Shufeldt oji the Os Prominens in Hazvks. 



199 



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 scapJiohinar and an exten- 

 sion of the usual horizontally compressed, distal end of radius 

 that was produced anconad for that special purpose. The articu- 



rpa 



Right Carpus, Circus Hndsonius, Ulnar aspect. 

 11, ulna. r, radius. c, cuneiform. s, scapho-lunar. os.p, os prominens. 

 m. metacarpus. J, index digit. epa, tendon of extensor plica? 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 exte?isor filicce. 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- 



