88 
Lucas on the Os Prominens. 
It is absent in Polyborus tharus , Milvago chimango , and the 
following peculiar forms which were examined to see if they 
would throw any light upon the subject : Nyctibius , Strigops , 
Nestor , Megapodius , Ocydromus , and Atagen. Neither was 
any trace of it to be found in two specimens of Pandion halice- 
etus from 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. Jeffries’ 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 varying force of the wind. But in both these birds the 
os prominens is absent, j* 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 only to a limited extent 
to increase the power of the extensor patagii longus to abduct the 
thumb, is shown by the fact 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 Haliceetus 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 Mr. Jeffries, 
and because as we see it in Owls it frequently does not lie over the 
carpus at all. Only in Otogyps calvus does the os prominens seem 
to exist as a simple sesamoid, and in that bird it is imbedded in 
the tendon of the extensor patagii longus, and glides over the 
scapho-lunar. 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 glaums 
and L. dominicanus. 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. 
