278 
PATAGONIAN EXPEDITIONS PALAEONTOLOGY. 
cnemial crest, which, after a short course, suddenly narrows and is con- 
tinued as a mere linea aspera for nearly two-thirds of the length of the 
bone. The shaft rapidly narrows and becomes very much compressed 
laterally ; the middle portion is stout, trihedral in section, with concave 
posterior face, owing to the elevation of the lateral borders. Distally, it 
widens very much, attaining nearly the width of the proximal end, but is 
also greatly compressed antero-posteriorly. The internal border of the 
shaft, except just below the head, is nearly straight, while the external 
border is deeply concave, making a very wide interosseous space. At the 
distal end the inner border is thick and rounded and terminates in a short, 
but very heavy internal malleolus, on the inner side of which is a massive 
and rugose prominence ; the outer border, on the other hand, is a thin 
edge. The astragalar surface is broad transversely, narrow antero-pos- 
teriorly, especially the external portion ; it is very obscurely divided into 
a larger and moderately concave surface for the inner condyle of the 
astragalus, which is produced and slightly reflected upward upon the 
posterior side of the tibia, and a much narrower and nearly flat surface 
for the external condyle. On the anterior side there is no intercondylar 
tongue, but a low and inconspicuous one appears on the posterior side. 
Connected with this external astragalar surface and demarcated by slight 
difference of level, is the small, D-shaped fibular facet, which presents 
distally, the tibia here resting directly upon the fibula. 
Of the fibula only the distal portion is known. The shaft is very 
heavy, bowed outward and of subcylindrical shape, while the distal end 
is very massive both in breadth and antero-posterior thickness. A short, 
but prominent interosseous crest arises near the bottom of the shaft. 
Internally, the fibula extends beneath the tibia, which rests upon it and 
the surface for which faces almost directly upward. On the external side, 
near the anterior border, is a large and prominent rugosity, which corre- 
sponds to that on the postero-internal angle of the tibia. The astragalar 
facet is large, slightly concave in both directions and has a moderate 
inclination outward and downward. The facet for the calcaneum is very 
large, slightly concave and very oblique, presenting backward almost as 
much as distally. 
In this most peculiar animal no structure is more remarkable than the 
pes, the manner of using which is highly problematical. The astragalus 
(PI. XXX, fig. 4), though fundamentally similar to that of the other 
