30 
PATAGONIAN EXPEDITIONS ! PALEONTOLOGY. 
The straight femoral shaft is slightly flattened transversely (Pis. IV, 
figs. 1-3 ; VI, fig. 4). The head is large and hemispherical, with a deep 
pit for the round ligament (not shown in the figures). The major tro- 
chanter slightly exceeds the head in elevation, from which it is separated 
by a shorter notch than in Hegetotherinm. The trochanter minor is very 
large and sharply pointed. A prominent third trochanter is present, situ- 
ated on the opposite side of the shaft and slightly farther down than the 
trochanter minor. The condyles are large, the inner exceeding the outer 
A in width and posterior extension. Both are slightly convex transversely. 
The patella (PI. IV, figs. 8, 9) is quite narrow, tapering distally. An- 
teriorly, it is strongly convex in all directions and rugose for tendinous 
attachment. Posteriorly, it is divided by a median keel into two equal 
concave articular surfaces, occupying the entire posterior aspect of the 
bone except at the extreme distal end. 
The tibia and fibula (Pis. IV, figs. 4, 5; VI, fig. 5) are usually unfused 
both proximally and distally, but in some specimens partial fusion has 
taken place distally. The tibial shaft is slightly arched inward and the 
fibular shaft outward, inclosing a large lens-shaped interosseous fossa. Of 
the condylar surfaces, the outer is the larger and more nearly circular. 
The spine is comparatively inconspicuous. The proximal fibular facet 
presents outward and downward, and is completely overhung by the outer 
condyle. It is a dumb-bell-shaped surface, sigmoid in antero-posterior 
section and plane transversely. The tibial shaft is triangular in cross- 
section proximally, becoming circular in cross-section toward the middle 
portion of the shaft. Externally, it is deeply excavated longitudinally, 
while the internal surface is quite smooth and slightly convex transversely. 
The cnemial crest is prominent, terminating in P. australe in a rugose 
tubercle. Distally, the tibial shaft is slightly expanded transversely, sup- 
porting externally a large rugose surface for ligamentous union with the 
fibula. The distal articular surface (PI. IV, fig. 5), which is placed some- 
what obliquely with respect to the median plane of the shaft, is divided 
by a prominent keel into two approximately equal grooves for the crests 
of the astragalar trochlea. The internal malleolus is quite long, support- 
ing a plane surface for lateral articulation with the internal astragalar 
crest. 
The fibula (Pis. IV, fig. 18; VI, fig. 5) is quite slender, slightly arched 
externally and greatly compressed laterally, with strongly marked interos- 
