200 Shufeldt on the Os Prominens in Hawks . 
ments, with the one exception already referred to, the limb being 
in a position of extreme extension. When the member is 
brought to the side in a position of rest, the ossicle no longer 
being held in its erect position by the stretched tendon of the 
extensor plicce alar is, falls forwards and inwards to cover the 
ulnar aspect of the carpal articulation and forms in so doing an 
unusually rotund joint, particularly noticeable in the bird before 
the removal of the elastic integuments that tend further to hold 
it in this position in the closed wing. 
As this little bone can in no way be considered as belonging to 
the bones of the carpus proper, I have named it the os pro?ninens , 
and regard it in the same light and place it in the same category 
with the os humero-scapulare of the shoulder joint of others of 
the class, they being simple segments super-added to the series 
of vertebrae, modified or otherwise, of the avian skeleton, to 
fulfil a certain purpose. 
The function of the os prominens can be studied, and its action 
thoroughly appreciated, by an examination of the wing in any 
of the Hawks where it is found ; a very recently killed specimen 
being the best subject. 
With the wing closed, it simply falls into the position that I 
have already endeavored to describe, and in doing so, it acts 
more as an additional protection to the anterior aspect of the 
carpal articulation than anything else — by no means an unim- 
portant object among the Falconidce ; in the extended limb, where 
it becomes erect, and the elastic tendon of the extensor plicce 
alaris is put on the stretch, we will at once observe that the 
surface of the integumental membrane, that is found in the tri- 
angular space between shoulder and carpus, is very much greater 
than if that tendon were simply inserted at the wrist-joint ; this 
circumstance giving to these Raptorial birds a more extensive 
alar superficies, a very important auxilliary during their sustained 
flight aloft when, sailing in circles, they scan the earth below for 
their food. 
The various bones in the cut are lettered to correspond with 
the same bones of my former published monographs, and the os 
prominens is here lettered os. p., and will be invariably so desig- 
nated in future plates and papers when it becomes necessary to 
refer to it. I have thus far failed to discover this osteological 
character in any of the class except the Falconidce, and doubt 
