Cariamidce. 



