14 Osteology of Circus hudsonius. 
tance. In the parapophyses the form of the diminitive rib begins 
to be suggested, accompanied by a corresponding enlargement of 
the vertebral canals. On the centrum, the articular facets are 
larger, and the anterior one, especially, deeper. The neural 
canal, still circular, is here larger than we found it in the axis. 
It seems to have the least calibre in the sixth vertebra. 
In figure 7, the anterior vertebra shown,*is the ¢hzrteenth, and 
it departs very markedly from the last one described. Its neural 
spine now becomes a high quadrate crest nearly as Jong as the 
centrum of the bone. 
The transverse processes are heavier, and the bases to the 
zy gapophyses very substantial, with little change in the direction 
of the facets. A rudimentary free rib has made its appearance, 
the body of which is no longer than its neck. I should have 
noted a pneumatic foramen on the lateral aspect of the centrum of 
the twefth vertebra ; it is still larger here ; is seen in the four- 
teenth ; largest of all in the fifteenth; very minute in the suc- 
ceeding one ; and disappears in the seventeenth. 
The calibre of the neural canal in the thirteenth vertebra is 
circular and large—it gradually diminishes to the nineteenth, 
where it is just a little more than half the size. 
The centrum of the thirteenth vertebra is broader than it is deep, 
and this segment is quite short from before, backward. Below, a 
tricornute hypapophysis is beginning to be developed. In the 
fourteenth vertabra the neural crest is a little longer but no higher ; 
the transverse processes are still more spreading, while the free 
pair of ribs are now quite long, though they do not reach the 
sternum, or rather are not met by costal ribs. ‘They are devoid 
of epiplural appendages. ‘ The centrum is evidently becoming 
narrower and longer, and this contraction and lengthening grad- 
ually continues through the nineteenth or last free vertebra we 
find before reaching the pelvis, in which the centrum is twice as 
long as itis wide. The articular facets also increase proportion- 
ately in size; the periphery of the posterior articular facets on 
the centrum of the nineteenth vertebra is fully double the circu- 
larity of its neural canal, the measurement for the latter being 
taken over the middle of the centrum. 
Returning to the fourteenth vertebra, we find the tricornute 
hypapophysis but little larger than we found it in the thirteenth, 
but an evident disposition to contract at its base and project into 
