Osteology of Circus hudsonius. 29 
bone is held.vertically against a plane surface tangent to these 
points, the axis of the shaft is very nearly perpendicular to the 
plane. This is by no means the rule with a great majority of 
birds, where the inner condyle is produced beyond the outer one. 
It is well shown in a specimen of the femur of Geococcyx before 
me. 
The inter-condyloid fossa is broad and fairly divided from the 
popliteral depression by a low transverse bar. As usual, the outer 
condyle is vertically cleft behind to afford an articular cavity for 
the head of the fibula. The little tuberosit’es for muscular and 
ligamentous insertion about this end of the femur in (77cus are 
well marked, and the foramen for the entrance of the medullary 
artery occupies its usual site on the posterior aspect of the shaft 
below the juncture of the upper and middle thirds. 
In the skeleton of C77cus, as it is ordinarily prepared for study, 
the @/dza and fbuda are highly characteristic of the non-pneumatic 
class of bones, being dark, ayd for the most part of a deep amber 
color and greasy. The former is but little curved forward, as we 
sometimes see it, the shaft being very straight from any point of 
view (Figs. 12 and 14). Seen directly from above, the proximal 
articular surface for the condyles of the femur is nearly square 
(Fig. 14). The intercondylar convexity is but feebly pronounced, 
and the rotular crest of the bone rises but slightly above the gen- 
eral undulating articular surface. The apex of the entocnemial 
ridge points directly outwards, the opposite or procnemial rldge 
being developed as a crest parallel with the outer surface of the 
fibula, and produced some distance. down the shaft of the bone. 
Below, and on the outer side of the shaft of the tibia, we find a 
long, well developed, fibular ridge, for the usual articulation of 
that bone. Further down the shaft its continuity is subeylindrical 
on section, at least as far as where it begins to become antero- 
posteriorly flattened above the condy!es. 
The usual oblique bony bridge for the retention of tendons is 
seen on the anterior aspect just above the condyles, and above it 
again the two tubercles, one on either side, for the attachment of 
the ligament that performs a similar function. Of these latter 
the inner is the higher on the shaft. The tibial condyles are 
nearly of a size, the outer one being produced the further up the 
shaft posteriorly. In this situation the articular surface merges 
across the inter-condyloid space. On the outer aspect of the inner 
