THE CLASSIFICATION OF BIEDS 37 



absent in the Columbae), but in the LimicolsB it is tufted. The 

 Limicolse have some down distributed all over the surface in the 

 adult: in the Pterocles it is restricted to the feather-tracts, anl 

 in the Columbse it is absent altogether. The nostrils are pervious 

 in the Limicolje, bat impervious in the Pterocles and the Columbse. 

 On the other hand, the Pterocles differ from both the allied sub- 

 orders in having the plumage of the neck almost continuous. 



The Pterocles are confined to the Old World, and to the tropic 

 and subtropic parts of it. 



15. COLU.MB.-E. 



The systematic position of the Pigeons has been a puzzle to 

 ornithologists. They appear to be a very isolated group of birds, 

 and widely different opinions as to their affinities have been 

 expressed. Linnaeus regarded the conditions of the newly hatched 

 young and the development of the hallux as very important 

 characters, and placed the Pigeons in his Order PASSEEES. Pen- 

 nant established an Order of Columbine Birds, which he placed be- 

 tween his Gallinaceous Birds and his Passerine Birds. Cuvier went 

 a step further and included the Pigeons in his GALLINACES. Now 

 that it has been established that the Pigeons are aquincubital, 

 whilst both the Gallinaceous and Passerine Birds are quincubital, 

 it seems most improbable that any of these opinions can be true. 

 If the choice be restricted to the aquincubital birds with normal 

 plantars, the Pigeons seem to fall naturally into the schizogna- 

 thous schizorhinal Order, and represent the tree-perching con- 

 tingent of the Charadriiformes. 



The ColumbaB may be regarded as almost cosmopolitan ; they 

 are only absent from the Arctic and Antarctic Regions. 



CORACIOMORPH^:. 



The Coraciomorphso may be regarded as a central group of 

 families which are easily diagnosed by their abnormal deep 

 plantar tendons. Most unaccountably they contain four aquin- 

 cubital families, two families which appear to contain both quin- 

 cubital and aquincubital species, whilst the rest of the families 

 are all quincubital. 



The Coraciomorpha? may therefore be looked upon as a middle 



