Osteology of Circus hudsonius. 19 
angle is rounded, the anterior border of the keel being concave, 
while the inferior one presents a graceful convex curve. Poste- 
riorly it terminates at the apex of a triangular smooth surface, 
the outer basal angles of which are opposite the foramina in the 
xiphoidal extremity (Fig. 8). The line of union between keel 
and body is rounded, being concave outwards. 
Marked differences occur in the manubrium of Hawks; here in 
C7rcus it is a stumpy process, generally inclined upwards, having 
a sharp median edge below and a triangular anterior surface. 
Among the falcons (Falco richardsoniz), it is a narrow spicula of 
bone, directed forwards and upwards ; but what is most singular, 
there exists in these birds a second process that spring; in the 
median line from the border of the body above. These two pro- 
cesses have the coracoidal grooves between them. 
The grooves for the coracoids decussate in Czrcus, their inner 
ends terminating in points—they decussate still more in /a/co, 
where their inner énds are rounded. Such a dezussation of the 
coracoidal beds in likewise to be se2n in the Herons, as in the 
genus Ardea. 
In the specimens of all the /a/conide before me, it is the right 
coracoidal groove that is the anterior one, and overlaps the supe- 
rior surface of the base of the manubrium. As well as I can 
remember such is also the case with the Herons. 
Returning now to the spinal column, we find that the ¢twezteth 
vertebra of Circus becomes anchylosed beneath theilia. Its broad 
neural spine has fused into one piece in common with the others 
that extend back as far as the sacrum; its diapophyses are half 
covered by the anterior iliac borders, and these with the next ver- 
tebra behind show the facets for the two pair of ribs already 
described above, which are here over-arched by the ilia (Fig. 7). 
The anterior aspect of the twentieth vertebra presents all the 
requirements for articulation with the one next beyond, in its 
prezygapophyses, and in its centrum. Metapophysial spines 
however, are only thrown back by the segment before it, while 
the locking of the neural spines does not take place. 
This description of the twentieth vertebra brings us to a point 
where we must needs take into consideration the feluzs of Czrcus. 
(Figs. 7 and 10). Upon superior view of this bone (Fig. 10) we 
observe that the neural spine or rather its upper surface, projects 
forwards as a broad process between the ilia, and is roundly 
