WILLISTON: RESTORATION OF ORNITHOSTOMA (PTERANODON). 49 
Femur. 
The head of the femur is nearly 
hemispherical, supported upon a 
cylindrical neck, placed at only 
a slight angle with the long axis of 
\the bone. The trochanter is low 
and obtuse, situated at the top 
ge) hae of the long axis of the shaft. The 
x Oe Thea 
shaft is of nearly equal width 
throughout, with a strong anterior 
curvature. From alittle below the trochanter, the 
outer border of the shaft is markedly concave, the 
inner correspondingly convex. The distal articu- 
lation is broad, with two, shallow, trochlear 
grooves, separated by a median convexity or ridge. 
It permits only a moderate amount of flexion with 
the tibia, less than 45° from a straight line. In 
the popliteal depression there is a small pneumatic 
opening. 
Tibia. 
The tibia is a slender bone, gradually decreasing 
in width from the proximal end to near the distal 
articulation; the front border is straight, the pos- 
teriur gently concave. The proximal articular 
surface is at right angles to the long axis of the 
bone, and is broadest transversly on the posterior 
part. On the outer surface, about fifty mm. below 
the end of the bone, is a roughened tubercle about 
one half inch in length, for muscular attachment. 
The distal extremity, representing, I suppose, the 
co-ossified proximal row of the tarsus, forms a 
pulley-like mass, the articulation extending through 
nearly three-fourths of a circle, moderately deeply 
grooved in the middle. On the inner side, just 
above the articular border anteriorly, there is a 
well-marked tubercle for ligamentous or muscular 
attachment. 
Tarsus. 
There are but two tarsal bones, irregular in shape 
and flattened. They lie side by side, and are not 
at all superimposed. Their greatest and least 
IV diameters are respectively, 20 and 6, and 20'and 7 
Leg of Ornithostoma tye ; 
ingens, one-fifth na- millimeters, 
tural size. 
