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ON THE TRAIL OF AN EXTINCT BIRD. 



By C. W. De Vis, M.A., Corr. Mem. 



The function of the wing in birds is in kind almost uniform, 

 though, in exercise it varies greatly. It is therefore probable 

 that any variation observable in the form or relative dimensions 

 of a constituent bone of the wing (the ulna, for example) has been 

 brought about solely by the habitudes of the bird, or those of its 

 ancestors, in the use of the power of flight. The extent of the 

 variation so produced will be comparatively limited : inconspicuous, 

 indeed, by the side of the results of diverse adaptation acting on 

 the corresponding segment of the mammalian fore-limb. We are 

 thus prepared to find the ulna maintaining in birds a general 

 sameness of character. If we compare it with the humerus its 

 uniformity is but accentuated: and naturally so since its surface is 

 less subjected to the moulding agency of muscular origin and 

 insertion than is that of the proximal segment of the lever, the 

 recipient of the muscles moving the whole, and the purveyor of 

 others which give motion to the distal segments. These con- 

 siderations may serve to account for the fact that the differentia- 

 tions of the ulna have been found too insignificant to be discussed 

 by comparative osteology ; and undoubtedly the bone is not that 

 part of the bird's skeleton which throws most light on its general 

 economy, yet it may be that it is not altogether impossible to find 

 in the fossil ulna of a bird some guidance to the systematic place 

 which should be assigned to the organization of which it formed a 

 part. In the following attempt to do so the characters which have 

 appeared to be available are the proportions of the bone discovered 

 in its relative length and thickness, its curvature, the number, size 

 and disposition of the tubercles corresponding to the secondary 

 remiges, the shape of the shaft at its distal end, and the conforma- 

 tion of the articulating surfaces and parts adjacent to them. 



