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ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



three toes, the third to the fifth of the normal mammalian foot. Only 

 one of these, the inner or digit III, possessed a claw. Of the lost toes 

 only a mesocuneif orm, one of the inner ankle or tarsal bones, remains. 

 Differences from Megatherium would appear to lie possibly in the 

 shape of certain of the tarsal elements; the astragalus, for example, 

 the tarsal bone that articulates with the tibia, has a better developed 

 knoblike portion for the inner part of the "ankle joint." 



Figure 6. — Right hindfoot of Megatherium americanum Blumenbach (after Richard Owen) 

 from Argentina. The knoblike process (top of foot) on astragalus is rather different than 

 in the Eremotherium foot. Outer view as in figure 5. About 1/8 natural size. 



Figure 7. — Right (figure on left) and left sides of an anterior dorsal vertebra of Eremo- 

 therium, showing a remarkable lack of symmetry or difference in development. On the 

 right side of the vertebra (figure on left) the pedicle or support for the arch and spine is 

 strikingly slender, and the upper surface of the centrum below is much more deeply 

 excavated. About 1/6 natural size. 



An additional feature, comment on which has not been noted else- 

 where for this animal, relates to the lack of symmetry observed in 

 dorsal vertebrae from the third or fourth to about the sixth. In these, 

 the right neuropophysis or pedicle of the neural arch is much more 

 slender than the left (fig. 7) so that there is a much greater opening on 

 the right side between the arches of adjacent vertebrae. Also the top 

 surface of the centrum is noticeably excavated on the right, as though 

 the thoracic nerve on this side were much larger than on the left, or 

 than normal, as it separated from the spinal nerve and passed out be- 

 tween the adjacent vertebral arches. 



