Osteology of Circus hudsontus. > Oe 
decided, while those on the posterior pair are borne on projecting 
and diverging limbs of considerable length. ‘The delicate bar 
that connected them on either side, in the fourth vertebra is here 
deficient at the middles. Other features are but slightly modified ; 
the hypapophysis has assumed a position just behind the anterior 
articular surface of the body. 
The neural spine of the sixth vertebra is barely perceptible, and 
the interzygapophysial bar is again intact as a delicate bridge. 
At the base of each postzygapophysis above, a little projection is 
seen, which occurs on the four succeeding segments, both then 
are obliterated. : 
The vertebral canals have the form of a vertical ellipse, and the 
parapophysial spines are again shortening. Beneath, we cbserve 
that the hypapophysis has disappeared, and at its site, in the last 
vertebra, the carotid canal begins to form. ‘The body of this 
vertebra is nearly square on transverse section. But slight modi- 
fication has taken place in the seventh vertebra. ‘The limbs of the 
postzygapophyses are shorter ; the connecting bar is still intact ; 
the neural spine has entirely disappeared ; and the carotid canal 
is deeper and narrower. 
In the ezghth vertebra the interzygapophysial bar is once more 
incomplete, while the changes taking place in the last vertebra are 
becoming better marked. 
Sharp lateral processes form the walls of the narrow carotid 
canal in the zzzth vertebra, and the vertebral canals are nearly cir- 
cular and increasing in calibre. ‘The parapophysial spines are 
nearly as long as the body, while the vertebree are now beginning 
to be shorter and heavier. ‘The anterior pair of articular facets 
look upwards and inwards, the reverse being the case with the 
hinder pair. A tuberous neural spine and hypapophysis make 
their appearance in the /enth vertebra, the latter being in the mid- 
dle of the body. Parapophysial processes are shorter, though 
more pronounced, while the carotid canal has ceased to exist. 
The general form of this vertebra is cubical. 
In the eleventh vertebra the neural spine is more lofty and hooks 
forwards ; the spine beneath forms a low median crest nearly as 
long as the body of the vertebra. The vertebral canals are still 
increasing in calibre. Quite marked changes have gradually 
come about in the ¢wel/th vertebra. ‘The neural spine is very 
pronounced, while the hypapophysis is shrinking again in impor- 
