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ANNUAL REPORT SMITHSONIAN INSTITUTION, 195 6 



Figure 2. — Right forefoot (U.S.N.M. No. 20872, reversed from left, and composite only 

 in part of carpus) of Eremotherium rusconii (Schaub) from El Hatillo. Note absence ot all 

 but a vestige of second, as well as first, digit or toe (on right side of foot). About 1/8 

 natural size. 



Figure 3. — Right forefoot of Megatherium americanum Blumenbach (after Richard Owen) 

 from Argentina. Note presence of complete and well-developed second digit or toe (on 

 right side of foot). Only the first digit is vestigial. Slightly less than 1/8 natural size. 



a better defined digital or trochanteric fossa, or a less deflected greater 

 trochanter as noted by Hoffstetter. 



Probably the most significant difference that distinguishes 

 Eremotherium from Megatherium lies in the structure of the manus 

 or forefoot, not previously noted because of the incompleteness of 

 earlier described materials of Eremotherium. In Megatherium the 

 forefoot has four toes or digits (fig. 3). The second, like the third 

 and fourth, is equipped with a well-developed claw, as shown in Owen's 

 illustrations. Moreover, the first and second phalanges of this toe 

 are separate as in the fourth digit, not co-ossified as in the third. The 

 pollex or "thumb," though, is represented by but a "nubbin" of a bone, 

 a much-reduced first metacarpal. Eremotherium, however, has only 

 three fully developed digits (fig. 2). The wrist bone, known as the 

 trapezoid, normally adjacent to the proximal end of the second meta- 

 carpal, is apparently fused in Eremotherium with both the first and 

 second metacarpals, and the second digit is otherwise represented 

 by only a small vestige of a bone, probably the first phalanx, as indi- 

 cated by a small facet on the distal surface of the fused elements. 



