THE CLASSIFICATION OF BIRDS 165 



ArchcBopteryx has the smallest number of cervical vertebrae 

 of any bird (ten), a fact which recalls the nine .vertebrae or so 

 of the cervical region of lizards and crocodiles. Now, among 

 other recent birds there are none which have a smaller 

 number than that possessed by certain passerines. Fifteen 

 is perhaps the average number of these vertebrae among 

 birds ; but among passerines the low number of thirteen is 

 to be met with. Nearly all the Anomalogonatse are holorhinal, 

 as was the Archceopteryx. It is doubtful, however, whether 

 this particular fact advances my argument, as there are 

 reasons (see p. 144) for considering the schizorhinal arrange- 

 ment to be the (dder, and for looking upon the holorhinal as 

 a derivative. 



There remains for consideration the large assemblage of 

 birds which, taken together, correspond to the Homalogonatse 

 of Gaekod. In a preliminary way we may regard, as I 

 have pointed out above, four characters at any rate as 

 primitive. 



These are the presence of basipterygoid processes, the 

 possession of two carotid arteries and of the fifth cubital 

 remex, and the simplicity of the intestinal coils. The only 

 birds which have all of these are certain Galli and certain 

 Turnices. Allowing for the degeneration of the wing, the 

 struthious birds may be referred to a nearly equally low 

 place in the system. In many groups, however, we find a 

 near approximation to this presumably primitive condition. 

 Thus among the anserine birds Palamedea is deficient only 

 in the fifth remex. Among ' G-rallse ' it is only the same 

 character that is wanting in certain forms to complete the 

 four requisite characters. And some of them — e.g. Cariama, 

 Psophia — have this elsewhere missing feather, though those 

 particular forms have not some of the other characters. 

 Opisthocomus, the cuckoos, and Musophagidae are not far 

 off from the base of the series, while the trogons, if they 

 had both carotids, would be among the (hypothetically) 

 lowest groups. The facts in question may be thus tabu- 

 lated : — 



