12 Osteology of Circus hudsonius. 
quite broad. Below, two short processes are directed backwards: 
behind the part bearing the articular cup. 
The ‘‘odontoid process’’ of the a1zs is compressed from above 
downwards, its surface being flat superiorly, convex below. ‘The 
neural canal is circular, and the arch above supports three stumpy 
processes, the lateral diapophyses and the neural spine. Beneath 
the odontoid process the atlantal articular surface is a shallow con- 
cave ellipse, placed transversely. Behind this the body of the 
bone is compressed from side to side, with longitudinal median 
crest, terminating posteriorly in a knot-like process. 
The third vetebra presents pre- and postzygapophyses ; the ar- 
ticular facets on the first being directed upwards, those behind 
directly downwards. These processes in this vertebra are united _ 
by a horizontal plate of bone, which lends to this segment a very 
solid appearance not possessed by those behind it. It is pierced 
about the middle on either side, near the outer margin, by a minute 
foramen. A median neural spine projects backwards from the pos- 
terior border. 
The neural canal is cylindrical, and the arch slightly overhangs 
it behind, but recedes from its anteriorly. On either side the ver- 
tebral canal is present a minute perforation; the parapophyses 
having short spiculz directed’ backwards. A median, oblong 
hypapophysis is situated posteriorly directly above which is the 
articular facet for the fourth vertebra. It is concave from above 
downwards, and convex from side to side, the reverse being the 
case in the anterior facet, which is directed downwards and 
slightly forwards. 
In the fourth vertebra the pre- and postzygapophyses are con- 
nected by a delicate spine on either side, the articular surfaces on 
the former are slightly inclined towards the median plane and 
each other, the reverse being the case on the latter. The neural 
spine is more stumpy and has worked towards the middle of the 
arch ; the canal is smaller and still circular; while the vertebral 
canals are larger, longer, and their lateral wall is perforated on 
on either side by a small foramen. The parapophysial spines ex- 
tend backward as far as the posterior articular facet, and the hypa- 
pophysis is in the middle of the body of the vertebra. 
In the //th vertebra the neural spine still maintains its position 
as in the last segment, but is rapidly disappearing. The facing 
of the articular surfaces on the zygapophysial processes is more: 
