Art. X.—OSTEOLOGY OF CIRCUS HUDSONIUS. 
By RoW. SHupEED Ty VED... “Mee 
The object of the present memoir is simply to present a detailed 
account of the osteology of a good representative American 
Hawk. For several years past I have been collecting material 
with the view of monographing the subject of .the osteology of 
North American Falcones, but at the present time this mterial 
is not quite sufficiently extensive to undertake the work in the 
way I have hoped to complete it. Several years ago I published 
monographs devoted to detailed descriptions of the skeletons of 
Speotyto cunicularia hypog@a, and the Family Cathartid@, so the 
principal part still left undone in this field, for our birds of prey, 
is among the Hawks, Eagles, Kites, the Osprey, Falcons, and 
some of the Owls. 
Of the Skull,—In dealing with this part, as well as the remain- 
der of the skeleton of C7vcus, I will take into consideration only 
the skull of the adult individual; making no attempt to give 
exact definitions of the boundaries of the several elements of the 
skull, a thing which is only possible in immature specimens. 
We observe upon lateral view (Fig. 1) of the skull of this 
Hawk that the premaxillary is produced downwards anteriorly 
into a sharp-pointed hook. The upper boundary of this, strongly 
convex, forms a little less than half of the culmen, commencing 
as it does at the apex of the osseous beak, and extending back to 
where the nasal processes of the bone commence. Here the pre- 
maxillary presents another convexity as it passes over the nostril 
to gradually terminate, where its nasal processes articulate with 
the frontals in the median line. The opposite or posterior margin 
of the hook above mentioned, is likewise convex anteriorly, and 
