THE CLASSIFICATION OF BIRDS 43 



TBOGONIFORMES. 



19. TKOGONES. 



The arrangement not only of the deep plantar tendons in 

 the Trogons, but also of their digits, differs from that of any 

 other birds. The second digit is reversed, and the flexor longus 

 Jiallucis leads both to it and the hallux, leaving the flexor perforans 

 digitorum to lead to the third and fourth digits only. The Order 

 contains only one family (Trogonidce), and consequently only one 

 suborder (Trogones). 



The Trogonidce resemble the Caprimulgidce, the Steatorniihidce, 

 and the Cathartidce in having basipterygoid processes. They also 

 resemble the Caprimulgidce and the Picidce in being schizo- 

 gnathous. The pterylosis of the Trogons is typically Passerine, 

 in which respect the Trogonidce closely resemble the Alcedinidce. 

 Another Passerine character which they possess is the nude oil- 

 gland a peculiarity also found in the Galbulidcv, the Cypselidce, 

 the Gaprimulgidce, the Steatornithidce, the Coraciidce, the Meropidce, 

 the Cathartidce, and some of the Momotidce. 



The geographical distribution of the Trogonidce is very remark- 

 able. It is strictly confined to the Tropics : nevertheless it is not 

 confined to tropical America, but extends also to tropical Africa 

 and India an instance of a discontinuous area of distribution not 

 easy to explain except on the assumption that the family is a very 

 old one. 



PICIFORMES. 



20. SCANSOEES. 



The Piciformes are a very sharply defined group, which may 

 easily be diagnosed, irrespective of the deep plantar tendons. 

 They have zygodactyle feet ; the spinal feather-tract is well 

 defined on the neck and upper back by lateral bare tracts, and 

 is forked on the lower back ; and they have no basipterygoid 

 processes. 



The families contained in this Order may be reduced to four : 

 The Picidce are schizognathous ; the Capitonidcc (including the 

 Indicatorince) are segithognathous ; the Galbulidce (including the 

 Bucconince) and the Rhampliastidcc are desmognathous, the former 



