io8 



NEW YORK STATE MUSEUM 



Except in point of size there seem to be no very decided differ- 

 ences (between the skeleton of Polyborus cheriway and 

 P o 1 y b ol- us lutosus — they are very trivial to say the least. 

 This being the case I will make the skeleton of Polyborus 

 lutosus stand duty here for what we have to say about the 

 osteology of these birds, and briefly refer to any exceptions met 

 with in the other form. 



Rather massive in its general proportions, the superior osseous 

 mandible is deep in the vertical direction ; very moderately com- 

 pressed transversely throughout 

 (more so in Polyborus c h e r i - 

 ,w a y ) ; souiewhat feebly hooked at 

 ,the apex, and without the tomial 

 notches as in Falco ; and with the 

 medio-longitudinal crest at the fore- 

 part of the buccal aspect strongly de- 

 veloped. The tomial margins are 

 cultrate and moderately produced 

 downward all the way round. Either 

 narial aperture is comparatively 

 small, reniform in outline, being 

 placed semivertically, with the top 

 most posteriorly situated. Through 

 the opening the aUnasal tuybinal may 

 l)e plainly seen as in Falco. Each 

 nasal bone is completely fused with 

 the surrounding osseous structures, 

 and shows a small foraminal perfora- 

 tion near its center. The lateral 

 longitudinal sutural lines of the nasal 

 processes of the premaxillary are 

 persistent throughout life. Super- 

 iorly, the frontal region is flat and 

 wide between the orbital margins ; more posteriorly the parietal 

 eminences are rounded and smooth, giving good evidence of a fair- 

 S'zed brain case, which in reality this species possesses. 



Regarded upon its lateral aspect, we are to note that the aural 

 aperture is large ; the postfrontal process rather small and directed 

 downward,^ while the squamosal apophysis is double, an obliquely 



Fig. 53 Suptriin- view of the skull 

 of Polyborus cheriway. 

 Natural size 



''■ It is rather a curious thing that in this specimen the left postfrontal process has 

 had its npical jiart formed from a separate ossific center ; and the sutural traces 

 are still easily to be perceived. • 



