34 Osteology of Circus hudsontus. 
compared with similar ones made upon the skeletons of allied 
forms. So this will be deferred for another occasion. 
I complete this paper with a recapitulation of the principal char- 
acters of the skeleton in this Hawk. 
OSTEOLOGICAL CHARACTERS OF CIRCUS HUDSONIUS. 
1. The nasal septum in the dried skull is not complete, there 
being a deficiency at its superior posterior angle. 
2. The osseous nares are of an elliptical outline on either side, 
the major axis being in the same straight line with the imaginary 
one drawn between the anterior point of the fronto-lacrymal articu- 
lation and a point five millimetres above the apex of the superior 
mandible. 
3. The maxillo-palatines are spongy bones, being attached to 
the nasals and nasal septum in the rhinal chamber, merging into 
each other anteriorly only, being produced posteriorly, parallel 
and separate, as far as an imaginary line joining the antero-inferior 
angles of the ethmoidal wings. 
4. A circular foramen exists on either side, immediately beyond 
the maxillo-palatine plate of the maxillary. 
5. The vomer is a narrow plate of bone, curving upwards, then 
forwards, to terminate in a free-pointed extremity. More than its 
half lies between the maxillo-palatines. Behind, it is anchylosed 
with the palatines. 
6. The interorbital septum has an elliptical fenestra in it of 
some size. 
7. The canal for the passage of the olfactory nerve is double. 
8. The larcrymals are freely articulated in the adult; and have 
no additional pieces at their outer extremities. 
The basi-sphenoidal processes are present but rudimentary, not 
reaching the pterygoids. 
10. The outer posterior angles of the palatines are rounded, and 
for the most part these bones lie in the horizontal plane. 
11. The mandible is without a ramal vacuity. (Negative 
character. ) 
12. The axial skeleton contains forty (40) vertebrae; the first 
pair of free ribs are attached to the thirteenth ; the dorsal vertebree 
are freely movable upon one another ; the twentieth vertebra is the 
first one that anchyloses with the pelvis; the thirty-sixth is the 
