492 LAND MAMMALS IN THE WESTERN HEMISPHERE 



firmly coossified, formed a very long compound bone, which 

 was broad transversely and thin antero-posteriorly. The long 

 femur had only a small and inconspicuous third trochanter 

 and the shaft was broad and thin, being flattened, or "com- 

 pressed" antero-posteriorly. The tibia and fibula were united 

 at both ends ; the former was very heavy at the upper end, but 

 diminished downward in width and thickness, and the fibula 

 articulated with the calcaneum, as in the artiodactyls. The 

 feet were tridactyl and had mesaxonic symmetry ; that is to 

 say, the median digit, or third of the original five, was sym- 

 metrical in itself and was bisected by the middle hue of the foot, 

 while the lateral toes (second and fourth), each of which was 

 asymmetrical, formed a symmetrical pair. It is this perisso- 

 dactyl character of the foot to which Darwin refers when he 

 says that \Macrauchenia "belongs to the same division of 

 the Pachydermata with the rhinoceros, tapir and palseothe- 

 rium." On the other hand, the very significant structure of the 

 ankle-joint was radically different from that of the Perisso- 

 dactyla; not only did the calcaneum have a special facet for 

 articulation with the fibula, but the lower end of the astragalus 

 was a convex "head," resting only on the navicular, as in the 

 tToxodontia, fCondylarthra, Hyracoidea and other very 

 primitive groups of hoofed animals and in clawed mammals 

 generally. Such a combination of characters is not known in 

 any of the perissodactyls and precludes the reference of the 

 fLitopterna to that order, though such a reference is strongly 

 maintained by several authorities. The ungual phalanges 

 were small and appear to suggest the presence of pads on the 

 feet. 



The appearance of ^Macrauchenia in life must have been 

 sufficiently strange. The small head with its proboscis and the 

 long neck and legs should probably be regarded as indicative 

 of browsing habits, though the hypsodont teeth show that 

 grazing was at least an occasional mode of feeding. The long 

 limbs and short feet gave to the extremities an appearance un- 



