IOO NEW YORK STATE MUSEUM 



d a t u s next to Haliaetus. I have examined the National 

 Museum skeleton [no. 17836]. It is not especially near Haliae- 

 tus 1 e u c o cl e p h a 1 u s . The two "birds have very different 

 sterna [see pi. 11]. 



From the osteology of the accipitrine .birds which we have thus 

 far studied in the present treatise, we pass to the true falcons, the 

 caracaras, and the Osprey, a glance at the skeleton of any one of 

 these being sufficient to convince us that we are confronted with a 

 group of raptorial birds possessing very different osteological char- 

 acters as compared with the buteonine types heretofore noticed. 

 More careful consideration of them convinces us that they are sus- 

 ceptible of perhaps something more than generic division ; of this 

 question, however, we will have something to say further on. 



Of these birds, whose osteology we will now examine, by far the 

 largest number of them are associated in the genus Falco, and a 

 good idea of their principal characters may be obtained by a study 

 of the skeleton of such a fine representative of them as our Prairie 

 falcon (Falco mexicanus), of which I have a good series. 



In the skull of this species we find the superior osseous mandible 

 rather short, thick, stout, broadly rounded from side to side 

 superiorly over the base, powerful, hooked at the apex; and show- 

 ing a secondary hook, one upon either side on the tomial edge, just 

 above the apical hook. The narial apertures are distinct, sub- 

 circular, with their sharp edges slightly raised without. The sep- 

 tum narium is completed fully in bone, but is somewhat hidden 

 from an outside view, through the nostril, by a small osseous scroll 

 that stands just within that aperture. It is fused with the mesial 

 surface of the adjacent nasal, and somewhat attached to the septum. 

 It has the character of a turbinal. Each nasal is pierced by a single 

 small foramen, and a similar one pierces either lacrymal, close to 

 its anterior border, at the junction of the horizontal and descending 

 portions. This foramen is often seen in the edge of the bone in 

 Buteo, the eagles and others. Falco mexicanus has a very 

 large lacrymal, and, as in all true falcons, it has a very prominent 

 superior limb that curves far backward, and is without an " accessory 

 piece " at its extremity. Between it and the descending portion there 

 is a slight constriction, while the descending portion itself is of a 

 quadrilateral outline, anteropo>steriorly compressed, being fused by 

 its mesial margin with the pars plana, as is the bone above (in adult 

 individuals) fused with the frontal and nasal. These several 

 sutures are obliterated in very old birds of this species. 



