28 PATAGONIAN EXPEDITIONS: PALEONTOLOGY. 



second trochanter is a compressed conical tuberosity, prolonged distally 

 into a ridge ; the third trochanter is prominent, though rather small, and 

 has a more distal position than in Eqims : the shaft is long, quite slender 

 and laterally compressed. All of the femora certainly referable to the 

 present genus, which I have seen, are so injured that the pit for the 

 plantaris muscle is not shown, but as this fossa appears in all the other 

 genera of the family, it was doubtless present in Diadiaphorus also. The 

 trochlea is asymmetrical, with the inner border decidedly more promi- 

 nent than the outer, and the suprapatellar fossa is deep : the condyles are 

 quite small, projecting but little behind the plane of the shaft, and are 

 asymmetrical, the external one being larger and more convex than the 

 internal : there are no distinct tuberosities. 



The patella is strikingly different from that of Theosodon, being short 

 proximo-distally, broad, very thick, and rugose on the anterior surface, 

 while the articular facet for the femoral trochlea is quite small. 



As in all of the Santa Cruz representatives of the Litopterna, the leg- 

 bones (PI. Ill, fig. 7) are separate. The tibia is quite stout and somewhat 

 shorter than the femur ; the condyles are widely separated, making a bifid 

 spine : the cnemial crest is prominent and very heavy proximally, but 

 extends only a short distance down the shaft and terminates abruptly, and 

 the sulcus for the tendon of the extensor longus digitormn is much shal- 

 lower than in Eq^ms. The shaft is stout, almost straight and of subtri- 

 hedral section, becoming transversely oval near the distal end, which is 

 somewhat broadened and thickened : the astragalar surface is divided into 

 two unequal facets, of which the internal is the larger, by an intercondylar 

 ridge, which projects as a prominent tongue on both dorsal and plantar 

 sides, and is especially heavy on the latter ; the dorsal tongue bears an 

 articular surface for the pit on the neck of the astragalus ; the internal 

 malleolus is much reduced. 



The fibula is far more reduced than the ulna : the shaft is straight, slender, 

 laterally compressed and of irregularly trihedral shape ; near the distal end 

 it becomes quite thick antero-posteriorly, but remains narrow transversely : 

 on the external side of the distal end is a very deep sulcus for the peroneal 

 tendon, the borders of which groove are thickened and form tubercles 

 distally. The distal facet for the tibia is small and confluent with the 

 large plane surface for the astragalus ; the calcaneal facet is relatively large 

 and quite complex, being composed of an anterior convexity and a pos- 

 terior concavity. 



