618 GEOLOGICAL SURVEY OF THE TERRITORIES. 
enemial ridge, though it is no more prominent there than at any other 
point, but in many birds it is so produced as to form a process of 
some size, to which these terms are applied. Externally and poste- 
riorly the margin is roughened for the attachment of ligaments that 
bind the head of the diminutive fibula to this bone. In the middle of 
this articular surface is to be seen a tuberosity, on either side of which 
are the depressions for the femoral condyles. Produced downwards, 
anteriorly from the rotular ridge are the cnemial ridges; these have their 
crests bent slightly outwards, and they merge into the shaft below, 
abreast the superior point of the fibular ridge. Of the two, the outer 
or ecto-cnemial is the shorter; that is, it does not extend so far down 
the shaft as the inner or pro-cnemial. They have between them an 
ovate concavity, with the larger end above, the lower end subsiding 
upon the shaft with the ridges themselves. The vertical elevation on 
the external aspect of the shaft for articulation with the fibula runs 
down the side but a short distance; alittle below its abrupt termination 
may be observed in a line with it, the nutrient foramen, entering very 
obliquely from above downwards. After leaving the fibular ridge as far 
as the point where the bone begins to expand transversely at the distal 
extremity, the shaft is remarkably smooth and nearly cylindrical. This 
transverse and distal expansion is checked, both anteriorly and pos- 
teriorly, by abruptly meeting the distal condyles, the point of meeting 
perhaps being rather the higher behind. The condyles, differing but 
little in size, are singularly uniform as to shape, with their curved sur- 
faces downwards, being flat on their outer aspects, with a raised rim 
bounding them in each case. They stand out prominent and apart. 
Anteriorly their convex surfaces are the widest, behind they slightly 
approach each other, and the articular convex surface is narrowest on 
the outer condyle. The intercondyloid notch is deep, and appears 
equally well marked throughout its extent. Immediately above it, ante- 
riorly, there is a deep triangular depression; another, and more shallow 
one, is found behind in the corresponding locality. Up the shaft a short 
distance on the inner side, anteriorly, is a little tubercle, to which is at- 
tached the ligament that binds down some of the strong tendons of the 
extensors. This ligament crosses the anterior triangular depression 
mentioned above, obliquely, to be inserted near the external condyle 
superiorly. This is the arrangement also in Bubo virginianus, but in 
some of the Hawks this ligamentous bridge has become thoroughly ossi- 
fied, forming a strong bony band across the concavity in question. It 
is interesting to remark here, however general the rule may be as ap- 
plying to the diurnal and nocturnal Raptores, that whereas this band is 
ligamentous in the tibia in some of the Owls, a bony one fulfilling the 
same function is found in them just below the head of the tarso meta- 
tarsus; these conditions are just reversed among some of the Hawks. 
In fact, we Know of no exception to the arrangement just mentioned for 
the Owls; even Surnia funerea has this bony bridge on the tarso-meta- 
tarsus very prominent, and on the inner side of the upper third it bemg 
much in the same position as we find it in the well-known exception to 
the Hawks, that is, in Pandion. In short, among the Raptores it seems 
to be found among those birds that possess the reversible toe. Usu- 
ally, in old birds of this species, the jibula is firmly anchylosed to the 
entire length of the fibular ridge of the tibia; arching outwards, its head, 
surmounted by an antero-posteriorly elongated facet, rises a little above 
that bone at the point where it is attached to it by ligament. This is 
the larger part of the shaft in regard to size. Below the ridge this bone 
becomes simply a delicate little spine, that emerges into the shaft of the 
