THE CLASSIFICATION OF BIRDS 39 



young at birth throws no light on the question. The Pseudo- 

 gryphi are aquincubital, but so are the Ciconiiformes and the 

 Falconiformes, and some of the Coraciiformes. The Pseudo- 

 gryphi have median basipterygoid processes, but these occur also 

 in the Palamedeidcc among the Ciconiiformes ; in the Fvffinidce, 

 Gypogcranidce, and Strigidce amongst the Falconiformes ; and in 

 the CaprimulgidcK, Steatornithidm, and Trogonidce amongst the 

 Coraciiformes. The Pseudogryphi have an ambiens muscle; no 

 other species of Coraciomorphae has, but it is not surprising that 

 an Order of the Coraciomorpha3 should have become terrestrial in 

 its habits at a date early enough to retain the ambiens muscle. 

 The Pseudo- Vultures have a naked oil-gland, but in the Ciconii- 

 formes it is always tufted, and in the Falconiformes it is tufted in 

 the Tubinares and Accipitres, tufted or absent in the Psittaci, and 

 naked only in the Striges. In the Coraciiformes it may be naked, 

 tufted, or absent. In their pterylosis the Pseudo- Vultures agree 

 with the Ciconiiformes, and differ from the Falconiformes, in not 

 having the spinal feather- tract well defined on the neck ; but this 

 character is probably a primitive one which has been independently 

 retained by the Pseudo- Vultures, as it appears to have been by 

 the Bucerotidce in the Picarias, the Pygopodes in the Ralliformes, 

 &c. The small and elevated hallux of the Pseudo- Vultures is 

 certainly unique in the Coraciomorphge, but is found in some of 

 the Ciconiiformes and Falconiformes. The well-developed hallux 

 on the same plane as the other digits is essentially an arboreal 

 character, and was doubtless a primitive one which has been inde- 

 pendently lost by various families which have become more or less 

 terrestrial. The deep plantar tendons are so nearly Coraciiform 

 that the balance of evidence appears to be in favour of regarding 

 the Pseudo- Vultures as a very early offshoot of the Coraciomorphse, 

 and the one which has departed widest from the typical form. 



The Cathartiformes differ from the Coraciiformes in many 

 important particulars : 



They have an ambiens muscle. 



The hallux is elevated above the plane of the other digits. 



The nostrils are pervious. 



.The young are covered with a much denser covering of down 

 before the feathers appear. 



The adults retain some down both on the feather-tracts and 

 on the bare spaces. 



Amongst the Coraciomorph.se the Cathartidce are the only 



