22 Osteology of Circus hudsonius. 
The twentieth and twenty-first vertebrae seen beneath the ilia 
have already been sufficiently described. Posterior to them on 
the ventral aspect of the pelvis a considerable swell takes place in 
the column to accomodate the sacral enlargement of the cord. 
This gradually contracts again at a point opposite the anterior 
borders of the acetabule. 
The /wenty-second vertebra throws up both parapophyses and ° 
transverse processes against the ilia. In this the next three suc- 
ceeding vertebrae follow suit. ‘This takes place at the narrowest 
part of the pelvis, and these processes 
are very stout here. 
In the ¢ewernty-s¢xth to the twenty-ninth, 
inclusive the short abutting processes 
cannot. be seen upon direct ventral aspect. 
This is the region of the true “‘ sacrum”’ 
and the foramina of exit for the sacral 
nerves are here double on either side, one 
opening being above another. 
The thirtieth, thirty-first and thirty- 
second vertebre have long parapophyses, 
which amalgamate at their outer extremi- 
ties, where they form a powerful abut- 
ment for the pelvic walls at points oppo- 
site the acetabula. The pelvis of this 
Harrier is deep in all this region, that is, 
posterior to the twenty-fifth vertebra and 
including the three I have just men- 
Ae Dee eee oye 
men as the last. Life size - The pelvic bones behind grasp but two 
more segments of the column, the ¢hzrty- 
third and thirty-fourth vertebrae. ‘These much resemble the ante- 
rior coccygeal ones, especially the last one. 
In the coccyx we find six vertebree freely movable on each other, 
but with nothing peculiar about them. ‘The fourth and fifth of 
this series have equal and at the same time the most far extending 
transverse processes. ‘The width of the last (the sixth) is about 
equal to the first, and the last three ‘have bifid hyapophyses. 
Circus has a very broad and lofty pygostyle, that in the adult bird 
shows but few traces of its original composition. Its anterior edge 
is sharp, while behind it is flattened and narrowly triangular with 
