528 



STRUCTUEE AND CLASSIFICATION OF BIRDS 



■dinosaurian ; but the tinamous are like Apteryx in this. 

 The complete procoracoid of Struthio seems to be an archaic 

 character, as do the two free centralia in the foot of Apteryx. 

 As to negative characters, the most important of those that 

 are possibly, but not certainly, to be regarded as primitive 

 appears to be the usual absence of the oil gland. 



The long rectum of Struthio is probably an ancient 

 character ; but whether the absence of a bird-like syrinx in 

 all ratites except Bhea is a similar feature seems to be 

 doubtful. The large size of the blood corpuscles in the 

 ratites is noteworthy in this connection. 



The following table gives the principal characters of the 

 existing genera. From it may be inferred the somewhat 

 less modified condition of Apteryx and the very isolated 

 position of Struthio among the members of the group : — 



