Osteology of Circus hudsonius. 52 
face is powerfully grooved for the passage of the flexor tendons, 
and its proximal end is fashioned to articulate with the tarso-meta- 
tarsial trochleee. 
The articular surface intended for the proximal end of the 
phalanx beyond, occupies a space both above and below the end 
of the bone. It is surrounded by a raised marginal rim, which 
allows the succeeding phalanx scarcely any motion in the vertical 
plane, and these latter joints of the digits have it in no other. 
The second phalanx of the inside digit very much resembles the 
first digit of hallux ; it is, however, a smaller bone, the same may 
be said of its claw, though we note that the curvature is less in 
the one under consideration. 
The irregular first phalanx measures seven millimetres in longi- 
tudinal axis between parallel lines which touch its most distal 
and proximal points. Second phalanx measures 1.7 centimeters 
and the chord of the claw measured as in the first instance 1.9 
centimeters. 
The four phalanges of the middle digit in Cz7cus all more or less 
resemble the typical style of the joint, 7. ¢., like first phalanx of 
hallux. From proximal to distal one, the first three measured 
1.6, 0.8, and 1.5 centimeters respectively ; the chord of the claw 
being 1.6 centimeters. 
Measured in the same manner the joints of the outside toe give 
0.8, 0.5, and 0.45 centimeters, and the chord of this claw 1.3 cen- 
timeters. 
In some respects these proportions of the phalanges agree with 
similar measurements made upon certain species of Owls, and in 
others with the Falcons, but this subject I propose to hold in 
reserve for another memoir, in which it will be fully treated, and 
properly illustrated. 
Ossification occasionally extends, in C7zrcus, to some of the 
tendons of the lower extremities, in subjects several years old. 
Among the Owls this condition is the rule. I have seen it in 
Bubo, Strix, Asto, Surnia and Speotyto. 
The usual parts of the sense capsules also ossify, as the sclerotals 
of the eye, and the columella auris of the organ of hearing. 
It was the writer’s intention to present a table giving measure- 
ments in centimeters and fractions, of the various parts of the 
skeleton of Crvcus ; but upon second thought this idea was aban- 
doned, as such measurements are of far more use and interest when 
