200 Shufeldt on the Os Prom incus in Hawks. 



merits, 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 plica 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 hone can in no way be considered as belonging to 

 the bones of the carpus proper, I have named it the os prominens, 

 and regard it in the same light and place it in the same category 

 with the os hnmcro-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 plica 

 alar is 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 Falconida. and doubt 



