494 STRUCTURE AND CLASSIFICATION OF BIRDS 



are fused) are set aside as comparatively valueless as marks of 

 near relationship, there remain enough anatomical resem- 

 blances to justify the older view that all these birds are but 

 members of one and the same group. FUEBKINGEK has 

 denied this in his ' Untersuchungen,' and places Apteryx, 

 together with the Dinornithidse, apart from the other stru- 

 thious birds, and has again separated Struthiiformes from 

 Eheiformes and Casuariiformes, deriving all from different 

 levels of the ornithic tree. There is no doubt that the 

 various types of struthious birds do require separating into 

 at least six families ; but the likenesses among them appear 

 to me to forbid any wider separation. The close resemblance 

 of the palate throughout the group, so far as we know it 

 (JEpyornis is not known), is a strong reason for associating 

 them together ; perhaps even the osteological and other 

 characters, which, as already suggested, are but evidence of 

 the loss of the flight power, may be of more importance as 

 an argument for affinity than is generally admitted ; it may 

 show that they are allied, because the degeneration has pro- 

 ceeded along the same lines. There is, it is true, not a great 

 deal of evidence in favour of this view ; but we have the 

 penguins also with a degenerate wing, in which the modifi- 

 cations of structure ' have progressed along different paths. 

 They have, for example, lost the biceps, which is present in 

 all Struthiones, while the feathers of the wing are equally 

 inefficient as aids to flight with those of the Struthiones, but 

 are quite unlike them. The peculiar muscle of the thigh, 

 which will be found described as an adjunct of the accessory 

 femorocaudal, is one of those apparently small facts of struc- 

 ture which, on account of their very minuteness, seem of 

 importance as a mark of true relationship. 



The fact that all of the struthioris birds have large or 

 moderately developed caeca is further evidence of affinity. 

 It might be thought that the usual absence of the oil gland 

 was one of those characters affording clear evidence of degene- 

 ration ; but its capricious appearance and disappearance in 



1 See, however, the qualifying remarks with regard to the wings of Apteryx 

 on p. 499. 



