*J2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 149 



The trochlea for the tibia is shallow but the inner crest, particularly 

 posteriorward, is not nearly so subdued. The inner and outer walls 

 of the astragalus are both somewhat oblique, lacking the striking 

 difference noted in Meniscotherium. On the ventral surface the ectal 

 facet is a short, oval concavity whose long axis is nearly transverse, 

 more oblique to the sustentacular facet than in Meniscotherium. 

 Moreover, it is interesting to note that the groove for the flexor 

 longus hallucis on the posterior margin is surprisingly prominent, 

 better defined than in Meniscotherium, and the astragalar foramen 

 is not centrally located in the groove of the trochlea, but close to 

 the inner crest. 



Calcaneum. — The calcaneum of Meniscotherium is elongate with 

 the posterior (proximal) projection comprising a little more than half 

 the length. The bone is dorsoventrally deep and transversely some- 

 what compressed in the posterior half. It terminates posteriorly in an 

 enlarged, slightly bilobate extremity for the Achilles tendon, extend- 

 ing posteriorly a little more on the medial than on the lateral side. 

 A little forward of the middle of the calcaneum the astragalar condyle, 

 as noted by Cope, is placed diagonally across the superior or dorsal 

 ridge, with its convex articular facet facing anteromedially and 

 slightly dorsally. Anterolaterally the condyle thickens and the 

 rounded dorsal margin articulates with the distal margin of the 

 external malleolus. A prominent ridge on the calcaneum extends 

 anterolaterally to the well-developed peroneal tubercle near the ante- 

 rior (distal) extremity, which bounds dorsally the broad groove for 

 the peroneus longus. The sustentaculum is a prominent knob medial 

 to the astragalar condyle, with a dorsally facing, transversely elon- 

 gate oval facet for the astragalus. This facet turns sharply ventral 

 on the posterior margin of the sustentaculum, as has been noted for 

 the sustentacular facet of the astragalus. The posteroventral sur- 

 face of the sustentaculum is smooth and broadly grooved for con- 

 tinuation of the extensor longus hallucis. The anterior or distal 

 extremity articulates with the cuboid in a dorsoventrally concave 

 and transversely highly oblique facet that extends posteromedially 

 almost to the anterior margin of the sustentaculum. The dorsal mar- 

 gin of this oblique concavity extends dorsomedially from near the 

 peroneal tubercle toward the neck of the astragalus and is less oblique 

 or nearly at right angles to the long direction of the shaft. The more 

 ventral margin extends ventromedially to the inferior margin of the 

 calcaneum. 



The Phcnacodus calcaneum is similar but with stronger, more mas- 



