NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 69 



Meniscotherium, and that the internal malleolus is obliquely truncate 

 and acuminate as in many creodonts. In Phenacodus the internal 

 malleolus is much more blunt. It may be further noted that the 

 tibia in Phenacodus is essentially straight, not bowed as in Menisco- 

 therium, and the shaft is much more robust. 



A distal portion of a tibia is known for Hyopsodus paulus, as 

 well as for H. zvalcottianus. Both show the anteroposteriorly concave 

 surface for the astragalus which lacks any clearly defined median 

 flexure, denoting a very shallow trochlear groove in the latter. This 

 surface, moreover, is not so oblique transversely as in Menisco- 

 therium. The internal malleolus is abruptly truncated distally and 

 the rounded anteromedial margin becomes more anterior in position 

 proximally on the shaft, in the direction of the cnemial crest. A 

 lateral crest for the interosseous membrane is somewhat better defined 

 in the H. paulus specimen, but at its distal extremity, at the margin of 

 the astragalar facet, the internal malleolus is roughly acuminate and 

 I find no evidence of a facet for the fibula. 



FIBULA 



The Meniscotherium fibula is a decidedly slender bone with moder- 

 ately enlarged extremities (see pi. 9). The shaft is slightly thicker 

 distally and this portion shows a better defined anteromedial crest 

 for the interosseous membrane. The proximal extremity exhibits a 

 proximally facing, anteroposteriorly elongate oval concavity for artic- 

 ulation with the external tuberosity of the tibia. The anteropos- 

 teriorly expanded proximal extremity affords attachment for muscles 

 believed to be the peroneous longus and the soleus, and more medially 

 the tibialis posterior, that aid in flexing and extending the foot. The 

 distal extremity exhibits an oblique, distomedially facing surface 

 which articulates with the outer side of the astragalus and with the 

 calcaneum. On the lateral surface of the extremity is a short but 

 prominent longitudinal crest or process bounding anteriorly a smooth, 

 broad groove, evidently for the tendons of the peroneus muscles. 



The Phenacodus fibula has a similar appearing proximal extremity, 

 but the shaft is sturdier and the distal extremity more enlarged. It 

 also appears that the fibula in Phenacodus makes a more expansive 

 contact with the tibia, both proximally and distally. Moreover, the 

 lateral crest or process on the distal extremity is much less developed 

 than in Meniscotherium. 



The distal portion of a fibula belonging to Hyopsodus paulus 

 shows a somewhat enlarged external malleolus with an oblique facet 



