NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 73 



sive construction. The sustentaculum is deep and thick, not so elon- 

 gate and slender. The lateral crest from the astragalar condyle to 

 the peroneal tubercle is rugged and outstanding, but with less defini- 

 tion of the tubercle itself. The surface for the cuboid extends ventro- 

 medially somewhat oblique, but is much less concave, evidently lack- 

 ing the flexibility of the Meniscotherium articulation. 



The Hyopsodus calcaneum is relatively shorter than that of Menis- 

 cotherium, and the posterior portion between the astragalar condyle 

 and the enlarged tuberosity for the Achilles tendon is a little more 

 compressed transversely. The astragalar condyle is similar but a 

 little less dorsally projecting. The sustentaculum is dorsoventrally 

 more compressed, but anteroposteriorly broader and perhaps a little 

 less extended medially. The shortened anterior portion of the cal- 

 caneum, correlated with the relatively short neck of the astragalus, 

 exhibits a somewhat less oblique and less concave facet for the 

 cuboid, although in its transverse direction it is nearly aligned with 

 the anterior margin of the sustentaculum. The dorsal margin of this 

 surface is transversely shorter and more curved, with a long lateral 

 margin extending down to a more ventrally placed peroneal tubercle. 

 The peroneal groove consequently is decidedly more ventral in 

 position. 



The slender Tetraclaenodon calcaneum has a long anterior or 

 distal portion, in keeping with the elongate neck of the astragalus, 

 as well as a lengthy posterior portion. The sustentaculum is slender 

 and outstanding, about as in Meniscotherium. The articular facet 

 for the cuboid, although oblique and concave, is rather less so than in 

 Meniscotherium, and it does not approach so near the sustentaculum 

 posteromedially. 



Navicular. — The Meniscotherium navicular is proximodistally 

 short and has a deeply concave proximal surface occupied entirely by 

 the head of the astragalus. The rim of the concavity is broadly 

 curved dorsally and medially, but the lateral margin is more nearly 

 straight and rises to a low prominence ventrolaterally. The medial 

 margin, however, rises to a higher, more acute process ventrally, and 

 between these there is a sharp notch in the ventral border for passage 

 of the tendon of the posterior tibialis. The lateral side of the distal 

 surface shows a flat facet for the external cuneiform which is dorso- 

 ventrally elongate and noticeably tapering ventrally. Medial to this 

 the facet for the middle cuneiform is dorsoventrally shorter and dis- 

 tinctly convex. The more ventromedial surface of this convexity 

 articulates with the internal cuneiform, and rises to the prominence 



