NO. 2 A STUDY OF MENISCOTHERIUM — GAZIN 59 



the second metacarpal is transversely convex but slightly concave 

 dorsoventrally. It articulates medially by a narrow but dorsoven- 

 trally elongate facet with the trapezium but slightly, if at all, with the 

 magnum along its rather thinner lateral margin. It is excluded from 

 contact with the lunar by articulation between the scaphoid and 

 magnum. 



The Phcnacodus trapezoid is not nearly so compressed and pre- 

 sents a quadrilateral rather than nearly triangular dorsal surface. 

 The distal surface for the second metacarpal is similar to that in 

 M eniscotherium , but the proximal surface for the scaphoid is more 

 nearly flat. The medial surface exhibits facets for the trapezium, 

 and the lateral surface, unlike M eniscotherium, shows a broad cres- 

 centic facet for the magnum. There may have been also limited 

 contact with the lunar proximodorsally on the lateral surface, 

 although Cope thought not. 



Magnum. — The M eniscotherium magnum is an irregularly shaped 

 bone relatively narrow transversely and with a proximodistally 

 restricted dorsal exposure. It has a nearly triangular shape in lateral 

 or medial view with the deeper median portion surmounted by a 

 knoblike proximal convexity which with the proximodorsal slope of 

 this triangle articulates with the lunar. Adjacent and parallel to this 

 lunar facet but on the medial surface, the magnum shows a facet for 

 the scaphoid (no central). Along the ventral margin of the medial 

 surface there is an arcuate, slightly concave and elongate surface 

 for the base of the second metacarpal. This surface makes a nearly 

 right angle with the dorsoventrally concave distal surface for the third 

 metacarpal. The entire proximodistal extent of a little more than the 

 dorsal half of the lateral surface articulates with unciform. The ven- 

 tral part of the magnum is slightly enlarged and extended somewhat 

 beyond the trapezoid and unciform, presumably supporting attach- 

 ment of a part of the flexor brevis pollicis and possibly certain 

 adductor muscles. 



The dorsal surface of the Phcnacodus magnum is much deeper 

 proximodistally so that the bone does not appear so nearly triangular 

 in lateral or medial view. Also, the surface for the lunar, imme- 

 diately dorsal to the proximal hump or knob, is more concave. Artic- 

 ulations for the second and third metacarpal and for the unciform 

 are similar to those in M eniscotherium, but there may be no artic- 

 ulation with the scaphoid, or it is restricted to a small area on the 

 medial side of the proximal apex. On the other hand, articulation 

 with the trapezoid is rather extensive in the dorsal part of the medial 



