Shufeldt on the Os Prominens in Hawks. 1 99 
The usual long bones and carpal segments interested in the 
formation of the wrist joint of this Hawk held their positions 
and relations to each other as we find them described by ornithot- 
omists generally ; but superadded to these I found the ossicle which 
proved to be the counterpart of one of the pair I already had in 
my possession, found in the first specimen ; in form it resembles 
an irregular parallelopiped or rather, and more correctly speaking, 
the frustum of a four-sided pyramid, its distal face being concave 
and its summit more or less tuberous. Its altitude measures 6 
centimetres, while its base has a diameter of 3 centimeters, and 
is smooth, being covered with a thin layer of cartilage for articu- 
lation with a diminutive facet found on scapholunar and an exten- 
sion of the usual horizontally compressed, distal end of radius 
that was produced anconad for that special purpose. The articu- 
Right Carpus, Circus Hudsonius, Ulnar aspect. 
u, ulna, r, radius. c, cuneiform. s, scapho-lunar. os.p, os prominens. 
m, metacarpus. d, index digit. epa , tendon of extensor plicae alaris. 
lation is a true arthrodia, the little bone being perfectly free to 
glide over the surface in question, being restricted in its move- 
ments mainly by the ligaments that are attached to it and by the 
tendon of the extensor plicce alaris that is found to be inserted at 
its summit. The principal ligaments are found to be those that 
are attached about its base to hold it in the position it occupies, 
and are blended with the carpal ligaments, generally ; and an 
additional broad ligamentous expansion that is thrown out from 
the radial angle and aspect, from its summit to its base, to be 
inserted into the head of the metacarpus. 
My sketch of the carpus in Circus , accompanying this paper, 
represents the bones of a life, size from a large female of the 
species, entirely divested of all the engaged tendons and liga- 
