OSTEOLOGY OF BIRDS 1 29 



Os prominens present over the wrist. In the shoulder girdle the 

 os furcula develops a shoulder upon the external aspect of either 

 clavicular limb for articulation with the coracoid. In the toes there 

 is an abbreviation of the basal joints of the second and fourth digit, 

 but not of the third digit, which last may show only a shortening of 

 the phalanx next beyond the basal one. 



1 Circinac Osseous septum narium not completed superiorly op- 

 posite the external nostrils; supraorbital portion of a lacrymal some- 

 what reduced, rounded at extremity and " accessory piece " small. 

 Hinder border of either aural cavity somewhat laterally expanded 

 above, posterior to the socket for the mastoidal head of the quad- 

 rate. Rudimentary basipterygoid processes present. Posteroex- 

 ternal angles of the postpalatines rounded. Usually seven facets 

 upon either costal border of sternum. Tarsometatarsus consider- 

 ably longer than the long diameter of skull, its hypotarsus repre- 

 sented by two small processes, with a rather wide valley between 

 them. Basal joints of second and fourth digits of pes abbreviated, 

 especially first mentioned one. In the third toe the phalanx next 

 beyond the basal one short; equals only half the length of the basal 

 one (Circus h udsonius). 



2 Accipitrinae. Supraoccipital portion of a lacrymal considerably 

 produced with the accessory piece at its extremity rather small. 

 Osseous nasal septum complete. Rudimentary basipterpgoid pro- 

 cesses present. (A ccipiter velox has general form of skull 

 as in Circus, but is small.) Subvertical part of maxillopalatine 

 platelike, not spongy. Body of sternum long, the extreme length of 

 its carina equaling the length of the femur. Its manubrium con- 

 spicuous and pointed ; the coraeoidal grooves do not decussate. 

 Tarsometatarsus much as in Circus, but the phalanx next beyond 

 the basal one of the third toe (mid anterior) not abbreviated. 



3 Buteoninae. Skull broad, very moderately compressed in vertical 

 direction. Descending limb of a lacrymal may or may not be in 

 contact with pars plana, but never fuses with it. The supraoccipital 

 portion of the bone large, broad, squarely truncated at the extremity 

 where it supports a free accessory piece, which is broader than this 

 end of the lacrymal itself. Rhinal portions of the maxillopalatines 

 often lofty, always more or less spongy, and fuse with the osseous 

 septum narium. 



Hinder margins of the postpalatines of the palatines squared 

 across transversely (not rounded). Basipterygoidal processes com- 

 monly present. Hvpocleidium of os furcula present though small. 



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