oo Lucas o« ///t- Os P)-o))iiiic)is. 



It is absent in Polyborns t/iarus, ^lilvago chunango. and the 

 following peculiar forms which were examined to see if thev 

 would throw any light upon the subject : Nyctibius, Strigops. 

 jVestor^ Megapodiiis^ Ocvdromus^ and Atagen. Neither was 

 an}' trace of it to be found in two specimens of Pandioii haliiv- 

 etiisixoxw N. Africa and the Duke of York group. Dr. Shufeldt's 

 theory that the os prominens is for the purpose of extending 

 the wing area struck me, as it did Mr. Jeffries, as being untena- 

 ble, from the fact that the increase of surface thus obtained was 

 too slight to be of any value.* 



The first proposition of Mr. Jefiries' summary is that the bone 

 serves to keep the friction of the extensor patagii longus from the 

 carpus. Were this the case it ought surely to be present in the 

 Albatross and Gull, birds which in a fresh breeze are continually 

 flexing and extending their wings according to the direction of their 

 flight and the var3-ihg force of the wind. But in both these birds the 

 OS prominens is absent, f and moreover, as we see in the Owls, it 

 may be so situated as not to prevent the friction of the ulnar por- 

 tion of the tendon. Second, that it serves onlv to a limited extent 

 to increase the power of the extensor patagii longus to abduct the 

 thumb, is shown by the tact that in the majority of cases that ten- 

 don is inserted in the first metacarpal. The exceptions to this, 

 so far observed by me. are in Otogyps calvus and Haliccetits al- 

 bicilla, where there is a strong tendon running from the os prom- 

 inens to the first phalanx of the thumb. The third proposition 

 has already been considered, and the fourth (that it protects the 

 carpus) must be rejected, both for the reason given by "Sir. Jctlrics. 

 and because as we see it in Owls it frequentlv does not lie over the 

 carpus at all. Only in Otogyps calvris does the os prominens seem 

 to exist as a simple sesamoid, and in that l^rd it is imbedded in 

 the tendon of the extensor patagii longus. and glides over the 

 scapho-hmar. Were I to venture a suggestion it would be that 



*The English Sparrow, which is but an indifferent flyer, can be deprived of one-half 

 of the secondaries and one-fourth of the primaries of both wings, in the long axis of 

 the pinion, without apparently impairing its flight. See Pettigrew. 



1 1 find that this statement must be modified in regard to Gulls, if not retracted alto- 

 gether, for since this paper was written I have found the os prominens in Larus glaucus 

 and /,. domhiicanus. It is present as a small, elongated, trihedral prism, imbedded 

 in the tendon of the extensor patagii longus, and playing over the flattened surface of 

 the scapho-lunar. 



